Method for operating a, in particular gas adaptive, combustion appliance

Abstract

The invention relates to a method for operating a, in particular gas adaptive, combustion appliance, which comprises an oxygen sensor for measuring an oxygen value in a gas to be measured, and a combustion chamber in which an air and fuel mixture is combusted, wherein the method comprises the following steps: initiating a calibration of an oxygen sensor for calibrating the oxygen sensor and initiating a purging of the combustion chamber, wherein the calibration initiation and the purging initiation is set such that the oxygen sensor is calibrated during the purging of the combustion chamber, wherein the oxygen sensor is electrically heated during the calibration.

Description

[0001] Method for operating a, in particular gas adaptive, combustion appliance

[0002] The invention relates to a method for operating a, in particular gas adaptive, combustion appliance. Additionally, the invention relates to a data processing device comprising means for carrying out the method, a computer program product, computer readable data carrier and a data carrier signal. In addition, the invention relates to a combustion appliance with such a data processing device.

[0003] Gas adaptive combustion appliances, in particular gas adaptive boilers are known from the prior art. Such kind of gas adaptive combustion appliances can be adapted to different fuel gas types.

[0004] Gas adaptive combustion appliances were developed to address the broad Wobbe value changes of the fuel supply in Europe and were introduced in 2001. The known gas adaptive combustion appliances are fully premixed appliances equipped with an Adaptive Combustion Control Function (ACCF) that are intended to be connected to gas grids where the quality of the distributed gas is likely to vary to a large extent over the lifetime of the appliance including gas grids for natural gases of the second family where up to 20 mol% H2 is added to the natural gas. Gas adaptive combustion uses at least one sensor signal to adjust the air fuel mixture to maintain a preset value, such as an ionization signal or an 02 signal. The gas adaptive combustion appliance control uses the respective signal and, by controlling the blower and gas valve via for example using a pulse-width modulation (PWM) signal, adjusts the amount of air and gas entering the burner until it the desired value is reached. The gas adaptive combustion allows constant combustion monitoring for optimal efficiency. In addition, there is a scheduled calibration period which occurs based on run time cycles that confirms the system is operating within predetermined specifications.

[0005] Usually, the boiler consists of a fan for modulating the boiler power and a fuel gas valve which controls the air to fuel ratio. The fuel gas valve can be adjusted manually to set the air to fuel ratio at low load. On the fuel gas valve, a motor driven throttle is located which can electronically adjust the flow through a throttle opening downstream of the fuel gas valve opening and adjusts the air to fuelratio. In a gas adaptive combustion appliance, such as a boiler, the gas adaptive combustion appliance controls the throttle position and thus the throttle opening by controlling the throttle motor to get a desired air to fuelratio. It is known for such gas adaptive combustion appliances to comprise an oxygen sensor for determining the gas-air ratio. This ratio is measured with an oxygen sensor in the flue gas. Gas adaptive combustion appliances utilize the relationship between the 02 signal and the air-fuel ratio (also known as lambda A). Gas adaptive combustion appliances have a relationship between 02 and power that can be expressed by an 02 - power curve. At every firing rate, there is a flame ionization value that corresponds to the target lambda (A = 1 .3 in figure below, indicating ~30% excess air). Once defined, the flame ionization curve is used as a target setpoint to control the gas valve. When the 02 signal is lower than expected (high signal indicates low 02, or rich condition), the control decreases gas valve position to return to A = 1.3. Similarly, when 02 signal is higher than expected (indicating excess air too high, or lean condition), the control increases gas valve position to return to A = 1 .3.

[0006] Gas adaptive combustion appliances commonly periodically calibrate to compensate for effects like combustion air temperature / humidity variation, component wear, and fuel composition. Calibration is commonly automatically initiated upon a boiler start several times per month based on an internal counter. When a calibration is required and demand is present, the gas adaptive combustion appliance starts and runs at a constant mid-range firing rate. As an example, the gas valve is opened until lambda equals 1 and a maximum ionization value is reached. This value is then used to shift the ionization setpoint curve. Following this phase, the gas adaptive combustion appliance ramps to low fire and calibrates the minimum opening point of the gas valve. The entire calibration sequence lasts about one minute. In case of using the 02 signal, calibration is done by purging and setting the measured value of 02 related to the 21% 02 of ambient air.

[0007] Ignitions are more reliable with gas-adaptive combustion appliances compared to systems with pneumatic gas I air ratio control where the gas supply rate is pneumatically driven by the air supply rate or vice versa (definition 3.1.201.22 EN 12067-2:2022, 3.117). Gas adaptive ignitions can for example begin with the gas valve opening to a fixed point followed by an automatic ramp up until a flame is detected. This feature assures the system will always light at the proper air-fuel ratio. In contrast, pneumatic gas valves open to the same fixed point at every ignition, which is only changed by a manual adjustment of the gas valve or by changing the fan speed to increase ignition load. This can lead to light-off issues such as noise or ignition failure over time.

[0008] The user requests that the gas adaptive combustion appliance outputs by heat demand. However, it is mandatory to calibrate the oxygen sensor of the gas adaptive combustion appliance to minimize a sensor drift during operation and to guarantee a fail-safe operation of the oxygen sensor and thus of the combustion appliance. The heat output is interrupted during the calibration.

[0009] The objective of the invention is therefore to provide a method by means of which the mandatory requirements of calibrating sensor units is fulfilled and by means of which heat output can be provided essentially uninterrupted by the mandatory sensor calibration when the user demands it.

[0010] The objective is solved by a method for operating a, in particular gas adaptive, combustion appliance, which comprises an oxygen sensor for measuring an oxygen value in a gas to be measured, and a combustion chamber in which an air and fuel mixture is combusted, wherein the method comprises the following steps: initiating a calibration of an oxygen sensor for calibrating the oxygen sensor and initiating a purging of the combustion chamber, wherein the calibration initiation and the purging initiation is set such that the oxygen sensor is calibrated during or after the purging of the combustion chamber.

[0011] According to the invention it is realized that performing the calibration of the oxygen sensor during the purging of the combustion chamber of the combustion chamber has less influence on the heat output of the combustion chamber. Specifically, a heat output usually does not have to be interrupted when a user’s heat demand exists. Thus, it is avoided that the combustion appliances responses slow to a heat demand because it performs a calibration of the oxygen sensor. In other words, the wait time for comfort delivery is reduced, which increases the comfort level of the user of the combustion appliance. Additionally, it is avoided the situation that a mandatory sensor calibration is performed when a heat demand exists. As it is explained below more in detail it is possible to avoid that the calibration is performed at a time when a heat demand exists but by performing the calibration when the combustion chamber is purged it is possible to perform the calibration when the combustion appliance does not output heat.

[0012] According to an aspect of the invention a combustion appliance is provided. The combustion appliance comprises: a fan for controlling an air flow, a fuel valve, in particular a fuel gas valve, for controlling a fuel flow, in particular the fuel gas flow, a burner for combusting an air and fuel mixture, in particular an air and fuel gas mixture, an oxygen sensor for measuring an oxygen value in a gas to be measured and a data processing device for executing the inventive method wherein the data processing device is, in particular communicatively and / or electronically, connected to the fan and fuel valve and oxygen sensor.

[0013] A combustion appliance is a device designed to burn a fuel source in a controlled manner forthe purpose of producing heat. This device typically comprises a combustion chamber where the combustion reaction occurs and means for conveying air and fuel, in particular fuel gas, into this chamber. The air and fuel, in particular fuel gas, can mix before the combustion chamber or inside the combustion chamber. The appliance may also include at least one heat exchanger for transferring the heat generated during combustion to a liquid or air, thereby converting the energy from the combustion process into usable heat. The combustion appliance may be designed to burn various types of fuels, including but not limited to, natural gas, propane, oil, hydrogen, biogas, or solid fuels such as wood or pellets. A combustion appliance can be a boiler, space heater, oven, or a gas water heater.

[0014] In the application a commissioning mode of a combustion appliance is a mode in which the components and / or parameters of the combustion appliance are set so that the combustion appliance can be operated in the operation mode. The commissioning mode can comprise an ignition phase. During the commissioning mode automatic or manual adjustments can be made to components. Specifically, the combustion appliance enables two adjustment possibilities. One possibility is to adjust the throttle unit. This can happen automatically by a throttle element that is adjusted by a throttle motor. Another possibility is to adjust the fuel valve. This can happen manually by manually adjusting an offset element of the fuel valve, namely an offset screw. Specifically, parameters can be determined in the commissioning mode that are used in the operation mode of the combustion appliance. In the present application, flue gas oxygen values are determined during the commissioning mode and stored in a memory of the combustion appliance. Said flue gas oxygen values are used for the operation of the combustion appliance in the operation mode. A control unit of the combustion appliance switches from the commissioning mode to the operation mode after all relevant parameters and / or components are determined and / or set.

[0015] The determination of the at least one Wobbe value and / or calorific value can be done when the combustion appliance is operated in the commissioning mode and / or when the combustion appliance is operated in the operation mode. In both modes the combustion appliance can be controlled on the determined at least one Wobbe value and / or calorific value.

[0016] The Wobbe value is an indicator of the interchangeability of fuel gases. It is used to compare the combustion energy output of different composition fuel gases in an appliance. If two fuels have identical Wobbe values, then for given pressure and valve settings, the energy output will also be identical or will be considered as identical.

[0017] The gross Wobbe index or value is defined as the volume-basis gross calorific value, at specified reference conditions, divided by the square root of the relative density at the same specified metering reference conditions. In common usage, and in the absence of any other qualifier, the term Wobbe index is taken to mean the quantity that is identified here as gross Wobbe index or value (Definition 3.5 ISO 6976:2016).

[0018] The net Wobbe index or value is the volume-basis net calorific value, at specified reference conditions, divided by the square root of the relative density at the same specified metering reference conditions (Definition 3.6 ISO 6976:2016). Both Wobbe indices can be used for the purpose of comparison, as long as the same type of index is used for the respective comparison.

[0019] The Wobbe index or value can be expressed in MJ / Nm3according to ISO 13443:1996.

[0020] An operation mode is a mode of the combustion appliance which is present after the commissioning is finalized. The operation mode can include an ignition phase, in which the combustion appliance is ignited, and a heating phase, in which the combustion appliance provides heat to be used by at least one consumer. Additionally, the operation mode can comprise a switch-off phase, in which the combustion appliance is switched off so that the combustion appliance for example can be maintained. .

[0021] In the operation mode the parameters determined and set in the commissioning mode are used to operate the combustion appliance. Additionally, in particular, merely in the operation mode, in particular in the heating phase of the operation mode, the outputted heat of the combustion appliance outputs is used in different kind of applications like for central heating and / or domestic water heating. Further application fields of the combustion appliance can be to provide process heating. Process heating is used in commercial use for industrial processes that needs heat. In said case a constant heat output has to be provided. In the ignition phase of the operation mode the air and fuel gas mixture is ignited in the combustion chamber on the burner surface by the ignition electrode.

[0022] The combustion appliance can be in a standby mode in which the combustion appliance is switched on, but the burner is not working. Alternatively, the combustion appliance can be in a commissioning or in an operation mode in which it has a specific power output. At normal operation the boiler sets its power output by modulation. Controlling the combustion appliance covers all different modes, including the phases that can occur during the respective mode.

[0023] A failure state of the combustion appliance is a combustion appliance state in which a combustion appliance component malfunctions so that the combustion appliance does not operate as expected. Additionally or alternatively a combustion appliance failure state is a state in which inadequate conditions, e.g. insufficient fuel or air, are present so that the burner does not start and thus the combustion appliance does not operate as expected. Further, the ignition can be loud and rough due to suboptimal incomplete combustion conditions in a failure state of the combustion appliance. Thus, a failure state covers a failed ignition or no ignition. For the case that a failure state is determined, a combustion appliance starting process, or the operation process of the combustion appliance is aborted and / or the combustion appliance can be blocked. Further, a failure state can be present when the measured air to fuel gas mixture does not correspond to the expected air to fuel gas mixture so that the combustion appliance does not operate as expected. Another advantage of the invention is that by considering the oxygen value a commissioning time in case of ignition failure is reduced.

[0024] A failure free state of the combustion appliance is a combustion appliance state in which the combustion appliance operates as expected.

[0025] The combustion appliance, in particular a data processing unit of the combustion appliance, can determine the flue gas oxygen value which is a measure for air to fuel gas ratio. The data processing unit can control the combustion appliance on the basis of the determined air to fuel gas ratio. Thus, the combustion appliance can be easily controlled by measuring the flue gas oxygen value.

[0026] The oxygen value, in particular a flue gas oxygen value, is measured by the oxygen sensor. The oxygen sensor can measure the partial oxygen pressure and uses this to determine the oxygen concentration in the gas to be measured, wherein the measured concentration can be outputted. Specifically, the oxygen sensor can measure the oxygen volume percentage of oxygen in the gas being analyzed. The oxygen sensor can be an unheated or a heated oxygen sensor. Alternatively, the oxygen sensor can be a fast light off oxygen sensor or planar sensor, which uses layers of zirconia and alumina bonded together to allow a much faster warm up. The oxygen sensor can also be air fuel ratio and wideband sensors.

[0027] The oxygen sensor can be arranged downstream the burner. Additionally or alternatively, the oxygen value of a non-combusted gas, for example of the air and fuel gas mixture or air alone if no fuel is inserted can be measured. In this case the oxygen value can be measured in the combustion chamber before the burner combusts the air and fuel gas mixture and / or in a part of the gas flow path being upstream of the combustion chamber in which the gas mixture comprising air and fuel gas flows.

[0028] A heated oxygen sensor can comprise or be thermally connected to an electrical heating element. The electrical heating element may be operable to heat the heated oxygen sensor in dependent on a heating signal, allowing to operate the electrical heating element to heat or not heat the oxygen sensor. The heating element can be a wire and / or resistor that provides heat when it is energized.

