hot water supply equipment

Abstract

To provide a hot water supply device capable of suppressing damage to a bypass pipe caused by freezing of water in the bypass pipe without impairing usability for a user. [Solution] For a predetermined time TA after the supply of power from an external power source to the power receiving unit 23 has started, when the hot water supply state is switched from the hot water supply stop state while the setting unit 22E has set the state to be operable, the control unit 22A of the water heater 1 controls the opening degree of the bypass valve 32 to a first opening degree D1 that allows water to pass through the bypass pipe 14, and after the predetermined time TA has elapsed after the supply of power from the external power source to the power receiving unit 23 has started, when the hot water supply state is switched from the hot water supply stop state while the setting unit 22E has set the state to be operable, the control unit 22A controls the opening degree of the bypass valve 32 to a second opening degree D2 that is larger than the first opening degree D1.

Description

[Technical Field]

[0001] The present disclosure relates to a water heater. [Background technology]

[0002] Patent Document 1 describes a hot water supply control device. This hot water supply control device includes a heat exchanger provided between a water inlet and a hot water outlet, and a bypass path that bypasses the heat exchanger between the water inlet and the hot water outlet. A bypass valve is provided in the bypass path, and after hot water dispensing is stopped, the bypass valve throttles the bypass flow rate of the bypass path, preventing cold water from flowing through the bypass path into the hot water outlet path, allowing hot water at an appropriate temperature to be dispensed again. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-288630 Summary of the Invention [Problem to be solved by the invention]

[0004] In a water heater equipped with a bypass passage, it is assumed that the bypass valve will be kept wide open when the operation is stopped (for example, the operation switch is turned off) so that water can be drained from the bypass passage after the operation is stopped. In such a system, when draining water from the water heater to prevent freezing, if the water is drained after the operation is stopped by the operation stop operation (for example, the operation switch is turned off), it will be easier to drain water from the bypass passage without blocking it.

[0005] However, with this type of system, it is up to the user to ensure that the operation is stopped before draining the water, and there is a risk that, for example, the water will be drained without the operation being stopped and the flow of water through the bypass passage being suppressed. If the flow of water through the bypass passage is suppressed during draining, the water will not be drained sufficiently and water will remain in the bypass passage, and depending on the ambient temperature, there is a risk that the remaining water will freeze and cause damage to the bypass passage.

[0006] An object of the present disclosure is to provide a water heater that can suppress damage to a bypass pipe due to freezing of water in the bypass pipe without impairing ease of use for the user. [Means for solving the problem]

[0007] The hot water heater according to the present disclosure includes: A water heater equipped with a gas burner that burns gas to generate combustion exhaust, a water inlet pipe configured as a path through which water flows from the water inlet; A hot water outlet pipe configured as a path for sending hot water to a hot water outlet; a heat exchanger including a heat transfer tube configured as a water passage between the water inlet pipe and the hot water outlet pipe, the heat exchanger transferring heat of the combustion exhaust gas to the water passing through the heat transfer tube; a bypass pipe connected to the water inlet pipe and the hot water outlet pipe and configured as a water passage different from the heat exchanger; a bypass valve configured to be changeable between an open state that allows water to pass through the bypass pipe and a closed state that blocks water from passing through the bypass pipe; an operation unit for performing an operation-on operation and an operation-off operation; a power receiving unit that receives power supplied from an external power source; a setting unit that sets the water heating apparatus to an operable state when the operation-on operation is performed on the operation unit, and sets the water heating apparatus to an inoperable state when the operation-off operation is performed on the operation unit; a control unit that operates based on the power supplied to the power receiving unit and controls the bypass valve; Equipped with At least one of the water inlet path upstream of the connection between the water inlet pipe and the bypass pipe, or the hot water outlet path downstream of the connection between the hot water outlet pipe and the bypass pipe, is provided with a drain plug that can be switched between an open state that allows water to pass through the path and the external space, and a closed state that blocks water from passing through, The control unit During a predetermined time period after the start of power supply from the external power source to the power receiving unit, when the hot water dispensing state is switched from the hot water dispensing state to the hot water stop state while the setting unit is in the operable state, the opening degree of the bypass valve is controlled to a first opening degree that allows water to pass through the bypass pipe; After the predetermined time has elapsed since the start of power supply from the external power source to the power receiving unit, when the hot water dispensing state is switched from the hot water dispensing state to the hot water dispensing stop state in a state where the setting unit has set the operable state, the bypass valve is closed, The first opening degree is an opening degree that allows water to pass through the bypass valve and drain from the bypass pipe when the drain plug is in the open state. Water heater. [Effects of the Invention]

[0008] According to the technology disclosed herein, it is possible to suppress damage to the bypass pipe due to freezing of water in the bypass pipe without impairing usability for the user. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a front view illustrating the appearance of a water heater according to a first embodiment. [Figure 2] FIG. 2 is a schematic circuit diagram conceptually illustrating the internal configuration of the water heater of FIG. [Figure 3] FIG. 3 is a block diagram illustrating a schematic example of the electrical configuration of the controller and the remote controller that constitute the water heater of FIGS. [Figure 4] FIG. 4 is a flowchart illustrating a process for controlling the opening degree of the bypass valve. [Figure 5]FIG. 5 is a timing chart showing changes in the bypass rate in response to changes in the operating state. [Figure 6] FIG. 6 is a graph showing the relationship between the number of input steps of the motor and the bypass ratio. [Figure 7] FIG. 7 is a table showing the relationship between the time from when the pouring of hot water is stopped and the number of correction steps. [Figure 8] FIG. 8 is a graph showing the relationship between the number of input steps of the motor and the bypass ratio. DETAILED DESCRIPTION OF THE INVENTION