[0029] The oxygen sensor can be arranged in the combustion chamber. Thus, the oxygen sensor can easily measure the flue gas oxygen value and / or can quickly response to oxygen value changes in the combustion chamber. Additionally or alternatively, the oxygen sensor can be arranged upstream of the burner. This is possible as the method does not need the flue gas to detect a change in oxygen. The oxygen sensor can be heated and calibrated before the oxygen sensor can be used. The data processing device initiates the oxygen sensor heating and calibration.

[0030] The data processing device initiates the oxygen sensor calibration and the purging of the combustion chamber. Thereto, the data processing device transmits control signals to the corresponding components of the combustion appliance. Specifically, the data processing device can transmit the control signal to a sensor data processing unit of the oxygen sensor. The control signal can comprise the information that the oxygen sensor shall calibrate. Additionally, the data processing device transmits a control signal to the fan of the combustion appliance. Said control signal ensures that the fan runs at a predefined fan speed for a defined time. As purging within the meaning of this application, it is understood that combustion products, in particular flue gas or fuel, or fuel, in particular fuel gas, are flushed out of the combustion chamber. During the purging the fuel valve is closed so that it is ensured that no fuel flows into the combustion chamber and that only air is inside the combustion chamber. Additionally, it is realized that a calibration can be easily performed during the purging as the oxygen concentration in air is known. Thus, the oxygen sensor can be easily calibrated.

[0031] During the calibration a sensing element of the oxygen sensor detects an oxygen value. Said oxygen value is assigned the known oxygen concentration in air. This assignment can be performed by the sensor data processing unit of the oxygen sensor.

[0032] According to an embodiment the purging of the combustion chamber can be a postpurging, which is performed after a heat request is ended and / or which is performed when a burner operation is stopped after a burner time-period expired. During postpurging the burner is not operated so that the flue gas arranged within the combustion chamber is flushed out the combustion chamber. The data processing unit can initiate the post-purging after each heat request is satisfied and thus ended. Thus, the calibration can be performed during purging, which is done after heat request is ended. In other words, the calibration can be easily integrated in the workflow of a combustion appliance. Specifically, there is no interruption of the workflow of the combustion appliance for realizing the calibration of the sensor.

[0033] The data processing unit can initiate the calibration after a predetermined time after the post-purging is initiated and / or finalized. This is done to ensure that the flue gas is flushed out the combustion chamber before the oxygen sensor is calibrated. The calibration process can end at the same time as the post-purging. Alternatively, it is possible that the calibration of the oxygen sensor ends later than the post-purging of the combustion chamber.

[0034] The burner time-period is a time-period or length of time, for example 24h, after which the data processing device has to determine whether a flame is still present. In other words, the workflow of a combustion appliance is not disturbed by the calibration of the oxygen sensor. The data processing device can determine during the operation of the combustion appliance whether a calibration time interval is expired during which the oxygen sensor has to be calibrated. The calibration time interval can be between 24h and 48h. The calibration time interval can be lower than a mandatory time interval that can be provided by a sensor manufacturer. After expiry of the mandatory time interval, the burner needs to be stopped so that the situation can happen that the burner is stopped even though user heat request is not satisfied. Thus, by using the calibration time interval such situation can be prevented.

[0035] The data processing device can prevent said situation by initializing the calibration of the oxygen sensor when a burner operation is stopped because the calibration time interval expired. In this case the calibration is performed during the combustion chamber is postpurged. Thus, the calibration is done after a burner operation is stopped, that means, there is no combustion within the combustion chamber.

[0036] Additionally or alternatively, the data processing device can prevent such a situation by initializing the calibration of the oxygen sensor when the combustion appliance is in a standby-mode and the calibration time interval is expired. In this case the calibration is performed during a pre-purging of the combustion chamber, which is performed before a burner operation starts. By pre-purging the combustion chamber it is ensured that no undesired fuel either from the previous combustion process or due to a damage of the fuel valve is in the combustion chamber.

[0037] The data processing device can initialize the calibration of the oxygen sensor when the data processing device determines that the oxygen sensor is not calibrated when the combustion appliance is started. In that case the data processing device ensures that the calibration is performed during a pre-purging of the combustion chamber. In the end the data processing device can determine dependent on the calibration state of the oxygen sensor and / or the combustion appliance operation whether the oxygen sensor has to be calibrated or not.

[0038] The oxygen sensor can be heated during the calibration. Specially, the calibration can only be performed when the oxygen sensor, in particular the sensing element of the oxygen sensor is heated up. The oxygen sensor can comprise a heating element, in particular in the sensor data processing unit, for heating the sensing element. The oxygen sensor can cooperate with an electrical heating element which is thermally connected to the sensing element of the oxygen sensor. The electrical heating element may be operable to heat the sensing element of the oxygen sensor in dependent on a heating signal, allowing to operate the electrical heating element to heat or not heat the sensing element of the oxygen sensor.

[0039] The data processing unit can initiate a pre-purging of the combustion chamber when the oxygen sensor starts to heat up. The oxygen sensor is calibrated after it is heated up wherein the time for pre-purging is chosen such that the oxygen sensor can both be heated-up and calibrated.

[0040] By considering the heating status of the oxygen sensor it is possible that the data processing device determines whether the heating of the oxygen sensor is started and whether the calibration time interval is expired. The data processing device initiates a pre-purging of the combustion chamber when the heating of the oxygen sensor is not started and / or the calibration time interval is expired. Thus, it is not necessary that the oxygen sensor is always kept heated, but it is possible to heat up the sensor when a heat request is existent so that energy for heating the oxygen sensor can be saved.

[0041] According to an embodiment the heating up start of the oxygen sensor depends on a predetermined time schedule. The time schedule can comprise information when a combustion appliance has to fulfill a heat request. Additionally or alternatively the time schedule can comprise an information which at least one combustion appliance in a cascade of several combustion appliance has to fulfill a heat request. By having said information the data processing device can control the heating up and calibration of the oxygen sensor of the respective combustion appliance or combustion appliances. Specifically, the data processing unit can ensure that the oxygen sensor is heated up and / or the pre-purging of the combustion chamber is initiated before a heat request is to be considered. Thus, a time loss can be prevented, and the demanded heat can be provided soon. In the end, by providing a customizable oxygen sensor calibration schedule it is possible to optimize energy efficiency of the oxygen sensor.

[0042] According to an aspect of the invention a data processing device comprising means for carrying out an inventive method is provided. The data processing device receives the flue gas oxygen value from the oxygen sensor of the combustion appliance.

[0043] The data processing device can comprise at least one processor or be a processor. The data processing device can be part of a, printed circuit board, in particular a printed circuit board assembly, and have different portions executing different functions. The processor can have an internal memory.

[0044] Additionally, a computer program product is provided, which, when the program is executed by a computer, in particular a data processing unit, cause the computer, in particular the data processing unit, to carry out the inventive method. Furthermore, a computer readable data carrier having stored thereon the computer program product or data carrier signal carrying the computer program product is provided.

[0045] The fuel valve, in particular fuel gas valve, can be a pneumatic gas valve. In said case, the fuel gas flow automatically changes when an air flow changes due to e.g. a different fan speed. The fuel valve can be arranged downstream a fuel gas source and upstream the throttle unit, in particular the throttle element.

[0046] The combustion appliance can comprise a mixture device in which the fuel, in particular fuel gas, and the air are mixed before the mixture enters the combustion chamber of the combustion appliance. In an alternative embodiment the fuel and air are not mixed before the combustion chamber but in the combustion chamber.

[0047] The combustion appliance can comprise a throttle unit that is arranged fluidically downstream of the fuel valve, wherein the data processing device is connected with the throttle unit, in particular a throttle motor.

[0048] The throttle unit comprises a throttle element for controlling a throttle opening cross section through which the fuel gas flows. The throttle unit has the advantage that the fuel gas flow coming from the fuel gas valve can be controlled independent of the fan speed so that it is possible to remain the measured oxygen value on a constant level. The data processing device can control the throttle unit and / or the fan and / or the fuel valve dependent on the measured at least one oxygen value.

[0049] Fluidically downstream means that the throttle unit as a hole component is arranged outside the fuel valve, in particular the fuel gas valve, and adjacent to the fuel valve. Alternatively, fluidically downstream means that at least a part of the throttle unit, in particular the throttle element, can be arranged inside the fuel valve, in particular a fuel gas valve. However, said throttle element is arranged inside the fuel valve such that it receives the fuel, in particular the fuel gas that passed a valve element of the fuel valve, in particular the fuel gas valve. The fuel valve, in particular the fuel gas valve, can be a pneumatic valve, in particular a pneumatic gas valve. The fuel valve, in particular the fuel gas valve, can also be a controllable pneumatic valve, or a stepper valve, or a modulator valve. In said fuel valve the fuel flow automatically changes when an air flow changes due to e.g. a different fan speed. The fuel valve can be arranged downstream a fuel gas source and upstream the throttle unit, in particular the throttle element. The data processing device can be data connected with the throttle unit. Additionally or alternatively the throttle unit can be attached on the fuel gas valve. Thus, a compact unit comprising the fuel gas valve and the throttle unit is provided.

[0050] The modulator valve, or modulating valve is a control valve that can be fully open, fully closed, or in-between open and closed allowing a partial flow. The modulator valve is automated with an electrical actuator in combination with the fuel valve. The electrical actuator is configured to carry out modulating control, often referred to as a digital positioning system. The electrical actuator is thus able to accurately position the fuel valve anywhere between the fully open and the fully closed position. Typically, modulation is achieved using a control loop system and a positioning circuit board placed in the actuator. The actuator using a feedback system to give feedback on the fuel valve’s position to an operator. The modulation is achieved by comparing the input position (desired position) to the physical position of the output shaft (actual position). The output shaft’s location is fed back to the positioning circuit board by a potentiometer that is driven by the output shaft. The positioning circuit board then compares the two positions, and if there is a difference it considers this an ‘error’. To correct the error, the control unit will operate the modulator valve until it reaches the desired position. The control signals are typically either 0-10 V DC or 4-20 mA. A 0 V DC or 4 mA signal completely closes the fuel valve while a 10 V DC or 20 mA completely open the fuel valve. Any signal between these would cause a corresponding partially opened or closed position. An example would be a 6mA signal that would result in a 12° turn.

[0051] The stepper valve comprises a stepper motor, also known as step motor or stepping motor, which is an electrical motor that rotates in a series of small angular steps. The stepper motor thus divides a full revolution into a number of equidistant steps. The stepper motor consists of several "toothed" electromagnets arranged as a stator around a central rotor. These electromagnets are activated by an external driver circuit or a microcontroller. Each step rotates the shaft through a fixed angle. The circular arrangement of electromagnets is divided into groups referred to as phases. A stepper motor can be precisely rotated through a specific angle by activating the electromagnets one after the other.

[0052] The controllable pneumatic valve is a valve wherein a fluid flow rate is controlled by varying the size of the flow passage via a restrictor. In an automatic control valve, the restrictor is directed by a signal from an actuator.

[0053] Typical examples of controllable pneumatic valves are solenoid valves, in particular proportional solenoid valves. The proportional control solenoid valve utilizes a solenoid as an actuator for variable valve positioning. In a normally closed solenoid control valve, with zero current fed to the coil, the spring pushes the plunger downwards to a fully closed position. Applying current to the coil generates a magnetic field to move the plunger upward against the return spring. At 100% duty cycle, power is fully fed to the solenoid and the solenoid valve is completely open. The term duty cycle describes the proportion of on time to the cycle duration interval in a pulse-width modulation for controlling a load. Pulse-width modulation in other words is a method of controlling the average power or amplitude delivered by an electrical signal. A low duty cycle corresponds to low power because the power is off for most of the time. Duty cycle is expressed in percent, with 100% being fully on. Duty cycles between 0 to 100 percent range proportionally change the flow of the valve. For example, a duty cycle of 50% fed to the solenoid moves the spring and the plunger to 50% of the operating range.

[0054] In the figures, the subject-matter of the invention is schematically shown, wherein identical or similarly acting elements are usually provided with the same reference signs.

[0055] Figure 1 an overview of a combustion appliance according to the invention.

[0056] Figure 2 a structure of a data processing device.

[0057] Figure 3 a flow chart of an operation method executed by the data processing device according to a first embodiment.

[0058] Figure 3a a flow chart of an operation method executed by the data processing device according to a second embodiment.

[0059] Figure 4 a method for determining a throttle element position according to the first embodiment.

[0060] Figure 4a a method for determining a throttle element position according to the second embodiment. Figure 5 a method for determining a flue gas oxygen values table in the commissioning mode according to the first embodiment wherein the table is used in an operation mode of the combustion appliance.

[0061] Figure 5a a method for determining a flue gas oxygen values table in the commissioning mode according to the second embodiment wherein the table is used in an operation mode of the combustion appliance.

[0062] Figure 6 a diagram showing a flue gas oxygen curve dependent on a power state of the combustion appliance according to the first embodiment.

[0063] Figure 6a a diagram showing a flue gas oxygen curve dependent on a power state of the combustion appliance according to the second embodiment.

[0064] Figure 7 a flow chart relating to an operation of the combustion appliance in the operation mode according to the first embodiment.

[0065] Figure 7a a flow chart relating to an operation of the combustion appliance in the operation mode according to the second embodiment.

[0066] Figure 8 a flow chart relating to a transition method to prepare the combustion appliance to switch to a standby mode or to stop the combustion appliance according to the first embodiment.

[0067] Figure 8a a flow chart relating to a transition method to prepare the combustion appliance to switch to a standby mode or to stop the combustion appliance according to the second embodiment.

[0068] Figure 9 a flow chart showing the method for setting the starting behavior of the combustion appliance according to the first embodiment.

[0069] Figure 9a a flow chart showing the method for setting the starting behavior of the combustion appliance according to the second embodiment.

[0070] Figure 10 an overview of a system comprising several combustion appliances in a state in which all combustion appliances are in an operation mode.

[0071] Figure 11 an overview on a system comprising several combustion appliances in a state in which some combustion appliances are in a standby mode.

[0072] Figure 12 a flow chart for detecting blockage in flue gas path of a combustion appliance.

[0073] Figure 13 a diagram illustrating how blockage in the flue gas path can be determined according to a first variant.

[0074] Figure 14 a diagram illustrating how blockage in the flue gas path can be determined according to a second variant.

[0075] Figure 15 a diagram illustrating how blockage in the flue gas path can be determined according to a third variant. Figure 16 a flow chart illustrating how a combustion appliance failure state is determined.

[0076] Figure 17 a diagram showing different states of the combustion appliance during a ignition phase of the combustion appliance,

[0077] Figure 18 a calibration of the oxygen sensor for a situation in which the oxygen sensor is always heated.

[0078] Figure 19 a calibration of the oxygen sensor for a situation in which the oxygen sensor is not constantly heated.

[0079] Figure 20 a calibration of the oxygen sensor for a situation in which the oxygen sensor is heated for a predetermined time.

[0080] Figure 1 shows an overview of a combustion appliance 1 according to the invention. The combustion appliance 1 comprises a fan 4, a fuel gas source 11 for providing fuel gas and a fuel valve 5, in particular a fuel gas valve, for controlling the fuel gas flow. The fuel valve 5 is a pneumatic valve so that the fuel flow depends on the fan speed. The combustion appliance 1 also comprises a throttle unit 6 that is located downstream the fuel valve 5.

[0081] The throttle unit 6 controls the fuel flow, in particular the fuel gas flow, coming from the fuel valve 5. The throttle unit 6 comprises a throttle motor 22 and a throttle element 21 shown in figure 2. The throttle motor 22 changes the position of the throttle element 21 . The throttle element 21 delimits a throttle opening cross section through which the fuel, in particular fuel gas, can flow. Thus, the fuel flow that passes through the throttle unit 6 depends on the position of the throttle element 21. The throttle unit 6 is electrically connected with a data processing unit 9 of the combustion appliance 1 as is indicated with dotted line in figure 1 .

[0082] The throttle element position depends on the instruction that is received from the data processing unit 9. For setting a throttle element position the data processing unit 9 transmits a throttle position signal P to the throttle unit 6, in particular the throttle motor 22. The throttle motor 22 changes the position of the throttle element 21 according to the received throttle position signal P. In a non-shown embodiment, there is no bidirectional communication between the throttle unit 6 and the data processing unit 9 but the data processing unit 9 transmits a throttle position signal P to the throttle unit 6. That means in said case the data processing unit 9 does not receive any response from the throttle unit 6. The data processing device 9 comprises a processor and / or can be used to set the power state of the combustion appliance 1 . Thereto, the data processing device 9 sends at least one operation signal S1-S4 to the fan 4 to set the fan speed. In particular, the data processing device 9 can set the combustion appliance 1 to operate in a minimum power state, a maximum power state or a power state that is between the maximum and minimum power state.

[0083] The combustion appliance 1 also comprises a manifold 13. The manifold 13 is arranged upstream of a burner 7 of the combustion appliance 1 and is used to mix the fuel, in particular the fuel gas, passing the throttle unit 6 with air provided by the fan 4. The combustible mixed gas is burned in a combustion chamber 18 of the combustion appliance 1 by the burner 7. The combustion appliance 1 comprises a heat exchanger 12 that surrounds the combustion chamber 18 and that is used to transfer the heat to a liquid, in particular water, that is used for a central heating and / or for domestic hot water. The flue gas leaves the combustion chamber 18 via an exhaust flue path 17.

[0084] The combustion appliance 1 comprises an oxygen sensor 8 that is arranged in the combustion chamber 18. The oxygen sensor 8 is used to measure a flue gas oxygen value. In other words, the oxygen sensor measures the oxygen concentration in the flue gas when a combustion occurred in the combustion chamber 18. In a non-shown embodiment, the oxygen sensor 8 measures the oxygen concentration in air. The data processing device 9 is electrically connected to the oxygen sensor 8 and receives the measured flue gas oxygen values. An air to fuel gas ratio can be determined on the basis of the received flue gas oxygen value. The data processing device 9 can control the combustion appliance 1 on the basis of the determined airto fuel gas ratio in an operation mode of the combustion appliance.

[0085] Figure 2 shows a structure of the data processing device 9. The data processing device 9 comprises a comfort unit portion 27, a safety unit control portion 28 and a throttle unit control portion 26. The comfort unit portion 27 is electronically connected to a temperature sensor 29 measuring a room temperature, which is used to determine a heat request. Thus, the comfort unit portion 27 can exchange data with the temperature sensor 29. In particular, the comfort unit portion 27 receives temperature values measured by the temperature sensor 29. The comfort unit portion 27 can control the heat output of the combustion appliance 1 dependent on the temperature value received from the temperature sensor 29. The throttle unit control portion 26 is electronically connected to the throttle unit 6. Thus, the throttle unit control portion 26 exchanges data with the throttle unit 6 or is configured to only transmit data to the throttle unit 6. In particular, the throttle unit control portion 26 can transmit a control signal to the throttle unit 6 to control the fuel flow, in particular fuel gas flow, that flows through the throttle unit 6. The throttle unit 6 comprises the throttle motor 22 and the throttle element 21. The throttle motor 22 controls the position of the throttle element 21 and thus the throttle opening cross section through which the fuel, in particular the fuel gas, can flow. The throttle motor 22 controls the position of the throttle element 21 on the basis of the control signal that is received from the throttle unit control portion 26.

[0086] The safety unit control portion 28 is electronically connected to the oxygen sensor 8. Thus, the safety unit control portion 28 exchanges data with the oxygen sensor 8. In particular, the safety unit control portion 28 receives flue gas oxygen values 01-04 that are received by the oxygen sensor 8. The oxygen sensor comprises a sensing element 19 and a sensor data processing unit 20 that receives the values measured by the sensing element 19. The sensor data processing unit 20 is electronically connected to the safety unit control portion 28.

[0087] The combustion appliance 1 comprises a heating element 34 for electrically heating the sensing element 19. In the shown embodiment the heating element 34 is an integral part of the oxygen sensor 8. The heating element 34 can comprise or be a wire and / or resistor that outputs heat when it is energized. The sensor data processing unit 20 controls when the heating element 34 is energized, wherein the control is indicated by the dotted line in Fig. 2. In a non-shown embodiment, the heating element 34 can be a component that is not an integral part of the oxygen sensor 8 but is, in particular partly, arranged outside the oxygen sensor 8.

[0088] Figure 3 shows a flow chart of a method executed by the data processing device 9 according to a first embodiment. The method is explained below by referring to the figures 1 and 2.

[0089] In a first step G1 the data processing device 9 is powered-up. This is usually done when the combustion appliance 1 is started. In a second step G2 the data processing device 9 checks whether the combustion appliance 1 comprises an oxygen sensor 8. Thereto, it is checked whether the safety control portion 28 can communicate with the oxygen sensor 8. If this is not the case, it is determined in the third step G3, that the combustion appliance 1 is merely pneumatically controlled. That means, the throttle element position is not changed during the operation of the combustion appliance 1. In other words, the throttle element position is set manually by the installer. So, the third step G3 determines whether the combustion appliance 1 can be controlled as a gas adaptive combustion appliance 1. The determination in G3 thus means that the combustion appliance 1 comprises a traditional pneumatic gas valve - and therefore traditional pneumatic control (definition 3.1.201.22 of EN 12067-2:2022, 3.117) and uses CO2, CO, and 02 readings that are taken using a combustion analyser during commissioning. These readings guide the installer while manually adjusting the screws on the gas valve. In case the combustion appliance 1 comprises an oxygen sensor 8, it is determined in step G2 that the system has an adaptive combustion control function (definition 3.1.201.23 of EN12067-2:2022, 3.117). By adaptive combustion control function is meant a control function, intended to maintain lambda constant in a range AA or within pre-determined 02 boundaries (as shown in fig. 6) by adapting the flow of gaseous fuel and / or the flow of air and / or other physical quantities to compensate changes in input parameters relevant for the combustion process. The determination in G2 is thus that the combustion appliance 1 is a gas adaptive combustion appliance 1.

[0090] If the data processing device 9 determines in the second step G2 that the combustion appliance 1 comprises an oxygen sensor 8, a start position for the throttle element is initialized in a fourth step G4. Thereto, the data processing device transmits a throttle position signal P to the throttle motor 22, which sets the position of the throttle element dependent on the throttle position signal P to an initial position. This initial position can be predetermined or can correspond to a throttle element position that is determined in a previous operation of the combustion appliance 1. Alternatively, this initial position can be a fixed initial throttle element position which is the same at every start of second step G2. Alternatively, this initial position can be a position that is not known but that corresponds to the actual current throttle element position.

[0091] For the non-shown embodiment in which there is no bidirectional communication between the data processing device 9 and the throttle unit 6, the data processing device 9 changes the position by activating coils on the throttle motor 22 which results in fixed steps. There is no position information present. To set the throttle motor 22 into the initial position the throttle unit control portion 26 sends a number of steps to the throttle motor 22 that is greater than the real range that the throttle motor 22 can travel. Because the range is greater than a possible range the throttle motor 22 and / or the throttle element 21 reaches the end of the range and is now in a known position. From this position a step counter or bookkeeping is kept. That results in a known position of the throttle element 21 by the data processing device 9.

[0092] Alternatively, the actual position of the throttle element 21 is assumed to be appropriate for further operation. E.g., after commissioning, the actual position of the throttle element 21 may usually be appropriate as the gas quality will usually not have changed severely between commissioning and ignition. Also, after a previous operation in which heat is delivered, the position of the throttle element 21 may be assumed to be appropriate for further operation, irrespective of whether the actual position can be retrieved or not.

[0093] In the next fifth step G5 the oxygen sensor 8 is calibrated. The calibration is necessary as day-to-day variations of the ambient conditions influence the flue gas oxygen value measured by the oxygen sensor 8. The calibration can occur at different times. The calibration is explained below with respect to fig. 18 to 20.

[0094] In a sixth step G6 the data processing device 9 checks whether the combustion appliance 1 is commissioned. If not, a seventh step G7 is initialized by the data processing device 9. In the seventh step G7 the starting behavior of the combustion appliance 1 is set. The method for setting the start of the combustion appliance depends on the fuel gas quality. Said method is explained below more in detail with referring to figure 9.

[0095] In an eighth step G8 the data processing device 9 sets a position of the throttle unit 6. This setting is useful as the gas quality can change so that the throttle unit 6 is not set correctly. The setting of the throttle unit 6 is explained below more in detail when figure 4 is described.

[0096] Afterwards, in a nineth step G9 the data processing device generates a boundary table comprising flue gas oxygen values. The generated table is used when the combustion appliance 1 is operated in an operation mode, in particular in the ignition phase of the combustion appliance and / or in the heating phase of the combustion appliance for providing heat. The table generation is explained below when figure 5 is explained.

[0097] After the boundary table is generated, a sensor heating manager can be executed in a tenth step G10. Additionally in an eleventh step G11 a sensor calibration manager and in a twelfth step G12 a throttle starting positioning manager can be executed. The sensor heating manager ensures that the sensor heating, i.e. the heating of the sensing element 19 is turned on or off. The sensing element 19 can be electrically heated.

[0098] . The calibration starts when the oxygen sensor is sufficiently heated and the oxygen sensor remains heated during the calibration. The calibration takes a few seconds; however, heating may take a few minutes. During operation of the combustion appliance 1 there are moments where no heat demand is expected, this means, the heating can be turned off resulting in energy savings.

[0099] The sensor calibration manager can calibrate the oxygen sensor 8 in the eleventh step G11 to prevent discomfort for the user. The data processing device 9 ensures that each 72 hours the oxygen sensor 8 is calibrated. By tracking a calibration timer, the most optimal moment can be found. A calibration is done in air, wherein the percentage of oxygen in air is known. The calibration can be done in a pre-purge and / or post-purge process.

[0100] The throttle starting positioning manager checks the throttle element position in the twelfth step G12 during burning. If the fuel gas quality changes and a correction of the throttle element position is needed, the throttle starting positioning manager detects the change and stores the corrected throttle element position or change. The next burner start will be done by using the corrected throttle element position. The stored throttle element position is used to initialize the combustion appliance 1 in the fourth step G4 discussed above. The stored throttle element position is also used for the next start without having a power cycle in the first step G1 . In an alternative embodiment, the stored throttle element position is not used for the next start, but the next start starts with first step G 1 .

[0101] The throttle starting positioning manager, the sensor heating manager and the sensor calibration manager can be executed after the ninth method step G9. Additionally, said managers can be executed in cases after it is determined in the sixth step G6 that the combustion appliance has been commissioned. In particular, the managers can be executed before it is determined in a fourteenth step G14 whether a heat demand is present.

[0102] If no heat demand is present, the combustion appliance 1 is switched to a stand-by mode or is stopped in a fifteenth step G15. After the fifteenth step G15, it is possible to recheck in the fourteenth step G14, in particular after a predetermined time-period, whether a heat demand is present. This can be repeated until the combustion appliance 1 is stopped and deactivated and thus switched off. A time-period is a length of time and delimited by two time points.

[0103] If the data processing device determines in the fourteenth step G14 that a heat demand is present, a sixteenth method step G16 is initiated in which the starting behavior of the combustion appliance 1 is set. Likewise, to the seventh step G7 one part of the setting of the starting behavior can be to determine the fuel gas quality.