[0010] Each of the following [1] to [5] is an example of a water heater included in the present disclosure. [1] A water heater equipped with a gas burner that burns gas to produce combustion exhaust, a water inlet pipe configured as a path through which water flows from the water inlet; A hot water outlet pipe configured as a path for sending hot water to a hot water outlet; a heat exchanger including a heat transfer tube configured as a water passage between the water inlet pipe and the hot water outlet pipe, the heat exchanger transferring heat of the combustion exhaust gas to the water passing through the heat transfer tube; a bypass pipe connected to the water inlet pipe and the hot water outlet pipe and configured as a water passage different from the heat exchanger; a bypass valve configured to be changeable between an open state that allows water to pass through the bypass pipe and a closed state that blocks water from passing through the bypass pipe; an operation unit for performing an operation-on operation and an operation-off operation; a power receiving unit that receives power supplied from an external power source; a setting unit that sets the water heating apparatus to an operable state when the operation-on operation is performed on the operation unit, and sets the water heating apparatus to an inoperable state when the operation-off operation is performed on the operation unit; a control unit that operates based on the power supplied to the power receiving unit and controls the bypass valve; Equipped with At least one of the water inlet path upstream of the connection between the water inlet pipe and the bypass pipe, or the hot water outlet path downstream of the connection between the hot water outlet pipe and the bypass pipe, is provided with a drain plug that can be switched between an open state that allows water to pass through the path and the external space, and a closed state that blocks water from passing through, The control unit During a predetermined time period after the start of power supply from the external power source to the power receiving unit, when the hot water dispensing state is switched from the hot water dispensing state to the hot water stop state while the setting unit is in the operable state, the opening degree of the bypass valve is controlled to a first opening degree that allows water to pass through the bypass pipe; After the predetermined time has elapsed since the start of power supply from the external power source to the power receiving unit, when the hot water dispensing state is switched from the hot water dispensing state to the hot water dispensing stop state in a state where the setting unit has set the operable state, the bypass valve is closed, The first opening degree is an opening degree that allows water to pass through the bypass valve and drain from the bypass pipe when the drain plug is in the open state. Water heater.

[0011] The water heating apparatus described in [1] controls the bypass valve to a first opening degree that allows water to pass through the bypass pipe when the water heater switches from the hot water dispensing state to the hot water dispensing stopped state while the setting unit has set the water heater to an operable state for a predetermined time after the start of power supply from the external power source to the power receiving unit. Thus, the water heater controls the bypass valve to a first opening degree that allows water to pass through the bypass pipe when the water heater switches from the operable state to the hot water dispensing stopped state while the setting unit has set the water heater to an opening degree that allows water to pass through the bypass pipe during a predetermined time after the start of power supply from the external power source to the power receiving unit. Even if the power supply to the power receiving unit is stopped and the bypass valve becomes inoperable in this state, the bypass pipe remains in a state that allows water to pass through, facilitating efficient drainage of water from the bypass pipe. This prevents a situation in which water cannot be drained from the bypass pipe due to the power supply to the power receiving unit being stopped with the bypass valve closed after the hot water dispensing stopped state. This also prevents damage to the bypass pipe due to freezing of water in the bypass pipe, which can occur when water cannot be drained.

[0012] However, if the bypass valve is controlled to the first opening when the hot water supply state is switched from the operational state to the hot water stop state while the system is set to the operational state, water can be drained from the bypass pipe. However, immediately after the hot water is again supplied, a certain amount of cold water will be supplied to the hot water supply pipe through the bypass pipe, which can lead to another problem: hot water at a temperature lower than the set temperature will be dispensed from the hot water outlet. The water heater described in [1] above anticipates this problem and performs a control to set the bypass valve to the first opening when the hot water supply state is switched to the hot water stop state while the system is set to the operational state only within a predetermined time after the start of power supply from the external power source to the power receiving unit. After the predetermined time has elapsed, the bypass valve is controlled to be closed when the hot water supply state is switched to the operational state. This makes the problem of low-temperature hot water less likely to occur after the predetermined time has elapsed. After the predetermined time has elapsed, the water heater is more likely to be used continuously and stably, and it is more likely that the hot water heater will not be recently plugged in or unplugged due to construction work, or left plugged in after a trial run. In other words, since it is expected that there is a low possibility of an incident occurring in which power from an external power source is cut off (for example, power is cut off by unplugging the power outlet), if the device is designed to "control the bypass valve to a closed state when the device is switched to a water supply stop state while set to an operable state" after the above-mentioned specified time has elapsed, it is possible to prioritize user convenience during times when there is a low risk of "the bypass pipe becoming unable to drain due to the power supply to the power receiving unit being stopped while the bypass valve is closed."

[0013] [2] When the operation-off operation is performed on the operation unit, the opening degree of the bypass valve is controlled to a second opening degree that is larger than the first opening degree. The water heater according to [1].

[0014] The water heater of the above [2] controls the bypass valve opening to a second opening degree larger than the first opening degree when the operation is turned off, so that water draining is more easily performed when the water heater is in an inoperable state. On the other hand, when the water heater of the above [2] "is set to an operable state and hot water dispensing is stopped within a predetermined time after the power supply is started," it sets the opening degree to a first opening degree smaller than the second opening degree, so that it can wait in a state where water draining is possible but water flow is suppressed. Therefore, while preparing for unexpected power supply interruptions, it is possible to address to some extent the "problem of low-temperature hot water being easily dispensed."

[0015] [3] If the ratio of the amount of water flowing through the bypass pipe to the amount of water flowing from the water inlet to the hot water outlet is defined as the bypass ratio, the bypass ratio is in the range of 5 to 20% when the bypass valve is set to the first opening degree. The water heater according to [1] or [2].

[0016] In the water heater described above in [3], by setting the bypass ratio to 5% or more, it is possible to ensure the opening of the bypass valve that allows for more reliable water drainage, and by setting the bypass ratio to 20% or less, it is possible to suppress a drop in the temperature of the hot water being discharged the next time it is discharged.

[0017] [4] When the control unit is switched from a hot water discharging state in which hot water is discharged from the hot water discharge pipe to a hot water discharge stop state while the setting unit is in the operable state, for a predetermined time after the start of power supply from the external power source to the power receiving unit, the control unit first increases the opening degree of the bypass valve, then gradually decreases it until it reaches the first opening degree, and after it reaches the first opening degree, maintains it at the first opening degree. The water heater according to any one of [1] to [3].

[0018] The water heater of [4] above increases the opening of the bypass valve once when switching from the hot water dispensing state to the hot water stop state, thereby suppressing after-boiling due to residual heat in the heat exchanger immediately after the hot water dispensing is stopped, and then gradually decreases the opening of the bypass valve to the first opening after the temperature of the heat exchanger has dropped, thereby suppressing damage to the bypass pipe due to freezing of water in the bypass pipe. In other words, it is possible to realize a characteristic control that can achieve both "suppression of after-boiling" and "suppression of damage to the bypass pipe."

[0019] [5] The bypass valve is provided with a stepping motor for changing the opening degree, The control unit adjusts the bypass ratio by controlling the number of steps input to the stepping motor. The water heater according to any one of [1] to [4].

[0020] The hot water supply device of the above [5] can adjust the bypass rate of the bypass pipe with a simple configuration.