[0104] The sixteenth method step G16 corresponds to the seventh method step G7 explained above so that it is referred to said passages. The difference between the two method steps G7 and G16 is that in the seventh method step G7 the combustion appliance 1 is operated in the commissioning mode whereas in the sixteenth method step G16 the combustion appliance 1 is operated in the operation mode, in particular in the heating phase of the operation mode. In the heating phase of the operation mode, which is only possible after the commissioning mode is completed, the combustion appliance 1 provides a heat output that is used in an application like domestic hot water and / or central heating.

[0105] In a seventeenth method step G17 the data processing device 9 can control the throttle element position during a heat demand on the basis of the measured flue gas oxygen values. This is explained below more in detail together with figure 7.

[0106] In an eighteenth method step G18 the combustion appliance 1 is prepared for the standby mode or the stop of the combustion appliance 1. In particular, the combustion appliance 1 is prepared such that a restart of the combustion appliancel is done by using the correct parameters. The method step G18 is explained more in detail in figure 8.

[0107] Figure 3a shows a flow chart of an operation method executed by the data processing device according to a second embodiment. The method described in figure 3a is similar to the method described in figure 3. Thus, in the following, merely the differences of the method according to the second embodiment to the method according the first embodiment are described.

[0108] A difference of the method according to the second embodiment is that after the start position for the throttle element is initialized in the fourth step G4, the throttle element is moved to a position that corresponds to the first row in the Wobbe entry table in a further fourth step G4a. Afterwards, the oxygen sensor 8 is calibrated in the fifth step G5.

[0109] A further difference of the method according to the second embodiment is that the system does not comprise a throttle starting positioning manager so that the twelfth step G12 described for the method shown in figure 3 is not executed in the method according to the second embodiment.

[0110] The method according to the second embodiment executes a sensor heating by using a sensor heating manager in a tenth step G10. Additionally, the method according to the second embodiment executes sensor calibration by using the sensor calibration manager in the eleventh step G11 . However, in contrary to the method according to the first embodiment, the sensor heating manager and the sensor calibration manager are processed parallel to the steps G1-G9 and the steps G14-G18 in the method according to the second embodiment.

[0111] As discussed above in figure 3, in the method according to the first embodiment the sensor heating manager and the sensor calibration manager are processed after the ninth step G9 or after the sixth step G6.

[0112] Figure 4 shows a method for determining a throttle element position of the throttle unit 6 according to the first embodiment. Said figure shows the specifics of the eighth method step G8 shown in figure 3. In a first sub-step T1 the throttle element position setting is started. In a second sub-step T2, the data processing device 9 outputs a first operating signal S1 that causes that the combustion appliance 1 is operated in a maximum power state. Specifically, the first operating signal S1 is sent to the fan 4 to operate the combustion appliance 1 in the maximum power state. Additionally, the data processing device 9 receives a first flue gas oxygen value 01 measured by the oxygen sensor 8 when the combustion appliance is operated in the maximum power state. The throttle element position of the throttle unit 6 corresponds to the throttle element position that is set in the fourth method step G4.

[0113] Then, in a third sub-step T3 the data processing device checks whether the measured first flue gas oxygen value 01 fulfils a test condition. Specifically, the test condition comprises a check whether the first flue gas oxygen value 01 is arranged in a predetermined flue gas oxygen range assigned to maximum power state of the combustion appliance for a predetermined time-period. The predetermined flue gas oxygen band and the predetermined time-period can be saved in a memory of the combustion appliance 1 , in particular data processing device 9.

[0114] If the test condition is not fulfilled the throttle element position is adjusted in a fourth substep T4. The throttle element position can be automatically adjusted. Thereto, the data processing device 9, in particular the throttle unit control portion 26, sends out a throttle position signal P to change the throttle element position of the throttle element 21 and thus to change the fuel gas flowing through the throttle unit 6. The sub-steps T3 and T4 are repeated until the test condition is fulfilled. As soon as the test condition is fulfilled the throttle position of the throttle unit 6 is stored in the memory in a fifth sub-step T5.

[0115] In a sixth sub-step T6, the data processing device 9 outputs a second operating signal S2 that causes the combustion appliance 1 to operate in a minimum power state. Specifically, the data processing device 9 outputs the second operating signal S2 to the fan 4 to operate the combustion appliance 1 in the minimum power state. Additionally, the data processing device 9 receives a second flue gas oxygen value 02 from the oxygen sensor 8 when the combustion appliance is operated in the minimum power state. The throttle element position of the throttle unit 6 that is set when the combustion appliance 1 is operated in the minimum power state corresponds to the throttle element position that fulfils the test condition of the third method sub-step T3.

[0116] In a seventh sub-step T7 the data processing device 9 determines whether the received second flue gas oxygen value 02 fulfils a further test condition. Specifically, the further test condition comprises a check whether the second flue gas oxygen value 02 is arranged in a predetermined further flue gas oxygen range assigned to a minimum power state of the combustion appliance 1 for a predetermined further time-period. The predetermined further flue gas oxygen band and the predetermined further time-period can be saved in a memory of the combustion appliance 1.

[0117] If the test condition is not fulfilled the fuel valve 5 is adjusted in an eighth sub-step T8. The fuel valve 5 can be manually adjusted by an installer by adjusting an offset screw of the fuel valve 5. Alternatively, the fuel valve 5 can be automatically adjusted by the data processing device 9. The sub-steps T7 and T8 are repeated until the further test condition is fulfilled. After the further test condition is fulfilled, the throttle element position determination is finished. As is evident from figure 4, in the next step the boundary table is created in the nineth method step G9.

[0118] Figure 4a shows a method for determining a throttle element position according to the second embodiment. The method described in figure 4a is similar to the method described in figure 4. Thus, in the following, merely the differences of the method according to the second embodiment to the method according the first embodiment are described.

[0119] The method according to the second embodiment differs from the method shown in fig. 4 in that the throttle element position of the throttle element of the throttle unit 6 is not stored in the memory in a fifth sub-step T5. Thus, in the method according to the second embodiment no fifth sub-step T5 exists and the data processing device 9 outputs a second operating signal S2 in the sixth sub-step T6 directly after the test condition is fulfilled in the third sub-step T3.

[0120] The creation of the boundary table is shown in figure 5 more in detail. Figure 5 shows a method for determining a flue gas oxygen values table in the commissioning mode according to the first embodiment wherein the table is used in an operation mode of the combustion appliance. As is discussed above, the boundary table is created when the combustion appliance 1 is operated in the commissioning mode. Said table is used in an operation mode as is explained below more in detail.

[0121] In a first sub-step C1 the data processing device 9 starts with creating the boundary table. Said creation can only be done when the combustion appliance 1 is operated in the commissioning mode. In other words, the determined values of the table cannot be changed, when the combustion appliance 1 is operated in the operation mode. In the first sub-step C1 an upper and lower threshold 2, 3 is determined for the first flue gas oxygen value 01 and for the second flue gas oxygen value 02, respectively.

[0122] In a third sub-step C3 the data processing device 9 receives information about a third power state stored in a memory of the combustion appliance 1. The information can be stored in the memory in a second sub-step C2. Said second sub-step C2, namely the storing of data in the memory, can be conducted prior to the initialization of the first substep C1. The third power state is between the maximum power state and the minimum power state. In the third sub-step 03, the data processing device also sends a third operation signal S3, in particular to the fan, to cause the combustion appliance 1 to be operated in the third power state.

[0123] The data processing device 9 receives in a fourth sub-step C4 a third flue gas oxygen value 03. Additionally, the data processing device 9 determines in the fourth sub-step C4 an upper threshold value and a lower threshold value with respect to the third flue gas oxygen value 03. The measured third flue gas oxygen value 03 and the determined upper and lower threshold value are stored in a fifth sub-step C5.

[0124] In a sixth sub-step C6, the data processing device 9 determines whether the table is complete. If not, the data processing device sends a fourth operation signal S4 in a seventh sub-step C7, which results in that the combustion appliance 1 operates in power state that is between a maximum power state and a minimum power state, so that the combustion appliance 1 is operated in a fourth power state. The fourth power state differs from the first to third power state.

[0125] The data processing device 9 receives in a fourth sub-step C4, the fourth power state value from the memory likewise to the third power state from the memory, which comprises the data stored in the second sub-step C2, of the combustion appliance. In other words, the data processing device receives the fourth power state value and other power state values from the memory, which comprises the data stored in the second sub-step C2, in the third sub-step C3 or the seventh sub-step C7. Additionally, the data processing device 9 determines in the fourth sub-step C4 an upper threshold value and a lower threshold value with respect to the fourth flue gas oxygen value 04. The measured fourth flue gas oxygen value 04 and the determined upper and lower threshold value are stored in a fifth sub-step C5.

[0126] The sub-steps C4-C7 are repeated for all power states of the combustion appliance 1 that are stored in the memory as discussed above for sub-step C2. After the boundary table is created the boundary table creation method is finished in the eight sub-step C8.

[0127] A distance between the upper threshold 2 and the measured flue gas oxygen value can correspond to a distance between the lower threshold 3 and the measured flue gas oxygen value. Alternatively, it is possible that the determination of the upper and lower threshold is based on a value that depends on the measured flue gas oxygen value and a correction value. A distance between the upper threshold 2 and said value can correspond to a distance between the lower threshold 3 and said value. The correction value can be stored in an electrical memory or can be entered by an installer.

[0128] Figure 5a shows a method for determining a flue gas oxygen values table in the commissioning mode according to the second embodiment wherein the table is used in an operation mode of the combustion appliance. The method described in figure 5a is similar to the method described in figure 5. As is described below more in detail, the first and fourth sub-step C1a, C4a of the method according to the second embodiment differ from the method according to the first embodiment, which is the reason why the reference signs of said sub-steps differs from the reference signs of the sub-steps C1 and C4 used in fig. 5.

[0129] The data processing device 9 determines likewise to the method according to the first embodiment an upper and lower threshold value with respect to the first and second flue gas oxygen value 01 , 02 in the first sub-step C1a. Additionally, the data processing device 9 determines a further upper threshold value 2a and further lower threshold value 3a for the first flue gas oxygen value 01 and a further upper and lower threshold value 2a, 3a for the second flue gas oxygen value for the second flue gas oxygen value in the first sub-step C1a.

[0130] The data processing device 9 determines likewise to the method according to the first embodiment an upper and lower threshold value 2, 3 with respect to the third flue gas oxygen value 03 and all other flue gas oxygen values resulted from operating the combustion appliance in different power states in the fourth sub-step C4a. Additionally, the data processing device 9 determines a further upper threshold value and lower threshold value 2a, 3a for the third flue gas oxygen value and all other flue gas oxygen values resulted from operating the combustion appliance in different power states in the fourth sub-step C4a.

[0131] A distance between the upper threshold 2 and the measured flue gas oxygen value can correspond to a distance between the lower threshold 3 and the measured flue gas oxygen value. Alternatively, it is possible that the determination of the upper and lower threshold is based on a value that depends on the measured flue gas oxygen value and a correction value. A distance between the upper threshold 2 and said value can correspond to a distance between the lower threshold 3 and said value. The correction value can be stored in an electrical memory or can be entered by an installer. A distance between the further upper threshold 2a and the measured flue gas oxygen value can correspond to a distance between the further lower threshold 3a and the measured flue gas oxygen value. Alternatively, it is possible that the determination of the further upper and lower threshold is based on a value that depends on the measured flue gas oxygen value and a correction value. A distance between the further upper threshold 2a and said value can correspond to a distance between the further lower threshold 3a and said value. The correction value can be stored in an electrical memory or can be entered by an installer.

[0132] Additionally, the method according to the second embodiment comprises a tenth substep C10, which is conducted when it is determined in the sixth sub-step C6 that the table is completed. In the tenth sub-step C10 the data processing device 9 sets a commissioning flag indicating that the commissioning is done.

[0133] Figure 6 shows a diagram showing a flue gas oxygen curve dependent on a power state of the combustion appliance according to a first embodiment. Specifically, figure 6 shows curves that are determined on the basis of the values that are determined in the method shown in figure 5.

[0134] Figure 6 shows the dependency of flue gas oxygen values 01-04 from the power state of the combustion appliance. Specifically, figure 6 shows the first flue gas oxygen value 01 when the combustion appliance 1 is in the maximum power state and the second flue gas oxygen value 02 when the combustion appliance 1 is in the minimum power state. Further, figure 6 shows the third flue gas oxygen value 03 and the fourth as oxygen value 04 when the combustion appliance 1 is in at two intermediary power states in between the minimum power state and the maximum power state. Additionally, figure 6 shows upper thresholds 2 and lower thresholds 3. Each of the upper thresholds 2 and the lower thresholds 3 are assigned to one measured flue gas oxygen value. The upper and lower threshold curve defines a flue gas oxygen band that is used to control the combustion appliance as is explained more in detail in figure 7.

[0135] Figure 6a shows a diagram showing a flue gas oxygen curve dependent on a power state of the combustion appliance according to the second embodiment. In addition, to the upper thresholds 2 and the lower thresholds 3, figure 6a shows further upper thresholds 2a and further lower thresholds 3a. The further upper and lower thresholds are determined in the first and fourth sub-steps C1a, C4a shown in fig. 5a. Each of the further upper thresholds 2 and the further lower thresholds 3a are assigned to one measured flue gas oxygen value

[0136] The further upper and lower threshold curve defines a further flue gas oxygen band that is used to control the combustion appliance as is explained more in detail in figure 7a. As is evident from fig. 5a the further flue gas oxygen band is smaller than the flue gas oxygen band comprising the upper thresholds 2 and the lower thresholds 3. Additionally, the further flue gas oxygen band is a portion of the flue gas oxygen band.

[0137] Figure 7 shows a flow chart relating to a combustion control of the combustion appliance 1 in the operation mode according to a first embodiment. That means, the method steps are performed after the combustion appliance 1 is commissioned. Specifically, figure 7 shows the method sub-steps that are executed in the seventeenth method step G17 shown in figure 3.

[0138] In a first method step N1 the combustion control method is initiated by the data processing device 9. In a second sub- step N2 it is checked whether a burner off condition is present. Said burner off condition can result if there is no heat demand request and / or if a burner could not be started for a predetermined number of times. If the burner off condition is fulfilled, the combustion appliance 1 is prepared for a standby mode or a stop in the third sub-step N3. This transition process is shown in figure 8 more in detail.

[0139] If the data processing device 9 determines in the second sub-step N2 that the burner off condition is not reached, the oxygen sensor 8 measures the flue gas oxygen value in the combustion chamber 18 in a fourth sub-step N4. Specifically, the data processing device 9 receives the measured flue gas oxygen value in the fourth sub-step N4.

[0140] In a fifth sub-step N5 the data processing device 9 determines whether the measured flue gas oxygen value is within the flue gas oxygen range determined in the method shown in figure 5. Specially, the data processing device 9 determines whether the measured flue gas oxygen value is outside the flue gas oxygen range determined by an upper threshold curve and a lower threshold curve shown in figure 6. If this is not the case, the data processing device determines a normal operation and repeats the substeps N2-N5.

[0141] If the data processing device 9 determines in the fifth sub-step N5 that the measured flue gas oxygen value is outside the flue gas oxygen range, an adjusting process is started in a sixth sub-step N6. In said adjustment process it is checked in a seventh sub-step N7 whether the fan speed is above a fan threshold value. If this is not the case, the method is continued at the second sub-step N2.

[0142] If the fan speed is above a fan threshold, it is checked whether the throttle element position is kept constant for a predetermined time in an eighth step N8. If this is not the case the method is continued at the second sub-step N2. However, if the throttle element position is kept constant for a predetermined time, the present throttle element position is stored in the memory in a nineth step N9.

[0143] Figure 7a shows a flow chart relating to an operation of the combustion appliance in the operation mode according to a second embodiment. The method described in figure 7a is similar to the method described in figure 7.

[0144] The first sub-step N1 to fourth sub-step N4 are identical in both methods so that it is referred to the description of figure 7.

[0145] In a fifth sub-step N5a the data processing device 9 checks whether the flue gas oxygen value measured in the operation mode is lower than a predetermined value. The predetermined value can be the flue gas oxygen value that is obtained in the commissioning mode. Alternatively, the predetermined value can be dependent on the flue gas oxygen value that is obtained in the commissioning mode and a predetermined correction value that can be entered by the installer or that is stored in an electrical memory. In particular, the correction value can be added to the flue gas oxygen value obtained in the commissioning mode or subtracted from said flue gas oxygen value. Said value corresponds to the value described above in fig. 5, 5a that is the basis for the upper and lower threshold 2, 3 and / or the further upper threshold 2a, and further lower threshold 3a.

[0146] If the flue gas oxygen value measured in the operation mode is smaller than the predetermined value, the data processing device determines in a sixth sub-step N6a that the throttle unit, in particular the throttle element, is not arranged at its maximum position. Afterwards, the method is continued in a seventh sub-step N7a.

[0147] The method is also continued in the seventh sub-step N7a when the data processing device 9 determines in the fifth sub-step N5a that the measured flue gas oxygen value is not smaller than the predetermined value. In the seventh sub-step N7a the data processing device 9 checks whether flue gas oxygen value measured in the operation mode is arranged outside the band delimited by the upper threshold 2 and the lower threshold 3. Additionally, the data processing device 9 determines the seventh sub-step N7a whether the throttle element is arranged in its maximum position so that the opening cannot open any further. If at least one of the two conditions is not fulfilled, position the method is continued at the second substep N2. In said case the measured flue gas oxygen value is not arranged outside the band delimited by the upper threshold 2 and the lower threshold 3 and / or it is determined that the throttle element is not arranged at its maximum.

[0148] If the measured flue gas oxygen value is arranged outside the band delimited by the upper threshold 2 and the lower threshold 3 and if it is determined that the throttle element is not arranged at its maximum position, the data processing signal sends a control signal to a combustion appliance component in an eight sub-step N8a. The control signal can result in a change of the fan speed and / or a change of the throttle element position.

[0149] In a ninth step N9a, the data processing device 9 determines whetherthe flue gas oxygen value is arranged inside the band delimited by the further upper threshold 3a and the further lower threshold 3b. If the flue gas oxygen value is not arranged inside said band, the method is continued at the eight sub-step N8a. In said case the data processing device 9 amends the control signal resulting in a different fan speed and / or a different throttle element position.

[0150] If the data processing device 9 determines in the ninth sub-step N9a that the measured flue gas oxygen value is arranged inside the band delimited by the further upper threshold 2a and the further lower threshold 3a for a predetermined time, the method continues in the tenth sub-step N10a. Specifically, the method is continued in the tenth sub-step N10a only when the measured flue gas oxygen value is arranged inside the band delimited by the further upper threshold 2a and the further lower threshold 3a for the predetermined time.

[0151] Alternatively, the data processing device 9 determines in the ninth sub-step N9a whether the oxygen value is not arranged inside the band delimited by the further upper threshold 2a and the further lower threshold 3a for a predetermined further time. If the condition is fulfilled, the method is continued in the tenth sub-step N10a. In this case the situation is covered that the oxygen value does not get inside the defined band within the predetermined further time. Thus, the throttle element is arranged in the maximum position and after the further predetermined time lapsed, the ninth sub-step N9a results in a ‘yes’ The further time can be longer than the predetermined time that is also considered in the ninth sub-step N9a.

[0152] In the tenth sub-step N10a, the data processing device 9 determines whether the measured flue gas oxygen value is arranged outside the band delimited by the further upper threshold 2a and the further lower threshold 3a and whether the throttle element is arranged in its maximum position. If at least one of said two conditions is not fulfilled, the method continues in an eleventh sub-step N11a.

[0153] If both conditions are fulfilled, the data processing device 9 stores in a twelfth sub-step N12a that the throttle element is arranged in its maximum position. Afterwards, the method continues in the eleventh sub-step N11a.

[0154] In the eleventh sub-step N11a it is determined whether the fan speed is above a fan threshold value. If this is not the case, the method is continued at the second sub-step N2.

[0155] If the fan speed is above a fan threshold, it is checked whether the throttle element position is kept constant for a predetermined time in thirteenth sub-step N13a. If this is not the case the method is continued at the second sub-step N2. If it is determined in the thirteenth sub-step N13a that the throttle element is kept constant for a predetermined time, the method is continued in a fourteenth sub-step N14a.

[0156] In the fourteenth sub-step N14a the actual throttle element position is converted to a Wobbe value or calorific value. This can be done by using a table stored in the memory of the combustion appliance, wherein the table comprises information about Wobbe values or calorific values which are assigned to one throttle element position, respectively. Said table is discussed more in detail below in figure 9 and 9a.

[0157] In a fifteenth sub-step N15a, a fan speed or fan speed correction is determined dependent on the Wobbe value or calorific value that is determined in the fourteenth substep N14a. A further table can be stored in the memory of the combustion appliance, wherein the table comprises information about fan speed values or fan speed corrections which are dependent on the determined Wobbe value or calorific value. Thus, the fan speed changes with changing gas quality so that a basically constant heat output from the combustion appliance can be ensured even if the gas quality changes.

[0158] As is discussed above the data processing device 9 is configured such that it starts to control the combustion appliance components after the data processing device 9 determines that the measured flue gas oxygen value is arranged outside the band delimited by the upper threshold 2 and the lower threshold 3. After the control is initiated, the data processing device 9 controls the combustion appliance components, in particular fan and / or throttle element of throttle unit, such that the measured flue gas oxygen value is arranged inside the band delimited by the further upper threshold 2a and the further lower threshold 3a.

[0159] Figure 8 shows a flow chart relating to a transition process to switch the combustion appliance 1 from an operation mode to a standby mode or to stop the combustion appliance according to a first embodiment. Thereto, the switch off phase of the operation mode is initiated, which is described below.

[0160] In a first sub-step A1 , the transition process is initiated and therefore the combustion appliance is operated in the switch off phase of the operation mode. The transition process can be initiated when the burner off condition is reached as it is explained in figure 7.

[0161] In a second sub-step A2 the data processing device 9 causes that the burner 7 is stopped. Thus, no combustion occurs after the second sub-step A2. In a third sub-step A3, the throttle element is moved to a stored throttle element position. In a fourth substep A4 a post-purge process is performed. In the post-purge process the oxygen sensor can be calibrated by using the calibration manager described above. In a fifth sub-step A5 the transition process is finalized so that the combustion appliance can be switched to a standby mode or stopped in the fifteenth step G15 shown in figure 3.

[0162] Figure 8a shows a flow chart relating to a transition method to prepare the combustion appliance to switch from an operation mode to a standby mode or to stop the combustion appliance according to the second embodiment. The method according to the second embodiment differs from the method according to the first embodiment in that the method does not comprise the third sub-step A3, in which the throttle element is moved to a stored throttle element position. That means, the post-purge process of the fourth sub-step A4 is directly initialized after the burner is stopped in the third sub-step A3.

[0163] Figure 9 shows a flow chart for setting the starting behavior of the combustion appliance 1 according to a first embodiment. In a first sub-step W1 it is checked whether the fuel gas type or fuel gas quality is known that is supplied to the non-operating combustion appliance 1 . The fuel gas type or fuel gas quality can be specified by a value, in particular a Wobbe value and / or a calorific value. In the following, the flow chart is explained by referring to the Wobbe value. However, the starting behavior can be set by using the calorific value instead of the Wobbe value.

[0164] Alternatively, the first sub-step W1 may assume a certain fuel gas type or fuel gas quality and a corresponding, assumed Wobbe value and / or assumed calorific value. The assumed certain fuel gas type or fuel gas quality and corresponding, assumed Wobbe value and / or a calorific value may be those determined in an earlier commissioning operation and may be the same for every start after the earlier commissioning operation.

[0165] If the fuel gas quality or fuel gas type is not known and / or not assumed, in a second substep W2 a Wobbe value is taken from a Wobbe table that is stored in a memory. Specifically, the Wobbe value being arranged at the first position of the Wobbe table is taken. The Wobbe table can be structured such that the Wobbe value decreases with increasing position in the Wobbe table. The table is a two-dimensional table with rows and columns. With increasing position, it is meant that the Wobbe value arranged in a subsequent lower row is considered. The lowest Wobble value is found at the last position, i.e. last row, of the Wobbe table.

[0166] In a third sub-step W3 the throttle element position of the throttle unit 6 is determined. In particular, the throttle element position is determined that is assigned to the Wobbe value determined in the second sub-step W2. Alternatively, the throttle element position is determined that is assigned to the assumed Wobbe value.

[0167] In a fourth sub-step W4 the fuel gas and air mixture that is present in the combustion chamber of the combustion appliance 1 is ignited. In a fifth sub-step W5 the data processing device 9 that is assigned to the combustion appliance 1 determines whether a flame is present. In other words, in the fifth sub-step W5 it is determined whether the ignition was successful. The combustion appliance 1 can comprise a flame detector for detecting a flame and thus for determining whether the ignition is successful. In a sixth sub-step W6 the oxygen sensor 8 measures the oxygen value after the fuel gas and air mixture is ignited in the fifth sub-step W5. If the mixture is ignited, the oxygen sensor 8 will measure a flue gas oxygen value. Otherwise, the oxygen sensor 8 measures the oxygen proportion in the mixture.

[0168] If the data processing device 9 determines in the fifth sub-step W5 that a flame is present, the Wobbe value of the fuel gas and the throttle element position are known. Specifically, the Wobbe value corresponds to the Wobbe value that is assigned to the throttle element position in the Wobbe table. That means after the fifth step the fuel gas quality is known.

[0169] Additionally, it is checked in a seventh step W7 if the combustion appliance 1 is already commissioned. If this is the case, the method is continued in an eighth step W8 that corresponds to the seventeenth sub-step G17 shown in Fig. 3. If the data processing device 9 determines that the combustion appliance is not commissioned in the seventh step W7, the method is continued in a ninth sub-step W9 that corresponds to the eight step G8 shown in figure 3.

[0170] If the data processing device 9 cannot determine the presence of a flame in the fifth substep W5, the data processing device 9 checks whether a maximum number of ignition attempts are made in a tenth sub- step W10. If this is the case the data processing device aborts the ignition phase and can lock the combustion appliance 1 in an eleventh substep W11 .

[0171] If the maximum number of ignition attempts is not reached, the data processing device checks in a twelfth sub-step W12 whether the oxygen value measured in the sixth substep W6 is arranged within a predetermined oxygen range. If this is not the case, a new ignition is initiated in the fourth sub-step W4.

[0172] However, if the measured oxygen value is arranged in the predetermined range, the data processing device 9 reads out the Wobbe value that is assigned to the next position, i.e. next row, of the Wobbe table discussed in the second sub-step W2 in the thirteenth substep W13. In other words, the next lower Wobbe value is read out. In a fourteenth substep W14 it is checked whether the new table position from which the Wobbe value is read out is the last position, i.e. the last row, of the Wobbe table. That means, it is determined whether Wobbe table is at the final position. If this is the case, the data processing device 9 initiates the ignition in the fourth sub-step W4. If the new table position is not the last position, i.e. not the last row, the data processing device 9 determines the throttle element position that is assigned to the Wobbe value being in the newly determined position in a fifteenth sub-step W15. Additionally, the data processing device 9 receives the throttle element position that is saved in a memory in a sixteenth sub-step W16.