[0021] First Embodiment The following description relates to the first embodiment. (Basic configuration) The water heater 1 shown in Figures 1 and 2 is a device that at least performs the operation of supplying water heated by heat exchangers 6, 56 to a bathtub 60, and is configured as a bath and hot water system that has the function of supplying hot water to the bathtub 60 and the function of circulating and heating the water in the bathtub 60. The water heater 1 has an appearance as shown in Figure 1. The water heater 1 has a configuration as shown in Figure 2, and mainly includes a hot water supply side circuit 2 and a bath side circuit 3. As shown in Figures 1 and 2, the water heater 1 has a housing 5, the hot water supply side circuit 2 including the heat exchanger 6, and the bath side circuit 3 having a pipe (drop pipe 70) branching off from the hot water supply side circuit 2. As shown in Figures 1 and 2, the water heater 1 has the hot water supply side circuit 2 and the bath side circuit 3 housed within the housing 5.

[0022] As shown in Figure 2, the hot water supply side circuit 2 includes a hot water supply side water passage, a gas burner 4, a heat exchanger 6, etc. The hot water supply side circuit 2 functions as a circuit that heats tap water supplied from an external source and dispenses hot water. The bath side circuit 3 includes a bath side water passage, a gas burner 54, a heat exchanger 56, a circulation pump 62, thermistors 64 and 65, etc. The bath side circuit 3 is used for circulating and heating water when filling the bathtub, reheating the bath, etc.

[0023] In the hot water supply side circuit 2, a pipe consisting of a water inlet pipe 12, a heat transfer pipe 8a, a pipe 20, a heat transfer pipe 7a, and a hot water outlet pipe 10 functions as the hot water supply side water passage. The water inlet pipe 12 is a flow path (pipe) into which water flows from a water inlet 16. The hot water outlet pipe 10 is a flow path (pipe) that sends hot water to a hot water outlet 18. The gas burner 4 functions as a hot water supply side burner, burning combustion gas to generate combustion exhaust. The heat exchanger 6 functions as a hot water supply side heat exchanger 6. The heat exchanger 6 transfers heat generated by the gas burner 4 to water passing through the hot water supply side water passage (a pipe consisting of the water inlet pipe 12, a heat transfer pipe 8a, a pipe 20, a heat transfer pipe 7a, and a hot water outlet pipe 10) to boil water. The heat exchanger 6 is located midway along the hot water supply side water passage and transfers heat generated by combustion in the gas burner 4 to the water passing through the hot water supply side water passage. The heat exchanger 6 includes a primary heat exchanger 7 and a secondary heat exchanger 8. The primary heat exchanger 7 is disposed in the hot water supply combustion chamber 90 on the upstream side of the combustion exhaust path of the gas burner 4. The secondary heat exchanger 8 is disposed in the hot water supply combustion chamber 90 on the downstream side of the combustion exhaust path.

[0024] In the hot water supply side circuit 2, a water inlet pipe 12 is connected to the inlet of secondary heat exchanger 8 so as to supply tap water. Water inlet pipe 12 is provided with a thermistor 25 that detects the temperature of the water passing through water inlet pipe 12 (specifically, the water temperature at a position in the water supply pipe upstream of heat exchanger 6 and downstream of water inlet 16), and a water volume sensor 34 that serves as a water volume detector that detects the amount of water flowing through water inlet pipe 12 (i.e., the amount of water flowing through the water supply pipe). Thermistor 25 has a function of detecting the temperature of water introduced from outside. When hot water supply to bathtub 60 is stopped (hot water supply solenoid valve 72 is closed), and the stopper (e.g., a faucet) at hot water outlet 18 is closed and the release of hot water from hot water outlet 18 is stopped, no water flows through water inlet pipe 12, and the water flow stops. This is detected by water volume sensor 34. When a stopper (such as a faucet) provided at the hot water outlet 18 is opened and hot water begins to be discharged from the hot water outlet 18, water flows through the water inlet pipe 12 and the hot water outlet pipe 10, and the water flow is detected by the water volume sensor 34.

[0025] The heat transfer pipe 8a of the secondary heat exchanger 8 is connected downstream of the water inlet pipe 12, and further downstream is connected piping 20 that connects the heat transfer pipe 8a of the secondary heat exchanger 8 to the heat transfer pipe 7a of the primary heat exchanger 7. The heat transfer pipe 7a of the primary heat exchanger 7 is connected to this piping 20, and the hot water outlet pipe 10 is connected to the outlet of the primary heat exchanger 7 so that the hot water heated by the primary heat exchanger 7 is discharged. A thermistor 26 that detects the temperature of the water in the hot water outlet pipe 10 is installed in the hot water outlet pipe 10. Of these, the hot water supply side water passage consisting of the water inlet pipe 12, heat transfer pipe 8a, piping 20, heat transfer pipe 7a, and hot water outlet pipe 10 functions as a water passage provided in the hot water supply side circuit 2. Meanwhile, the bath side water passage consisting of the drop pipe 70 and piping 66 functions as a second water pipe provided in the bath side circuit 3.

[0026] The heat exchanger 6 transfers heat generated by the gas burner 4 to water passing through a portion of the hot water supply side water pipe. The heat exchanger 6 functions to recover sensible heat from the combustion exhaust gas using the primary heat exchanger 7 and then recover latent heat using the secondary heat exchanger 8. The primary heat exchanger 7 has a heat transfer tube 7a that serves as a water passage within the primary heat exchanger 7, and transfers the combustion heat contained in the combustion exhaust gas generated by the gas burner 4 to the water passing through the heat transfer tube 7a, thereby transferring the thermal energy of the sensible heat to the passing water. The secondary heat exchanger 8 has a heat transfer tube 8a that serves as a water passage within the secondary heat exchanger 8, and transfers the combustion heat from the combustion exhaust gas generated by the gas burner 4 after it has passed through the primary heat exchanger 7 to the water passing through the heat transfer tube 8a, thereby transferring the thermal energy of the latent heat to the passing water.

[0027] A bypass pipe 14, configured as a water passage bypassing the heat exchanger 6, is provided between the water inlet pipe 12 and the hot water outlet pipe 10. The bypass pipe 14 is provided with a bypass valve 32 that can be switched between a closed state, in which water flow through the bypass pipe 14 is blocked, and an open state, which is more open than the closed state. The bypass valve 32 is equipped with a stepping motor, and the opening of the bypass valve 32 is adjusted in response to a pulse signal input to the stepping motor. Specifically, as the number of steps in the pulse signal increases, the bypass valve 32 moves in a closing direction, and as the number of steps decreases, the bypass valve 32 moves in an opening direction. A water flow control valve 33 is provided in the water inlet pipe 12 upstream of the branch point where the bypass pipe 14 is connected. The water flow control valve 33 is equipped with a motor whose drive shaft rotation angle is controlled by instructions from the controller 22, and is configured to continuously change the opening of the water inlet pipe 12 between a closed state and a fully open state. The water flow rate adjusting valve 33 functions to adjust the amount of water flowing through the water pipe.

[0028] The gas pipe 40 that supplies gas to the gas burners 4 is provided with, from the upstream side, a gas main solenoid valve 42, a hot water gas proportional control valve 44, and hot water switching solenoid valves 46, 46, ... for each branch pipe to each gas burner 4. In addition, a fan 48 that supplies combustion air to each gas burner 4 and gas burner 54 is provided below the hot water combustion chamber 90. A switching solenoid valve 53 is provided in a branch pipe from the gas pipe that is connected to gas burner 54. The hot water gas proportional control valve 44 and hot water switching solenoid valve 46 function to adjust the amount of gas to the gas burner 4.

[0029] In the bath-side circuit 3, the piping 66 includes a piping 67 for guiding water from the bathtub 60 side to the heat exchanger 56 side, a piping 68 for guiding water from the heat exchanger 56 side to the bathtub 60 side, and an intermediate piping 69 connected to the piping 67 and 68 and passing through the heat exchanger 56. The piping 66 has one end and the other end connected to the bathtub 60, and serves as a path through which water leaving the bathtub 60 passes and returns to the bathtub 60. The piping 66 circulates water drawn from the bathtub 60, for example, during reheating or heating operation. The piping 67 guides the water drawn from the bathtub 60 to the heat exchanger 56, and the water that passes through the heat exchanger 56 is then guided back to the bathtub 60 via the piping 68. The gas burner 54 functions as a bath-side burner, combusting combustion gas to generate combustion exhaust. The heat exchanger 56 transfers heat generated by the gas burner 54 to water passing through a portion of the bath-side water pipe (specifically, water passing through the piping 66). The heat exchanger 56 includes a primary heat exchanger 57 and a secondary heat exchanger 58 and functions to transfer heat generated by the gas burner 54 to water passing through a pipe 66 .

[0030] Piping 67 is arranged between bathtub 60 and secondary heat exchanger 58, and is provided with a circulation pump 62 and a thermistor 64 (bath thermistor) that detects the temperature of the water passing through piping 67. The thermistor 64 functions to detect the temperature of the water discharged from bathtub 60 (i.e., the water temperature inside bathtub 60). Circulation pump 62 is a device that moves the water in piping 66, and functions to draw water from the bathtub 60 side and discharge the drawn water toward heat exchanger 56 side.

[0031] Piping 68 is arranged between primary heat exchanger 57 and bathtub 60. A drop pipe 70 branching off from hot water outlet pipe 10 is connected to pipe 67, and hot water supplied from drop pipe 70 flows into pipe 67. Drop pipe 70 is provided with a hot water supply solenoid valve 72 and a drop water volume sensor 74. By opening hot water supply solenoid valve 72 provided on drop pipe 70, hot water heated in hot water supply side circuit 2 can be supplied to bathtub 60. Drop water volume sensor 74 has the function of detecting the amount of water supplied to bathtub 60 via drop pipe 70.

[0032] The drop pipe 70 is a path for passing hot water from the hot water supply side water passage of the hot water supply side circuit 2 to the piping 66 (circulation path) of the bath side circuit 3. The drop pipe 70 branches off from the hot water outlet pipe 10 and communicates with the piping 67, and functions to guide water heated in the heat exchanger 6 through the hot water supply side water passage to the bathtub 60.

[0033] As shown in Fig. 2, water heating apparatus 1 is provided with controller 22. As shown in Fig. 3, controller 22 includes control unit 22A configured as a known microcomputer or the like, memory 22B configured as a known semiconductor memory or the like, communication unit 22C configured as an interface for communicating with the outside, timer 22D capable of measuring the elapsed time since power supply from an external power source started (or since power supply became possible), and setting unit 22E for setting switching between an inoperable state and an operable state. Note that the example of Fig. 3 conceptually illustrates controller 22, and a different configuration from that shown in Fig. 3 may be used as long as it has the same functions as control unit 22A, memory 22B, communication unit 22C, timer 22D, and setting unit 22E.

[0034] The controller 22 is configured to acquire signals from various sensors provided in the hot water supply-side circuit 2 and the bath-side circuit 3 and can control various actuators provided in the hot water supply-side circuit 2 and the bath-side circuit 3. The controller 22 controls the operation of the gas burners 4, 54, the bypass valve 32, and other components. The controller 22 is electrically connected to receive power from a power receiving unit 23. The power receiving unit 23 is a power supply voltage generating unit that enables power supply to the hot water supply device 1 and includes, for example, an outlet plug, a power line, and a power circuit. When an external power source is connected to the power receiving unit 23 and power can be supplied from the outside, power supply is initiated so that a power supply voltage is applied to the control unit 22A. The control unit 22A is electrically connected to the bypass valve 32, the water flow rate adjustment valve 33, the water flow sensor 34, and other components external to the controller 22. The control unit 22A outputs a control signal (pulse signal) to the motor 32A of the bypass valve 32 to change the opening of the bypass valve 32 and adjust the water flow rate through the bypass pipe 14. When the water flow rate detected by water volume sensor 34 exceeds a predetermined value, control unit 22A opens gas main solenoid valve 42, hot water gas proportional control valve 44, hot water switching solenoid valve 46, etc. to start supplying gas to gas burner 4, and also ignites gas burner 4 by causing a spark discharge using an ignition device (not shown), thereby continuing combustion of gas burner 4. Timer 22D sends different measurement signals to control unit 22A during the period from when power from the external power source becomes available to power receiving unit 23 until a predetermined time TA has elapsed, and after the predetermined time TA has elapsed from when power from the external power source becomes available to power receiving unit 23. Setting unit 22E is provided in controller 22, and is a part that switches between an inoperable state (operation off state) and an operable state (operation on state) in response to an operation on remote controller 80.

[0035] As shown in Fig. 3, the multiple remote controllers 80 are arranged in a configuration that allows communication with the controller 22. In the example of Figs. 2 and 3, the multiple remote controllers 80 include a first remote controller 81 provided in the bathroom and a second remote controller 82 provided in a location other than the bathroom (for example, the kitchen).

[0036] As shown in FIG. 3 , the first remote controller 81 includes a control unit 81A configured as a known microcomputer or the like, a display unit 81B configured as a liquid crystal display device or the like, an operation unit 81C provided with a plurality of known switches such as push buttons, an audio output unit 81D including a speaker or the like for outputting audio, and a communication unit 81E for communicating with the controller 22 and the second remote controller 82. The operation unit 81C is configured with a plurality of operation units including an operation switch. In this configuration, the controller 22 switches between an operable state (operation on state) and an operation stopped state (operation off state) for hot water supply operation when the operation switch is pressed. Specifically, when the operation switch is pressed (when the operation on operation operation is performed) while the controller 22 is set to the operation off state (operable state), the controller 22 switches to the operation on state (operable state). When the operation switch is pressed (when the operation off operation operation is performed) while the controller 22 is set to the operation on state (operable state), the controller 22 sets to the operation off state (inoperable state). The inoperable state (operation off state) is a state in which power is supplied to the power receiving unit 23 and in which the controller 22 does not control the ignition of the gas burner 4 and does not supply hot water even when the hot water outlet 18 is open and water is flowing. The operable state (operation on state) is a state in which power is supplied to the power receiving unit 23 and in which the controller 22 ignites the gas burner 4 and supplies hot water when the hot water outlet 18 is open and water is flowing. The other operating units are used for input operations to instruct the filling of the bathtub 60 with water (input operations to instruct automatic filling and input operations to instruct energy-saving filling), input operations to schedule filling, input operations to switch the on / off states of the additional functions described above, and the like.