[0173] The data processing device 9 checks in a seventeenth sub-step W17 whether the saved throttle element position is greater than the throttle element position that is determined in the fifteenth sub-step W15. If the determined throttle element position is greater than the saved throttle element position, the method is continued in the fourth sub-step W4. If the throttle element position is not greater than the saved throttle element position, the sub-step method is continued in the thirteenth sub-step W13.

[0174] Figure 9a shows a flow chart showing the method for setting the starting behavior of the combustion appliance according to a second embodiment. The starting behaviour of the combustion appliance as discussed in fig. 9a is explained by referring to the Wobbe value. However, the starting behavior can be alternatively set by using the calorific value instead of the Wobbe value.

[0175] In a first sub-step W1a the data processing device 9 determines whether the combustion appliance has already been commissioned. This is the case if a commissioning flag is set.

[0176] If the combustion appliance is not commissioned, in a second sub-step W2 a Wobbe value assigned to a first row of a Wobbe is taken. The Wobbe table is stored in an electronic memory of the combustion appliance. The Wobbe table can be structured such that it comprises several rows containing Wobbe values. The Wobbe value decreases with increasing position of the row in the Wobbe table, i.e. with increasing row number. The table is a two-dimensional table with rows and columns. With increasing position, it is meant that the Wobbe value arranged in a subsequent lower row is considered. The lowest Wobble value is found at the last position, i.e. last row, of the Wobbe table.

[0177] The Wobbe value identified in the second sub-step W2a and its corresponding row position is stored in a database in a third sub-step W3a. In a fourth sub-step W4a the throttle element position of the throttle unit 6 is determined. In particular, the throttle element position is determined that is assigned to the Wobbe value determined in the second sub-step W2a. In a fifth sub-step W5a the throttle element of the throttle unit 6 is moved to the determined throttle element position and the method is continued with a sixth sub-step W6a.

[0178] If the data processing device 9 determines in the first sub-step W1a that the combustion appliance is commissioned, the data processing device 9 determines in a further first sub-step W1 b whether an unexpected flame loss has occurred during a heat demand, in particular during the previous heating operation, or not. Hereto, in the further first substep W1 b the data processing device 9 can, in particular, check the presence or value of a blocking code that has been written in a memory at such unexpected occurrence. If it is determined that such flame loss occured, the method is continued with the second sub-step W2a. If not, the method continues with the sixth sub-step W6a.

[0179] In the sixth sub-step W6a the fuel gas and air mixture that is present in the combustion chamber of the combustion appliance 1 is ignited. In a seventh sub-step W7a the data processing device 9 that is assigned to the combustion appliance 1 determines whether a flame is present. In other words, in the seventh sub-step W7a it is determined whether the ignition was successful. The combustion appliance 1 can comprise a flame detector for detecting a flame and thus for determining whether the ignition is successful.

[0180] In an eight sub-step W8a the oxygen sensor 8 measures the oxygen value after the fuel gas and air mixture is ignited or after an attempt to ignite in the sixth sub-step W6a. If the mixture is ignited, the oxygen sensor 8 will measure a flue gas oxygen value. Otherwise, the oxygen sensor 8 measures the oxygen proportion in the mixture. The eight sub-step W8a is done in parallel to at least the fourteenth sub-step W14a.

[0181] If the data processing device 9 determines in seventh sub-step W7a that a flame is present, the Wobbe value of the fuel gas and the throttle element position are known. Specifically, the Wobbe value corresponds to the Wobbe value that is assigned to the throttle element position in the Wobbe table. That means after the seventh sub-step W7a the fuel gas quality is known.

[0182] In a nineth sub-step W9a the data processing determines 9 whether a commissioning flag is set and thus the combustion appliance 1 is already commissioned. If this is the case, the method is continued in a tenth sub-step W10a. In the tenth sub-step W10a it is waited for a predetermined time, for example 10 s, so that the measured oxygen values stabilize. Afterwards, the method is continued in an eleventh sub-step W11a that corresponds to the seventeenth sub-step G17 shown in fig. 3a. Alternatively, the method is also continued in the eleventh sub-step W11a when it is determined in the tenth substep W10a that the oxygen value is below the lower threshold 3. In this case the combustion mixture is too rich and the data processing device 9 does not wait for the predetermined time and acts immediately.

[0183] If the data processing device 9 determines that the combustion appliance is not commissioned in the nineth step W9a, the method is continued in a twelfth sub-step W12a that corresponds to the eight step G8 shown in fig. 3a.

[0184] After the combustion appliance is ignited in the seventh sub-step W7a, the data processing device 9 can determine whether the flue gas path is blocked in a thirteenth sub-step W13a. This method is explained more in detail in connection with figures 12 to 15 below.

[0185] If the data processing device 9 cannot determine the presence of a flame in the seventh sub-step W7a, the data processing device 9 checks whether a maximum number of ignition attempts are made in a fourteenth sub-step W14a. If this is the case the data processing device aborts the ignition phase and can lock the combustion appliance 1 in a fifteenth sub-step W15a.

[0186] If the maximum number of ignition attempts are not reached, the method the data processing device checks whether the oxygen value fulfills a condition that is dependent on at least one flue gas oxygen value. This is done a sixteenth sub-step W16a and seventieth sub-step W17a. The sixteenth sub-step W16a and the seventieth sub-step W17a are only conducted when they receive data from both the eight sub-step W8a and the fourteenth sub-step W14a.

[0187] In the sixteenth sub-step W16a the data processing device 9 determines whether the measured flue gas oxygen value is within a predetermined range of flue gas oxygen values. The predetermined range of flue gas oxygen values can be between 8% and 20%. In the seventieth sub-step W17a the data processing device determines whether the measured flue gas oxygen value is lower than predetermined value, in particular lower than 2%. If the data processing device determines that the measured flue gas oxygen value is not within the predetermined range of flue gas oxygen values, the method is continued in the sixth sub-step W6a. If it is determined in the sixteenth sub-step W16a that the measured flue gas oxygen values is arranged within the predetermined range of flue gas oxygen values, the data processing device 9 determines in an eighteenth sub-step W18a whether the saved row of the Wobbe table is the last row of the Wobbe table. The data processing device 9 receives the saved row of the Wobbe table in a nineteenth sub-step W19a. The stored value can correspond to the value that is stored in the third sub-step W3a, in a twenty-first sub-step W21a, or in a twenty-fifth sub-step W25a that are described below. If the data processing device determines that the saved row is the last row of the Wobbe table, the method is continued in the sixth sub-step W6a.

[0188] If the data processing device 9 determines in the eighteenth sub-step W18a that the saved row is not the last row in the Wobbe table, the data processing device determines the Wobbe value that is assigned to a row that is at an increased position than the previous row. The row position is increased by 1 so that the next row is adjacent to the previous row of the Wobble table. As discussed above, the Wobbe value decreases with increasing position of the rows in the table. Said Wobbe value and row position is saved in twenty-first sub-step W21a and thus can be later used in the nineteenth step W19a. Additionally, in the twenty-second sub-step W22a the data processing device 9 acts on the throttle unit so that the throttle element is moved to the throttle element position that is assigned to said Wobbe value identified in the twentieth sub-step W20a. Afterwards, the method is continued with the sixth sub-step W6a.

[0189] If the data processing device determines that the measured flue gas oxygen value is not smaller than the predetermined value, in particular 2% in the seventeenth sub-step W17a, the method is continued in the sixth sub-step W6a. If it is determined in the seventeenth sub-step W17a that the measured flue gas oxygen values is smaller than the predetermined value, in particular 2%, the data processing device 9 determines in an twenty-third sub-step W23a whether the saved row of the Wobbe table is the first row of the Wobbe table. The data processing device 9 receives the saved row of the Wobbe table in the nineteenth sub-step W19a. If the data processing device determines that the saved row is the first row of the Wobbe table the method is continued in the sixth substep W6a.

[0190] If the data processing device 9 determines in the eighteenth sub-step W18a that the saved row is not the first row in the Wobbe table, the data processing device determines the Wobbe value that is assigned to a row that is at a decreased position than the previous row. The row position is decreased by 1 so that the next row is adjacent to the previous row of the Wobble table. As discussed above, the Wobbe value increases with decreasing position of the rows in the table. Said Wobbe value and row position is saved in twenty-fifth sub-step W25a and thus can be later used in the nineteenth sub-step W19a. Additionally, in the twenty-sixth sub-step W26a the data processing device 9 acts on the throttle unit so that the throttle element is moved to the throttle element position that is assigned to said Wobbe value identified in the twenty-fourth sub-step W24a. Afterwards, the method is continued with the sixth sub-step W6a.

[0191] The combustion appliances mentioned in the following can executed the methods according to the first embodiment or the second embodiment, which are described in the figures 3-9a.

[0192] Figure 10 shows an overview of a system 10 comprising several combustion appliances, namely a first combustion appliance 1a, a second combustion appliance 1 b, a third combustion appliance 1c and a fourth combustion appliance 1d. In the system 10 shown in figure 10 all combustion appliances 1a, 1 b, 1c, 1d are in an operating mode. The combustion appliances are arranged in a cascade and are connected in parallel to each other.

[0193] The system 10 comprises a fuel gas line 15 by means of which fuel gas can be supplied to the respective combustion appliances 1a, 1 b, 1c, 1d. Additionally, the system 10 comprises a data line 16 by means of which a data exchange can occur between the combustion appliances 1a, 1b, 1c, 1d and / or between the combustion appliances and a master data processing device 14. In the embodiment shown in figure 10 the data processing device of the first combustion appliance 1a corresponds to the master data processing device 14.

[0194] In an alternative embodiment, it is not fixed which of the data processing device of the combustion appliances 1a, 1b, 1c, 1 d acts as the master data processing device, but the master role is taken by one of the data processing devices that are assigned to the combustion appliances 1a, 1 b, 1c, 1d that are in operation mode.

[0195] In the following, the process is explained by referring to the Wobbe value. However, the process also works if the calorific value is used instead of the Wobbe value. Each of the combustion appliances 1a, 1b, 1c, 1d can be configured like the combustion appliance 1 shown in figure 1. The data processing device 9 of the second, third and fourth combustion appliance 1 b, 1c, 1 d transmit the determined Wobbe value to the data processing device of the first combustion appliance 1a that corresponds in this embodiment to a master data processing device 14

[0196] The Wobbe value for an operating combustion appliance 1a, 1 b, 1c, 1 d is determined as follows. The data processing devices 9 assigned to the respective combustion appliances 1 b, 1c, 1d determines the throttle element position of the respective throttle unit 6. Afterwards, the data processing device 9 determines the Wobbe value that is assigned to the throttle element position of the throttle unit 6. Each data processing device 9 can determine the Wobbe value in said manner.

[0197] Additionally, the master data processing device 14 also determines the Wobbe value of the first combustion appliance 1a in said manner and receives the Wobbe values from the remaining data processing devices 9. The master data processing device 14 determines a control Wobbe value that shall be used to control the combustion appliances 1a, 1b, 1c, 1d from the received and determined Wobbe values. Specifically, the master data processing device 14 determines which of the present and received Wobbe values is the latest Wobbe value and / or determines an average Wobbe value on the basis of the received Wobbe values. Said control Wobbe value matches best the current fuel gas quality provided by the fuel gas line 15 to the combustion appliances 1 a, 1 b, 1c, 1d. Afterwards, the master data processing device 14 transmits said determined, latest Wobbe value to all data processing devices 9 of the combustion appliances 1a, 1 b, 1c, 1d. Each of the combustion appliances 1a-1d is controlled dependent on said latest control Wobbe value.

[0198] Specifically, the throttle element position of the throttle unit 6 of each of the combustion appliances 1a-1d is controlled to match to the determined latest control Wobbe value. As discussed above, the throttle element position can be gathered from the Wobbe table that assigns Wobbe values to respective throttle element positions. Specifically, the throttle element position can be determined as each of the combustion appliances 1a, 1 b, 1c, 1d comprises a table in which Wobbe values are assigned to throttle element positions. The Wobbe value or calorific value can be determined according to the method described in fig. 9. Alternatively, the Wobbe value or calorific value can be determined in the fourteenth sub-step N14a shown in figure 8a. The determined Wobbe value or calorific value can be used for information for e.g. an installer. In a cascade situation, the determined Wobbe value or calorific value is not stored in the appliance itself, but can be stored in the cascade controller 35.

[0199] Alternatively, the Wobbe value can be determined only for one of the plurality of combustion appliances and the Wobbe value from said one combustion appliance is used to control all remaining combustion appliances. Alternatively, the Wobbe value can be determined only for one of the plurality of operating combustion appliances and the Wobbe value from said one combustion appliance is used to control all remaining combustion appliances.

[0200] In fig. 10 a cascade controller 35 is provided that is connected with each of the data processing devices 9, 14 of the combustion appliances 1a-1d in a data manner. Thus, the cascade control device 35 and the data processing devices 9, 14 can exchange data. The cascade controller 35 determines which of the combustion appliances is operated and / or determines which of the data processing devices 9, 14 is the master data processing device 14.

[0201] Figure 11 shows an overview of a system 10 comprising several combustion appliances 1a, 1 b, 1c, 1d in a state in which some combustion appliances are non-operating. Specifically, the third combustion appliance 1c and the fourth combustion appliance 1d are non-operating and can be e.g. in a standby mode. For switching the third and fourth combustion appliance 1c, 1d to an operating mode the following steps are necessary. Likewise, to figure 10, the combustion appliances are arranged in a cascade and connected to each other in parallel.

[0202] The master data processing device 14 determines the Wobbe value for the first combustion appliance 1 a and the data processing device 9 determines the Wobbe value for the second combustion appliance 1b. Said determined Wobbe value of the second combustion appliance 1 b is transmitted to the master data processing device 14. The master data processing device 14 and the data processing device 9 can determine the Wobbe value in the same way as it is described for the system shown in figure 10.