[0037] The second remote controller 82 is similar and includes a control unit 82A configured as a known microcomputer or the like, a display unit 82B configured as a liquid crystal display device or the like, an operation unit 82C provided with a plurality of known switches such as push buttons, an audio output unit 82D configured as a speaker or the like for outputting audio, and a communication unit 82E for transmitting signals generated by the second remote controller 82 to the controller 22. The second remote controller 82 has the same configuration as the first remote controller 81 or a simplified configuration, and can be set in the same way as the first remote controller 81. The on / off states of both remote controllers 80 are linked. Settings made on one remote controller 80 are reflected in the other remote controller 80.

[0038] (Basic operation) In water heater 1, when the supply of hot water to the bathtub is stopped (hot water solenoid valve 72 is closed), the stopper (such as a faucet) at hot water outlet 18 is closed and the release of hot water from hot water outlet 18 is stopped, no water flows through water inlet pipe 12, and the water flow stops, and water volume sensor 34 detects the water flow stop state. In this state, when the stopper (such as a faucet) at hot water outlet 18 is opened and the release of hot water from hot water outlet 18 begins, or when hot water solenoid valve 72 is opened and the release of hot water into drop pipe 70 begins, water flows through water inlet pipe 12 and hot water outlet pipe 10, and water volume sensor 34 detects the water flow. When the water flow rate detected by water volume sensor 34 exceeds a predetermined value, control unit 22A opens gas main solenoid valve 42, hot water gas proportional control valve 44, hot water switching solenoid valve 46, etc., to start supplying gas to gas burner 4, and also ignites gas burner 4 by generating a spark discharge using an ignition device (not shown), thereby continuing combustion of gas burner 4. If combustion of gas burner 4 continues while a stopper (such as a faucet) provided at hot water outlet 18 is open or while hot water solenoid valve 72 is open, water flows through water inlet pipe 12, heat exchanger 6, and hot water outlet pipe 10, and is heated as it passes through heat exchanger 6, causing hot water to be released from hot water outlet 18 and the bathtub. In this way, the state in which hot water is released outside the hot water heater while gas burner 4 continues to burn when the operation is on (operable state) is the "hot water discharge state."

[0039] On the other hand, in this "hot water dispensing state," if the stopper (such as a faucet) at the hot water outlet 18 and the hot water solenoid valve 72 are both closed and the discharge of hot water from the hot water outlet 18 and into the drop pipe 70 is stopped, water flow stops in the water inlet pipe 12, and the amount of water flow detected by the water flow sensor 34 falls below a predetermined value (water flow stopped state). When the amount of water flow detected by the water flow sensor 34 falls below a predetermined value (water flow stopped state), the control unit 22A closes at least one of the gas main solenoid valve 42, the hot water gas proportional control valve 44, and the hot water switching solenoid valve 46 to cut off the supply of gas to the gas burner 4 and stop combustion of the gas burner 4. In this way, the state in which combustion of the gas burner 4 stops and the supply of hot water to the outside of the hot water heater is stopped in the operation-on state (operable state), which is the "hot water dispensing stopped state."

[0040] (Control of the opening of the bypass valve 32) Fig. 4 is a flowchart showing the processing of the control unit 22A regarding the bypass valve 32. Fig. 5 is a timing chart showing changes in the bypass ratio due to changes in the operating state and the like.

[0041] Control unit 22A starts the processing of Fig. 4 when a state is reached in which power can be supplied from an external power source (for example, a commercial AC power source) to power receiving unit 23 of water heating apparatus 1. For example, when the outlet plug of water heating apparatus 1 is inserted into the external power source or the power supply breaker to water heating apparatus 1 is turned on, switching from a state in which power is not being supplied from the external power source to a state in which power is being supplied to power receiving unit 23, control unit 22A starts the processing of Fig. 4.

[0042] When the control unit 22A starts the processing of FIG. 4, in step S11, the control unit 22A starts measurement by the timer 22D (from the time when the external power source connection is started). After step S11, in step S12, the control unit 22A determines whether the setting unit 22E is set to the above-described operation-on state (operable state). If the control unit 22A determines that the setting unit 22E is set to the operation-off state (inoperable state), the control unit 22A proceeds to the processing of step S18, where the bypass valve 32 is set to the second opening degree. If the bypass valve 32 is already at the second opening degree before performing the processing of step S18, the control unit 22A maintains the bypass valve 32 at the second opening degree in step S18. If the bypass valve 32 is not at the second opening degree before performing the processing of step S18, the control unit 22A changes the bypass valve 32 to the second opening degree and maintains it at the second opening degree in step S18. In this case, the control unit 22A outputs a pulse signal to the bypass motor of the bypass valve 32 to control the bypass valve 32 to the second opening degree D2. The second opening degree D2 is larger than the first opening degree D1, and in this embodiment, the second opening degree D2 is the opening degree at which the bypass valve 32 is most open (the opening degree in the fully open state). Note that the second opening degree D2 is not limited to the fully open state, but may be any opening degree larger than the first opening degree D1. For example, it may be an opening degree slightly closed compared to the fully open state. In this way, when the setting unit 22E is in the above-described operation-off state (inoperable state), the opening degree of the bypass valve 32 is set to the second opening degree D2 regardless of the time measured by the timer 22D.

[0043] If control unit 22A determines in step S12 that setting unit 22E is set to the operation-on state (operable state), it proceeds to step S13, where it determines whether water is flowing through water inlet pipe 12 (i.e., whether combustion is occurring due to water flow in the operation-on state). If control unit 22A determines in step S13 that water flow is not stopped (for example, if it determines that the amount of water flow detected by water flow sensor 34 exceeds a predetermined value), it proceeds to step S17, where it performs control during combustion (control of water flow in the operation-on state). When performing control in step S17, control unit 22A continues control in step S17 if control in step S17 has been performed before, and starts control in step S17 if control in step S17 has not been performed before. While control in combustion (control during water flow) is being performed, control unit 22A controls the aperture of bypass valve 32 using a known method. Specifically, it controls the aperture of bypass valve 32 to an aperture corresponding to the set temperature, inlet water temperature, and hot water output rate.

[0044] If control unit 22A determines in step S13 that water flow is stopped (for example, if it determines that the water flow rate detected by water flow sensor 34 is equal to or less than a predetermined value), control unit 22A proceeds to step S14. Note that the predetermined value for water flow rate can be set to any numerical value, and may be, for example, 0 or a value slightly greater than 0.

[0045] When the process proceeds to step S14, the control unit 22A determines, based on the time measured by the timer 22D, whether a predetermined time TA has elapsed since the power receiving unit 23 became able to receive power from the external power source. The predetermined time TA is the time when it is assumed that the possibility of the power supply from the external power source being cut off becomes low, and can be, for example, the time until the possibility of the power being unplugged becomes low after a trial run after installation. In this embodiment, as an example, the predetermined time TA is set to TA = 10 (hours). The predetermined time TA is not limited to 10 hours and can be set to any other time.

[0046] If control unit 22A determines in step S14 that "a predetermined time TA has elapsed since power receiving unit 23 became able to receive power from an external power source at the time of step S14" (if Yes in step S14), control unit 22A proceeds to step S16. If control unit 22A proceeds to step S16, it closes bypass valve 32 (fully closed state = bypass ratio is approximately 0%). In this case, as shown by the dashed line in FIG. 5, the bypass ratio in the operation-stopped state converges toward 0% over time. Here, bypass ratio BR is defined as the ratio (WB / WM) of bypass flow rate WB, which is the flow rate in bypass pipe 14, to the total water flow rate WM from water inlet 16 to hot water outlet 18.

[0047] If control unit 22A determines in step S14 that "predetermined time TA has not elapsed since power receiving unit 23 became able to receive power from an external power source at the time of step S14," control unit 22A proceeds to step S15 and sets bypass valve 32 to a first opening degree D1. First opening degree D1 is, for example, an opening degree that results in a bypass ratio BR of 12.5%.

[0048] The bypass ratio of the bypass pipe when the bypass valve 32 is fully closed is approximately 0% (i.e., a state in which water flow is blocked), and the bypass ratio when the bypass valve 32 is fully open is approximately 60%. The fully open state opening is the upper limit opening of the bypass valve 32 in the control of Figure 4. When the bypass ratio is 12.5% ​​(when the bypass valve 32 is at the first opening D1), the number of steps of the bypass motor (stepping motor) is 2100 steps.

[0049] Although the bypass ratio when the first opening degree D1 is set to 12.5%, it is not limited to this. For example, it may be greater than 0% and equal to or less than 50%. More preferably, the first opening degree D1 may be set to 5 to 20% of the opening degree in the fully open state.

[0050] After performing the control of steps S15 to S18, control unit 22A returns the process to step S12 and repeats the processes from step S12 onwards. In this way, while hot water is being dispensed, control unit 22A controls the opening degree of bypass valve 32 using a known method depending on the set temperature, inlet water temperature, amount of hot water dispensed, etc., and after hot water dispense is stopped, controls the opening degree of bypass valve 32 depending on the conditions.

[0051] 5 shows a more specific example of control. When the hot water dispensing state is switched to the hot water dispensing stopped state at time T0 while the operation is on (operable state), control unit 22A controls bypass valve 32 to increase the opening degree for a certain period of time (e.g., several seconds) because after-boiling occurs due to the hot water heat in heat exchanger 6 immediately after switching to the hot water dispensing stopped state, and increases the bypass rate for a certain period of time (e.g., several seconds). After temporarily increasing the opening degree of bypass valve 32 in this way, control unit 22A gradually decreases the opening degree of bypass valve 32 over time.

[0052] During the period from when the power receiving unit 23 becomes capable of receiving power from an external power source until a predetermined time TA has elapsed, the control unit 22A temporarily increases the opening of the bypass valve 32 as described above immediately after the hot water discharge is stopped at time T0, and then gradually decreases the opening of the bypass valve 32 until it reaches the first opening D1 (e.g., a bypass rate of approximately 12.5%) at time T1, as shown by the thick line in Figure 5, and after time T1 when the opening of the bypass valve 32 reaches the first opening D1, the control unit 22A maintains the opening at the first opening D1, as shown by the thick line in Figure 5.

[0053] Even after a predetermined time TA has elapsed since power receiving unit 23 becomes capable of receiving power from an external power source, control unit 22A continues to temporarily increase the opening of bypass valve 32 as described above immediately after hot water dispensing is stopped at time T0 from time T0 to time T1, as in the period until the predetermined time TA has elapsed, and then gradually decreases the opening of bypass valve 32. Then, in the control after the predetermined time TA has elapsed, as shown by the dashed line in Figure 5, even after time T1 when bypass valve 32 reaches a first opening D1 (e.g., a bypass ratio of approximately 12.5%), the opening of bypass valve 32 is gradually decreased until it reaches a fully closed state (bypass ratio of approximately 0%), and after the opening of bypass valve 32 reaches the fully closed state, it remains in the fully closed state.

[0054] When the power receiving unit 23 is set to the operation-off state (inoperable state) while receiving power from an external power source, the control unit 22A controls the opening of the bypass valve 32 to the fully open state (bypass rate of approximately 60%). In the example of Fig. 5, the operation-off state is switched to at time T2, and the control unit 22A switches the opening of the bypass valve 32 to the fully open state (bypass rate of approximately 60%) immediately after this time T2.

[0055] The basis for a preferred bypass ratio is explained below. FIG. 6 is a diagram showing the relationship between the number of steps of the bypass motor (stepping motor) that operates the bypass valve 32 and the bypass ratio. The control unit 22A outputs a pulse signal to the bypass motor, thereby changing the bypass ratio (and the opening of the bypass valve 32) according to the number of steps (position). Strictly speaking, because the bypass motor has gear backlash, a positional discrepancy occurs even with the same number of steps when moving from an open position to a closed position and when moving from a closed position to an open position. In the case of 2100 steps, the bypass ratio at 2100 steps when rotated toward the open side is 9.8%, and the bypass ratio at 2100 steps when rotated toward the closed side is 12.6%. Due to these characteristics, the bypass ratio is preferably in the range of 5 to 20%, and when set in terms of the number of steps, a range of 2000 to 2150 steps is preferable. The upper limit of the bypass rate at 2000 steps is 18.7 to 20.9%, and if it exceeds 20.9%, it will have a significant impact on the next hot water outlet temperature, which may result in the standard not being met.On the other hand, the bypass rate at 2150 steps is 4.5 to 7.9%, and if the bypass rate falls below 4.5%, there is a high possibility that water will not be able to be drained.