[0203] The master data processing device 14 determines which of the received Wobbe values is the latest one. Said Wobbe value is determined as control Wobbe value and transmitted to the second, third and fourth combustion appliance, in particular to the data processing device assigned to the respective combustion appliance 1 b, 1c, 1d. The respective data processing device 9 controls the assigned combustion appliance 1 b, 1c, 1d dependent on the control Wobbe value that is received from the master data processing device 14. Specifically, the throttle element position of the throttle unit 6 is set dependent on the received control Wobbe value. Likewise, the master data processing device 14 can control the first combustion appliance 1a on the basis of the determined control Wobbe value.

[0204] The non-operating combustion appliance 1c, 1d is transitioned from the standby mode to the operation mode as follows. After the data processing device 9 receives a transition signal from the master data processing device 14, the data processing device 9 initializes the ignition phase of the operation mode. Further, the master data processing device 14 sends the determined Wobbe value to the combustion appliance 1c, 1 d to be transitioned to the operation mode. In otherwords, the combustion appliance 1c, 1d to be transitioned positions the throttle element of the throttle unit to the position that corresponds to the Wobbe value sent by the master data processing device 14. This can be done in the third sub-step W3 shown in figure 9 or the fourth sub-step shown in figure 9a.

[0205] Alternatively the non-operating combustion appliance 1c, 1d is transitioned from the standby mode to the operation mode as follows. Said combustion appliance 1c, 1d is selected by the cascade controller 35, which determines the priority of the operation. After the data processing device 9 receives a transition signal from the cascade controller 35, the data processing device 9 initializes the ignition phase of the operation mode. Further, the cascade controller 35 sends the determined Wobbe value to the combustion appliance 1c, 1d to be transitioned to the operation mode. In otherwords, the combustion appliance 1c, 1 d to be transitioned positions the throttle element of the throttle unit to the position that corresponds to the Wobbe value sent by the cascade controller 35. This can be done in the third sub-step W3 shown in figure 9 or the fourth sub-step shown in figure 9a.

[0206] Figure 12 shows a flow chart for detecting blockage in flue gas path of a combustion appliance. This method can be part of the setting of the starting behavior, in particular of the ignition phase, of the combustion appliance 1 that is done in the seventh step G7 or in the sixteenth step G16. Specifically, the blockage detecting can be executed before the starting behavior, in particular of the ignition phase, of the combustion appliance 1 is set. Additionally or alternatively, the blockage detection can be conducted in the thirteenth sub-step W13a shown in fig. 9a. The blockage detection is not limited to the determination whether the flue gas path is fully blocked or not but also determines the blockage level within the flue gas path. In a first sub-step B1 the method for detecting blockage is initiated. As mentioned above this can happen when the ignition phase of the combustion appliance is initiated. In the first sub-step B1 the method for determining the flue resistance level can be selected. The selection can be done manually or according to preset order. The different methods for flue resistance detection are described below in figure 13-15.

[0207] In a second sub-step B2 the parameter that is used for flue resistance determination is measured. In a third sub-step B3 the measured parameter value is converted to a flue resistance value. Specifically, the measured value is converted to a flue resistance level, in particularto a percentage [%] of the flue resistance level. The conversion is made with an empirical relation determined in a lab environment.

[0208] In a fourth sub-step B4 the determined flue resistance level is checked against a predetermined parameter in order to determine the flue resistance status, in particularto determine whether the blockage level of the flue gas path is too high or not. The factor is set by the manufacturer of the combustion appliance or by the installer.

[0209] Figure 13 shows a diagram illustrating how blockage in the flue gas path can be determined according to a first variant. The diagram shows the correlation between the flue resistance level in the flue gas path and a time.

[0210] For determining the blockage in the flue gas path, the time is determined that is needed to reach a predetermined oxygen value. Said oxygen value can be equal or greater than 7,5%. In the example shown in fig. 13, the oxygen value is reached at a time t.

[0211] The diagram shows a predetermined curve 31 that assigns the time to the flue resistance level and thus shows the correlation between the time and the flue resistance level. Said predetermined curve 31 is stored in a memory of the combustion appliance 1. As is it evident from figure 13 an increasing time correlates to an increased flue resistance level.

[0212] In the next step the determined time t is converted to the flue resistance value by using the curve 31 . Thereto, a curve value V1 is determined that is assigned to the time t. The curve value V1 is also assigned to the flue resistance level. Said flue resistance level is checked against a parameter predetermined by the manufacturer or installer to determine whether the flue resistance level in flue gas path is considered to be too high or not. Figure 14 shows a diagram illustrating how blockage in the flue gas path can be determined according to a second variant. The diagram shows the correlation between the flue resistance level in the flue gas path and measured oxygen values.

[0213] In the second variant, the data processing device 9 ensures that the oxygen sensor measures the flue gas oxygen value at a predetermined time-point after the fuel valve 5 is opened. In this case the oxygen value OV was measured at the predetermined time point. For example, the data processing device can ensure that the oxygen value is measured after 2,4 seconds after the fuel valve 5 is opened. As is it evident from figure 14 increasing oxygen values correlate to increasing flue resistance levels.

[0214] The diagram shows a predetermined curve 31 that assigns the oxygen values to the flue resistance level and thus shows the correlation between the oxygen value and the flue resistance level. Said predetermined curve 31 is stored in a memory of the combustion appliance 1. As is it evident from figure 13 an increasing oxygen value correlates to an increased flue resistance level.

[0215] In the next step the measured oxygen value OV is converted to a flue resistance level by using the curve 31. Specifically, a curve value V1 is determined that is assigned to the oxygen value OV. The curve value V1 is also assigned to the flue resistance level. Said flue resistance level is checked against a parameter predetermined by the manufacturer or installer to determine whether the flue resistance level in flue gas path is considered to be too high or not.

[0216] Figure 15 shows a diagram illustrating how blockage in the flue gas path 17 can be determined according to a third variant. The diagram shows the correlation between the flue resistance level in the flue gas path and a gradient of the oxygen value. After the fuel gas valve is opened, the oxygen values are measured.

[0217] The data processing device 9 receives several oxygen values and determines at least one gradient dependent on the received oxygen values. Additionally, the data processing device 9 determines the minimum gradient value MGV during the ignition phase of the combustion appliance 1. The diagram shows a predetermined curve 31 that assigns the gradient values to the flue resistance level and thus shows the correlation between the gradient of the oxygen value and the flue resistance level. Said predetermined curve 31 is stored in a memory of the combustion appliance 1. As is it evident from figure 13 increasing gradient values correlate to an increased load loss.

[0218] In the next step the minimum gradient value MGV is converted to a flue resistance level by using a curve 31 . In fig. 15 the curve value V1 is assigned to the determined minimum gradient MGV. The curve value V1 is also assigned to the flue resistance level. Said flue resistance level is checked against a parameter predetermined by the manufacturer or installer to determine whether the flue resistance level in flue gas path is considered to be too high or not.

[0219] Figure 16 shows a flow chart illustrating how a combustion appliance failure state is determined. In a first sub-step D1 the method is activated. The method can be part of the method by means of which the starting behavior of the combustion appliance 1 is determined and set. That means, the method can be performed in the seventh step G7 shown in fig. 3 when the combustion appliance is in the commissioning mode or in the sixteenth step G16 shown in fig. 3 when the combustion appliance is in the operation mode. In the first sub-step D1 the data processing device 9 receives an oxygen value measured by the oxygen sensor 8.

[0220] In the second sub-step D2 the data processing device 9 determines the combustion appliance state. Specifically, the data processing device 9 determines in the second substep D2 whether the combustion appliance 1 is in a failure state.

[0221] In case that the data processing device 9 determines in the second sub-step D2 that the combustion appliance 1 is in a failure state, the data processing device 9 transmits a failure signal to a display device of the combustion appliance in a third sub-step D3. The failure state of the combustion appliance comprising the failure type is displayed on the display device in the third sub-step D3. Additionally, the data processing device 9 ensures in the third sub-step D3 that the commissioning mode or operating mode of the combustion appliance is stopped. The data processing device 9 then initiates a couple of re-attempts which can ultimately lead to stop the combustion appliance. However, it depends on the failure state whether the data processing device 9 initiates the reattempts. If the data processing device 9 does not determine in the second sub-step D2 that the combustion appliance 1 is in failure state, the starting behavior executed in the seventh step G7 or sixteenth step G16 shown in fig. 3, 3a is continued. Thereto, it is referred to the aforementioned statements referring to the setting of the combustion appliance 1 in the starting behavior.

[0222] Figure 17 shows a diagram showing different states of the combustion appliance 1 during a commissioning mode. The diagram shows a curve 32 of oxygen values that are measured by the oxygen sensor 8 and transmitted to the data processing device 9. Additionally, the diagram shows the time of a start attempt of the combustion appliance 1 . As is evident from fig. 17, the time of a start attempt signal O has a rectangular shape, indicating that the fuel valve 5 is opened.

[0223] Additionally, a lower threshold 24, an upper threshold 23 and a further upper threshold 25 are shown in the diagram. The threshold values relate to oxygen values. Thus, the lower threshold 24 corresponds to an oxygen value that is smaller than the oxygen value corresponding to the upper threshold 23. The oxygen value of the upper threshold 23 is smaller than the oxygen value corresponding to the further upper threshold 25.

[0224] The data processing device 9 determines a combustion appliance state dependent on the oxygen value measured by the oxygen sensor 8. As is explained below more in detail, the data processing device 9 can also consider other combustion parameters for the determination of the combustion appliance state. Dependent on the oxygen value it can be differentiated between the following states.

[0225] If the measured oxygen value is above the further upper threshold 25, the data processing device 9 determines that no fuel, in particular fuel gas, is present and thus determines a combustion failure state, which in the application is also indicated as fourth failure state. The further upper threshold can be 20% of oxygen. Said state is indicated as “State A” in the diagram. Said state is present for example during a time period until the time point t1 in figure 17.

[0226] The data processing device 9 transmits a failure signal to the display device of the combustion appliance stating that no fuel gas is present and / or that the fuel gas supply to the appliance is interrupted. Additionally, the data processing device 9 ensures that the ignition phase of the combustion appliance 1 is aborted and the combustion appliance 1 is switched to blocking or locking mode. A locking mode is the result of a failure state and requires a manual reset of the combustion appliance 1. A blocking mode is the result of a failure state and is a temporary block of the combustion appliance 1 , wherein the combustion appliance 1 will resume an operation mode at a later time, automatically.

[0227] If the measured oxygen value is between the further upper threshold 25 and the upper threshold 23, the data processing device 9 determines that the fuel gas is not sufficiently present and thus determines a combustion appliance failure state, which in the application is also indicated as third failure state. Specifically, the data processing device 9 determines that the air to fuel gas ratio is not correct. Said state is indicated as “State B” in the diagram. To solve the problem, the fuel valve can be adjusted either automatically or manually by the installer. The upper threshold 23 can be 10% of oxygen in the measured gas. State B is present for example in the time period between time point t2 and time point t3 in figure 17.

[0228] The data processing device 9 transmits a failure signal to the display device of the combustion appliance stating that the wrong air to fuel gas ration is detected and thus the air and fuel gas mixture being in the combustion chamber is too lean. Additionally, the failure signal comprises the information to the installer to adjust the fuel valve 5 shown in figure 1. The data processing device 9 ensures that the ignition phase of the combustion appliance 1 is aborted and the combustion appliance 1 is switched to blocking or locking mode or the throttle unit is adjusted such that richer start conditions are achieved during next ignition attempt.

[0229] If the measured oxygen value is between the upper threshold 23 and the lower threshold 24, the data processing device 9 determines that sufficient fuel gas is present or in other words that the measured oxygen value is in the correct range. Said state is indicated as “State C” in the diagram and for example is present in the time period between time point t4 and time point t5 in figure 17. Additionally, the data processing device checks whether the combustion appliancel is ignited. If the combustion appliance is not ignited and thus no flame is detected, the data processing device 9 determines that a combustion appliance component is malfunctioning and thus determines a combustion appliance failure state, which is indicated in the application as second failure state. At this point the data processing device 9 knows that the fan and fuel valve are operating. Most likely the ignition probe, ignition transformer and / or wire harness is malfunctioning. Said information is displayed on the display device of the combustion appliance. The data processing device 9 transmits a failure signal to the display device of the combustion appliance stating that a correct air to fuel gas ratio is detected and that the installer should check for a component malfunctioning or wrong parameter setting. Additionally, the data processing device 9 ensures that the ignition phase of the combustion appliance 1 is aborted and the combustion appliance 1 is switched to blocking or locking mode.

[0230] However, if the data processing device 9 determines that the measured oxygen value is in the correct range and that the combustion appliance is ignited, the data processing device 9 determines that the combustion appliance 1 is in a failure free state so that the ignition phase or operation mode can be continued.

[0231] If the measured oxygen value is below the lower threshold value, for example lower than 2% oxygen, the data processing device 9 determines that the air and fuel gas mixture is too rich to start and thus determines a combustion appliance failure, which in the application is also indicated as first failure state. Said state is indicated as “State D” in the diagram and for example is present in the time period between time point t6 and time point t7 in figure 17. The data processing device 9 displays in the display that components malfunctioning is not expected to be the cause for the failure state. This helps the installer to find the reason for the failure state of the combustion appliance 1.

[0232] The data processing device 9 transmits a failure signal to the display device of the combustion appliance stating that a wrong air to fuel gas ratio is detected and that the detected air and fuel gas mixture is too rich. Additionally, the installer is informed to adjust the fuel valve 5 shown in figure 1 to resolve the combustion appliance failure state. Further, the data processing device 9 ensures that the ignition phase of the combustion appliance 1 is aborted and the combustion appliance 1 is switched to blocking or locking mode. Alternatively, the throttle element position is adjusted such that leaner start conditions can be achieved during the next ignition attempt.