[0056] Figure 7 is a table showing the relationship between the time from the stop of hot water dispensing and the number of correction steps. The temperature drop in Figure 7 shows a case where the temperature difference between the hot water dispensing thermistor 26 and the inlet water thermistor 25 is within 5°C, and the temperature difference between the inner body outlet thermistor (not shown) located on the outer surface of the hot water supply combustion chamber 90 and the inlet water thermistor 25 is within 5°C. Figure 8 is a graph showing the relationship between the number of steps of the bypass motor and the bypass ratio. As shown in Figures 7 and 8, the number of steps immediately before the stop of hot water dispensing is used as the reference, and after a predetermined time has passed, the bypass valve 32 moves to a position obtained by adding a correction number to the reference number of steps. Specifically, if the number of steps is small, the bypass valve 32 opens, and if the number of steps is large, the bypass valve 32 closes. If the hot water dispensing is stopped while the valve is at position A1 in Figure 8, the valve is controlled to position A3, which subtracts 40 steps. After 20 seconds have passed since the stop of hot water dispensing, the valve is controlled to position A2, which subtracts 20 steps. Within a predetermined time TA (e.g., 10 hours) after power-on, if the position obtained by adding the number of corrected steps from the reference reaches 2100 steps (a bypass rate of 12.5%), the controller 22A restricts the number of steps to not exceed 2100. For example, if 80 seconds or 140 seconds have passed since the hot water supply was stopped, the number of steps would exceed 2100 if the number of steps were set according to the standard. Therefore, the controller 22A does not move to positions C1 to C3 and remains at position B1. On the other hand, after the predetermined time TA (10 hours) after power-on, the controller 22A increases the number of steps until the bypass valve 32 is fully closed (a bypass rate of 0%). Specifically, for example, memory 22B stores a threshold value corresponding to 2100 steps or a bypass rate of 12.5%, and when the threshold value is reached (the number of steps is below the threshold value), the controller 22A maintains the pulse signal at 2100 steps.

[0057] The following description relates to an example of the effect of this configuration. The hot water supply device 1 includes a gas burner 4 that burns gas to generate combustion exhaust, a water inlet pipe 12 configured as a path into which water flows from a water inlet 16, a hot water outlet pipe 10 configured as a path for sending hot water to a hot water outlet 18, heat transfer pipes 7a, 8a configured as a water passage between the water inlet pipe 12 and the hot water outlet pipe 10, a heat exchanger 6 that performs heat exchange so as to transfer heat of the combustion exhaust to the water passing through the heat transfer pipes 7a, 8a, a bypass pipe 14 connected to the water inlet pipe 12 and the hot water outlet pipe 10 and configured as a water passage different from the heat exchanger 6, a bypass valve 32 that is changeable between an open state that allows water to pass through the bypass pipe 14 and a closed state that blocks water from passing through the bypass pipe 14, operation units 81C, 82C that perform an operation on operation and an operation off operation, a power receiving unit 23 that receives power supplied from an external power source, and a control unit 81C that sets the hot water supply device 1 to an operable state when an operation on operation is performed on the operation units 81C, 82C, and and a control unit 22A that operates based on the power supplied to the power receiving unit 23 and controls the bypass valve 32, wherein the control unit 22A controls the opening of the bypass valve 32 to a first opening D1 that allows water to pass through the bypass pipe 14 when the hot water supply state is switched from the hot water supply state set by the setting unit 22E to the hot water supply stopped state while the hot water supply state is set to the operable state by the setting unit 22E for a predetermined time TA after the supply of power from the external power source to the power receiving unit 23 has started, and after the predetermined time TA has elapsed after the supply of power from the external power source to the power receiving unit 23 has started, the control unit 22A controls the opening of the bypass valve 32 to a second opening D2 that is larger than the first opening D1 when the hot water supply state is switched from the hot water supply state to the hot water supply stopped state while the hot water supply state is set to the operable state by the setting unit 22E, and

[0058] Known water heaters 1 have an operation switch that can switch the operation state using an operation switch, such as an operation unit 81C or 82C, provided on a remote controller 80 or the like. When the operation switch is used to shut down the water heater 1, the bypass valve 32 of the bypass pipe 14 is generally opened to its fullest extent to maximize the bypass flow rate. To drain water from the water heater 1 to prevent freezing, the operation switch is turned off to shut down the water heater 1 and then drain the water. In the water heater 1 shown in FIG. 2, a drain plug 28 is provided in the water inlet path upstream of the connection between the water inlet pipe 12 and the bypass pipe 14. The drain plug 28 switches between an open state, which allows water to pass through the path, and a closed state, which blocks water from passing through the path. To drain water from the bypass pipe 14, the drain plug 28 is simply opened. If the bypass valve 32 is open enough to allow water to pass through, the water in the bypass pipe 14 can be drained via the drain plug 28 and released into the outside space. When draining water, in addition to opening drain plug 28, it is also necessary to open another position in the path. The action of opening this other position may be, for example, opening the hot water tap (faucet) that communicates with hot water outlet (hot water outlet) 18, or opening a drain plug at another position on hot water outlet pipe 10 (for example, a position immediately before hot water outlet 18). Alternatively, it may be opening a drain plug provided on a drain pipe that branches off from near piping 20, or, in a configuration in which an automatic drain plug is provided on the path between hot water outlet 18 and the hot water tap, it may be opening this automatic drain plug.

[0059] However, whether or not water is drained while the operation switch is off and the system is not operating is up to the user. If water is drained while bypass pipe 14 is throttled, there is a concern that the water that remains in bypass pipe 14 and does not drain will freeze in winter, causing damage to bypass pipe 14. Particularly in new construction, after a test run is performed after the water heater is installed (with the operation switch on), water is drained (with bypass pipe 14 throttled), and if the power is unplugged or power is cut off by the power breaker in preparation for handover, power will no longer be supplied to the water heater, the anti-freeze heater will not operate, and drainage control according to the outside temperature will not be possible, raising concerns that the water in bypass pipe 14 will freeze and damage the bypass pipe 14.

[0060] On the other hand, as in the case of water heating apparatus 1, by setting bypass valve 32 to first opening degree D1 that allows water to pass for draining for a predetermined time TA after the start of power supply from the external power source to power receiving unit 23, water can be drained from bypass pipe 14, thereby preventing damage to bypass pipe 14 due to freezing of water in bypass pipe 14. For example, after a trial run of water heating apparatus 1 installed before the delivery of a newly built property, the drain plug (e.g., drain plug 28) is opened to drain water, and after the water is drained (in preparation for the delivery of the newly built property), the power supply from the external power source to power receiving unit 23 is cut off (by unplugging the power outlet or by using a breaker) and the freeze prevention heater is not activated, because water has been drained from bypass pipe 14, damage to bypass pipe 14 due to freezing of water in bypass pipe 14 can be prevented. On the other hand, when the bypass valve is set to the first opening degree D1, which allows water to flow through the bypass pipe (not closed), it is possible to drain water from the bypass pipe 14, but the amount of water in the bypass pipe 14 decreases when the hot water is re-discharged, which causes a problem that hot water at a temperature lower than the set temperature is likely to be dispensed from the hot water outlet 18 when the hot water is re-discharged. To address this problem, the bypass valve 32 is set to the first opening degree D1 only within a predetermined time TA (e.g., 10 hours) from when the power supply from the external power source to the power receiving unit 23 is initiated, and after the predetermined time TA has elapsed from when the power supply from the external power source to the power receiving unit 23 is initiated, the bypass valve 32 is fully closed. After the predetermined time TA has elapsed from when the power supply from the external power source to the power receiving unit 23 is initiated, it is unlikely that the power supply from the external power source to the power receiving unit 23 will be cut off (by a power outlet or breaker). Therefore, by closing the bypass valve 32, hot water at a temperature lower than the set temperature is prevented from being dispensed when the hot water is re-discharged, thereby preventing a situation that would impair usability for the user.

[0061] The first opening degree D1 is set so that the amount of water passing through the bypass pipe 14 is in the range of 5 to 20% of the amount of water passing through the bypass valve 32 when it is fully open. By setting the bypass rate to 5% or more, it is possible to ensure an opening degree of the bypass valve 32 that allows water to be reliably drained, and by setting the bypass rate to 20% or less, it is possible to suppress a drop in the temperature of the hot water being discharged the next time it is discharged.

[0062] <Other embodiments> The present disclosure is not limited to the embodiments described above and in the drawings. For example, any combination of features of the above-described or following embodiments is possible within a range that does not contradict. Furthermore, any feature of the above-described or following embodiments may be omitted unless explicitly stated as essential. Furthermore, the above-described embodiment may be modified as follows.

[0063] The first opening degree D1 and the second opening degree D2 are not limited to being configured to converge to a fixed opening degree, but may be configured to vary (without converging) depending on the time elapsed since the hot water supply was stopped and other conditions (temperature, etc.).Furthermore, the bypass ratio BR is not limited to being configured to converge to a fixed bypass ratio, but may be configured to vary (without converging) depending on the time elapsed since the hot water supply was stopped and other conditions (temperature, etc.).

[0064] In the above example, the drain plug 28 is provided in the water inlet path upstream of the connection between the water inlet pipe 12 and the bypass pipe 14, but the drain plug may also be provided in the hot water outlet path downstream of the connection between the hot water outlet pipe 10 and the bypass pipe 14. Even in this case, the drain plug needs to be configured to switch between an open state that allows water to pass through the path and the outside space, and a closed state that blocks water from passing through. Specifically, when the drain plug is in the open state while the bypass valve 32 is open enough to allow water to pass through, the water in the bypass pipe 14 needs to be able to drain from the drain plug via the bypass valve 32.

[0065] It should be noted that the embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is not limited to the embodiments disclosed herein, but is intended to include all modifications within the scope indicated by the claims or the scope equivalent to the claims. [Explanation of symbols]

[0066] 1...Hot water heater 4,54...Gas burner 6,56…Heat exchanger 7a, 8a...Heat transfer tube 10...Hot water outlet pipe 12...Water inlet pipe 14...Bypass pipe 16…Water inlet 18…Hot water outlet 20...Piping 22...Controller 22A...Control unit 22E…Settings section 23...Power receiving unit 28...Drain plug 32...Bypass valve 34...Water volume sensor 81C,82C…Operation unit D1...First opening D2: Second opening BR...Bypass rate TA…Predetermined time

Claims

1. A water heater equipped with a gas burner that burns gas to generate combustion exhaust, a water inlet pipe configured as a path through which water flows from the water inlet; A hot water outlet pipe configured as a path for sending hot water to a hot water outlet; a heat exchanger including a heat transfer tube configured as a water passage between the water inlet pipe and the hot water outlet pipe, the heat exchanger transferring heat of the combustion exhaust gas to the water passing through the heat transfer tube; a bypass pipe connected to the water inlet pipe and the hot water outlet pipe and configured as a water passage different from the heat exchanger; a bypass valve configured to be changeable between an open state that allows water to pass through the bypass pipe and a closed state that blocks water from passing through the bypass pipe; an operation unit for performing an operation-on operation and an operation-off operation; a power receiving unit that receives power supplied from an external power source; a setting unit that sets the water heating apparatus to an operable state when the operation-on operation is performed on the operation unit, and sets the water heating apparatus to an inoperable state when the operation-off operation is performed on the operation unit; a control unit that operates based on the power supplied to the power receiving unit and controls the bypass valve; Equipped with At least one of the water inlet path upstream of the connection between the water inlet pipe and the bypass pipe, or the hot water outlet path downstream of the connection between the hot water outlet pipe and the bypass pipe, is provided with a drain plug that can be switched between an open state that allows water to pass through the path and the external space, and a closed state that blocks water from passing through, The control unit During a predetermined time period after the start of power supply from the external power source to the power receiving unit, when the hot water dispensing state is switched from the hot water dispensing state to the hot water stop state while the setting unit is in the operable state, the opening degree of the bypass valve is controlled to a first opening degree that allows water to pass through the bypass pipe; After the predetermined time has elapsed since the start of power supply from the external power source to the power receiving unit, when the hot water dispensing state is switched from the hot water dispensing state to the hot water dispensing stop state in a state where the setting unit has set the operable state, the bypass valve is closed, The first opening degree is an opening degree that allows water to pass through the bypass valve and be drained from the bypass pipe when the drain plug is in the open state. Water heater.

2. When the operation-off operation is performed on the operation unit, the opening degree of the bypass valve is controlled to a second opening degree that is larger than the first opening degree. The water heater according to claim 1 .

3. When the bypass valve is set to the first opening degree, the bypass ratio is in the range of 5 to 20%, where the ratio of the amount of water passing through the bypass pipe to the amount of water passing from the water inlet to the hot water outlet is defined as the bypass ratio. The water heater according to claim 1 or 2.

4. During the predetermined time period after the start of power supply from the external power source to the power receiving unit, when the state set by the setting unit is switched from a hot water discharging state in which hot water is discharged from the hot water discharge pipe to a hot water discharge stop state, the control unit once increases the opening degree of the bypass valve, then gradually decreases the opening degree until it reaches the first opening degree, and after it reaches the first opening degree, maintains the opening degree at the first opening degree. The water heater according to claim 1 or 2.

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