[0233] In the present application “a lean combustion mixture” is a combustion mixture having an air to fuel ratio that is above 1.3. Further, in the application a “rich” combustion mixture is assumed when the air to fuel ratio of the combustion mixture is below 1.2.

[0234] The used time points t1 to t7 are different than the time points discussed below in connection with fig. 18-20. Fig. 18 shows a calibration of the oxygen sensor for a situation in which the oxygen sensor 8 is always heated. The calibration process described below occurs in the fifth step G5 shown in fig. 3, 3a In fig. 18 the time-period in which exists a heat demand, which is known from, e.g., the thermostat settings for central heating, the calibration time interval in which the calibration time is expired, the time-period in which the oxygen sensor is heated and the time-period in which the burner is operated are indicated with black filled rectangles.

[0235] The data processing device 9 initiates a calibration of an oxygen sensor 8 for calibrating the oxygen sensor 8. Thereto, the safety unit control portion 28 of the data processing device 9 transmits a control signal to the sensor data processing unit 20 of the oxygen sensor 8. Additionally, the data processing device 9 initiates a purging of the combustion chamber 18. Thereto, the data processing device 9 transmits a control signal to the fan 5 to run the fan 5 at a predetermined speed for a predetermined time. The data processing device 9 ensures that the calibration initiation and the purging initiation is set such that the oxygen sensor 8 is calibrated during the purging of the combustion chamber 18. The purging initiation can include a pre-purging or post-purging process. Additionally, the data processing device 9 ensures that the burner 7 is stopped during the calibration and / or purging of the combustion chamber 18. As the data processing device 9 knows when a heat request will occur in the intended appliance, such as central heating and / or domestic hot water, the data processing device can determine the time when to initiate pre-purging or post-purging to calibrate the oxygen sensor 8.

[0236] In the situation shown in fig. 18, in which the combustion appliance is powered on, the oxygen sensor 8 is always heated. There exists a heat demand between the first time point t1 and a second time point t2. At said two time points the calibration time interval is not expired. Thus, the burner is operated between the two time points t1 and t2. At the second time point t2 the data processing device 9 initiates purging of the combustion chamber 18. At a third time point t3 the data processing device 9 initiates a calibration of the oxygen sensor 8 that is ended at a fourth time point t4. At the third time point t3 the purging can be finished. Alternatively, the purging can be continued until the fifth time point t5.

[0237] A second heat demand is existent between a fifth time point t5 and an eighth time point t8. The data processing device 9 determines that the time point between the firth time point t5 and a sixth time point t6 corresponds to a burner time point after which the burner is stopped. Specifically, the burner is stopped at the sixth time point t6. The data processing device 9 initiates a post-purging at the sixth time point t6 and a predetermined a calibration of the oxygen sensor 8 likewise as it is explained for the first heat demand. The calibration of the oxygen sensor 8 is ended at a seventh time point t7 and the burner is started again at the seventh time point t7. The burner is operated until an eighth time point t8. Afterwards, the data processing device 9 initiates a further purging and oxygen sensor calibration that is identical to the purging and calibration described before.

[0238] At a ninth time point t9 the calibration time of the oxygen sensor 8 expired. Thus, the data processing device 9 will ensure that the calibration will be done by the next burner start as result of a further heat demand. At a tenth time point t10 the data processing device receives a third heat demand. The data processing device 9 initiates a prepurging of the combustion chamber 18 at the tenth time point t10 which is ended at the eleventh time point t12. At the eleventh time point t11 the data processing device initiates the burner starting so that the combustion appliance 1 outputs heat.

[0239] Fig. 19 shows a calibration of the oxygen sensor for a situation in which the oxygen sensor is not constantly heated. The initiation of the calibration and purging is done in the same way as it is described in fig. 18.

[0240] Likewise, to the situation shown in fig. 18 the heat demands can be prescheduled so that the data processing device 9 knows when there will be a heat demand forthe combustion appliance 1. In the present case there is a first heat demand between a second time point t2 and a third time t3 point and a second heat demand starting at a seventh time point t7. The data processing device can initiate an oxygen sensor heating and a prepurging at a first time point t1 that is before the second time point t2 when the heat demand starts. Specifically, the data processing device can select the first time point t1 that the oxygen sensor 8 is heated up and calibrated such that the calibration ends at the second time point t2. Thus, there is no time loss and the combustion appliance 1 can output heat at the time point t2 without waiting that the oxygen sensor is heated up or calibrated.

[0241] The data processing device 9 initiates a post-purge at a third time point t3 and initiates the oxygen sensor calibration at a fourth time point t4. The oxygen sensor calibration ends at the fifth time point t5. The oxygen sensor can only be calibrated when the oxygen sensor is heated. The data processing device 9 determines that the calibration time is expired at a sixth time point. Thus, the data processing device 9 ensures that the oxygen sensor 8 is calibrated when the next heat demand is received. This is the case for the second heat demand that is received at the seventh time point t7. The data processing device 9 initiates a pre-purge and a calibration of the oxygen sensor 8 at the seventh time point t7. The calibration and the pre-purging are ended at an eighth time point t8 so that the burner starts at the eighth time point t8.

[0242] Fig. 20 shows a calibration of the oxygen sensor for a situation in which the oxygen sensor is heated for a predetermined time. The predetermined time can be 1h. The initiation of the calibration and purging is done in the same way as it is described in fig. 18.

[0243] Likewise, to the situations shown in fig. 18 and 19, the data processing device 9 knows the start time and end time of each heat demand. In this case there is a first heat demand between a second and third time point t2, t3, a second heat demand between a seventh and an eighth time point t7, t8 and a third heat demand between a tenth and eleventh time point t10, t11.

[0244] As the first heat demand starts on the second time point t2, the data processing device initiates to start heating the sensor at a first time point t1. Additionally, the data processing device 9 initiates a pre-purging and calibration of the oxygen sensor 8 at the first time point t1 . The pre-purging and the calibration are ended at the second time point t2 so that the burner starts to combust the air and fuel mixture in the combustion chamber 18. The burner is stopped at the end of the heat demand at the third time point t3. The data processing device initiates at the third time point t3 a post-purging and at a fourth time point t4 a calibration of the oxygen sensor 8. The calibration is ended at a fifth time point t5.

[0245] Likewise, as it is done for the first heat demand, the data processing device 9 initiates to heat up the oxygen sensor 8 and a pre-purging of the combustion appliance at a sixth time point t6, which ends at a seventh time point t7. The burner starts at the seventh time point t7 and ends at an eight time point t8. Further, the data processing device 9 initiates the post-purging and calibration that ends at a nineth time point t9.

[0246] The third heat demand is present at a tenth time point t10. However, at the tenth time point t10 the oxygen sensor is still heated, and the calibration time is not expired. Thus, there is no need for a pre-purging and the burner starts at the tenth time point t10. The burner is stopped at the end of the heat demand, namely at an eleventh time point t11 . The data processing device then initiates a post-purging and a new calibration of the oxygen sensor 8.

[0247] Reference Signs

[0248] 1 Combustion appliance

[0249] 1a First combustion appliance

[0250] 1 b Second combustion appliance

[0251] 1c Third combustion appliance

[0252] 1d Fourth combustion appliance

[0253] 2 Upper threshold referring to operate combustion appliance

[0254] 2a Further upper threshold referring to operate combustion appliance

[0255] 3 Lower threshold referring to operate combustion appliance

[0256] 3a Further lower threshold referring to operate combustion appliance

[0257] 4 Fan

[0258] 5 Fuel valve

[0259] 6 Throttle unit

[0260] 7 Burner

[0261] 8 Oxygen sensor

[0262] 9 Data processing device / control unit

[0263] 10 System

[0264] 11 Fuel gas source

[0265] 12 Heat exchanger

[0266] 13 Manifold

[0267] 14 Master control unit

[0268] 15 Fuel gas line

[0269] 16 Data line

[0270] 17 Exhaust flue path

[0271] 18 combustion chamber

[0272] 19 Sensing element

[0273] 20 Sensor data processing unit

[0274] 21 Throttle element

[0275] 22 Throttle motor

[0276] 23 Upper threshold referring to determining presence of failure state

[0277] 24 Lower threshold referring to determining presence of failure state

[0278] 25 Further upper threshold

[0279] 26 Throttle unit control portion

[0280] 27 Comfort unit portion

[0281] 28 Safety unit control portion

[0282] 29 Temperature sensor

[0283] 31 predetermined curve

[0284] 32 curve related to oxygen values

[0285] 34 heating element

[0286] 35 cascade controller

[0287] A1-A5 Method steps for preparing the combustion appliance to standby mode or to stop

[0288] B1-B4 Method steps for detecting blockage according to the first and second embodiment

[0289] C1-C10, C1a, C4a Method steps in the commissioning mode according to the first and / or second embodiment

[0290] D1-D4 Method steps for determining the combustion appliance state

[0291] G1-G18, G4a Method steps of general operation procedure of the system according to the first and / or second embodiment

[0292] N1-N9, N5a-N13a Method steps in normal operation of combustion appliance according to the first and / or second embodiment 01 First flue gas oxygen value

[0293] 02 Second flue gas oxygen value

[0294] 03 Third flue gas oxygen value

[0295] 04 Fourth flue gas oxygen value

[0296] O Start attempt signal

[0297] P Throttle Position signal

[0298] 51 First operating signal

[0299] 52 Second operating signal

[0300] 53 Third operating signal

[0301] 54 Fourth operating signal t time

[0302] T1-T9 Method steps of testing operation in the commissioning mode t1-t11 time-point

[0303] V1 Determined Value

[0304] W1-W17 Method steps for determining the gas quality according to the first embodiment

[0305] W1 a-W26a Method steps for determining the gas quality according to the second embodiment

[0306] OV Oxygen value

[0307] MGV Maximum gradient value

Claims

PATENT CLAIMS1. Method for operating a, in particular gas adaptive, combustion appliance (1), which comprises an oxygen sensor (8) for measuring an oxygen value in a gas to be measured, and a combustion chamber (18) in which an air and fuel mixture is combusted, wherein the method comprises the following steps: initiating a calibration of an oxygen sensor (8) for calibrating the oxygen sensor (8) and initiating a purging of the combustion chamber (18), wherein the calibration initiation and the purging initiation is set such that the oxygen sensor (8) is calibrated during or after the purging of the combustion chamber (18), wherein the oxygen sensor (8) is electrically heated during the calibration.

2. Method according to claim 1 , characterized in that the purging of the combustion chamber is a post-purging, which is performed after a heat request is ended and / or which is performed when a burner operation is stopped after a burner time-period expired.

3. Method according to claim 1 or 2, characterized in that it is determined during the operation of the combustion appliance (1) whether a calibration time interval during which the oxygen sensor (8) has to be calibrated expired.

4. Method according to claim 3, characterized in that a. a calibration of the oxygen sensor (8) is initialized when a burner operation is stopped because the calibration time interval expired, wherein the calibration is performed during the combustion chamber is post-purged and / or b. a calibration of the oxygen sensor (8) is initialized when the combustion appliance is in a standby-mode and the calibration time interval is expired, wherein the calibration is performed during a pre-purging of the combustion, which is performed before a burner operation starts.

5. Method according to at least one of the claims 1 to 4, characterized in that a calibration of the oxygen sensor (8) is initialized when it is determined that the oxygen sensor is not calibrated when the combustion appliance is started, wherein the calibration is performed during a pre-purging of the combustion chamber.

6. Method according to at least one of the claims 1 to 5, characterized in that a prepurging of the combustion chamber is initiated when the oxygen sensor (8) starts to heat up.

7. Method according to at least one of the claims 1 to 6, characterized in that it is determined whether the heating of the oxygen sensor is started and whether the calibration time interval is expired, wherein a pre-purging of the combustion chamber is initiated when the heating of the oxygen sensor is not started and / or the calibration time interval is expired.

8. Method according to at least one of the claims 1 to 7, characterized in that starting of heating up the oxygen sensor depends on a predetermined time schedule.

9. Data processing device (9, 14) comprising means for carrying out the method of at least one of the claims 1 to 8.

10. Computer program product which, when the program is executed by a computer, in particular a data processing device, cause the computer, in particular the data processing device, to carry out the method of at least one of the claims 1 to 8.

11. Computer readable data carrier having stored thereon the computer program product of claim 10 or data carrier signal carrying the computer program product of claim 10.

12. Combustion appliance (1 , 1a-1d) comprising a fan (4) for controlling an air flow, a fuel valve (5), in particular a fuel gas valve (5), for controlling a fuel flow, a burner (7) for combusting an air and fuel mixture, in particular an air and fuel gas mixture, an oxygen sensor (8) for measuring an oxygen value in a gas to be measured and a data processing device (9) according to claim 9 wherein the data processing device is connected to the fan (4) and fuel valve (5) and oxygen sensor (8).

13. Combustion appliance (1 , 1a-1d) according to claim 12, characterized in that the combustion appliance (1 , 1a-1d) comprises a heating element for electrically heating the oxygen sensor (8).

14. Combustion appliance (1 , 1a-1d) according to claim 12 or 13, characterized in that a. the fuel valve (5), in particular the fuel gas valve (5), is a pneumatic valve, in particular a controllable pneumatic valve, or a stepper valve or a modulator valve and / or in that b. the combustion appliance (1 , 1a-1d) comprises a throttle unit (6) for controlling the fuel flow, wherein the data processing device (9) is connected with the throttle unit (6), in particular a throttle motor (22).

15. Combustion appliance (1) according to at least one of the claims 12 to 14, characterized in that the data processing device (9) is configured to control the throttle unit (6) and / or the fan (4) and / or the fuel valve (5) dependent on the determined at least one oxygen value.

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