Thermostat unit

Abstract

A thermostat unit 1 comprises a base unit 3 arranged to be recessed into a surface and enclosing one or more heating relays and control electronics for operating one or more heating systems based on a set temperature and measured temperature. The thermostat unit also comprises a mounting plate 7 securable to the base unit, a first front plate 9 including a plate user interface (45, figure 4), e.g. buttons and touch screen, to forward user input to the control electronics, and a second, decorative front plate. The first front plate and second front plate are releasably securable to the mounting plate so that one of the first and second front plate is fitted to the mounting plate on installation. Ideally the base unit includes means to enable wireless communication with one or more wireless devices (e.g. mobile phones) other than the first front plate, each device having a device user interface (e.g. mobile phone application) to forward user input to the control electronics. The base unit ideally comprises a cuboidal housing 11, separator plate 11c and front face 13. The thermostat unit may also comprise a mounting plate 5. A kit of parts is also claimed.

Description

The present invention relates to a thermostat unit having a front plate that is removable or interchangeable. It is commonly known for electric heating systems to have wall mounted thermostats for a user to set a desired temperature in a particular area, and to set and adjust heating programs and schedules. The thermostat is typically situated in a location that is convenient for users and that measures a representative temperature of the area heated by the system. The thermostat is often located remotely from the parts of the heating system that are operated to change the temperature (such as underfloor heating elements, towel rail elements, electric radiators, boilers (gas and electric), immersion heaters and central heating / hot water valves) and communicates control signals either wired or wirelessly. Typically, wall mounted thermostats have an enclosure containing the control electronics projecting out of the wall the thermostat is mounted on. The control electronics include switch relays that control the heating devices. The switch relays communicate directly to the controller of the heating device(s). In some cases, the enclosure may be removable. In this case, the switch relays are located in a base unit mounted on or within the wall, and the control electronics in the enclosure communicates wirelessly with the switch relays. Wall mounted thermostats are bulky. Furthermore, even where the enclosure is removable, the base units are still required as they house at least part of the control electronics necessary for controlling operation of the heating system. The base unit still projects out from the wall in an undesirable manner. According to a first aspect of the invention, there is provided a thermostat unit comprising: a base unit arranged to be recessed into a surface, the base unit enclosing one or more heating relays and control electronics for operating one or more heating systems based on a set temperature and a measured temperature; a mounting plate securable to the base unit; a first front plate comprising a user interface arranged to forward user input to the control electronics; and a second front plate comprising a decorative front plate, wherein the first front plate and second front plate are releasably securable to the mounting plate, such that one of the first front plate and the second front plate is fitted to the mounting plate on installation. The base unit may comprise wireless communications means for communicating with one or more wireless devices, different to the first front plate, each comprising a user interface to forward user input to the control electronics. At least one user interface may be provided by a mobile phone application. Only the user interface provided by the one or more wireless devices may be used to operate the one or more heating systems when the second front plate is used to assemble the thermostat unit. The user interface in the first front plate may only be operational when the first front plate is fitted on the mounting plate and base unit. The user interface may only receive user commands and forward them to the control electronics in the base unit and receive status information from the control electronics in the base unit for display. The user interface in the first front plate may be in communication with the control electronics by a short range wireless connection. The user interface in the first front plate may be in communication with the control electronics by a physical connection through the mounting plate. The thermostat unit may comprise a cover plate, securable to a rear of the first front plate, to enclose the electronics of the user interface. The mounting plate may be securable to the base unit by interengaging projections or clips. The interengaging projections or clips may be positioned at a peripheral edge of the base unit. The interengaging projections or clips may be rotationally asymmetric around the base unit, to control the relative orientation between the base unit and the mounting plate. The mounting plate may be securable to the wall through one or more screw holes, arranged outside the interengaging projections. The front plate may be securable to the mounting plate by a captive screw. The base unit may enclose a plurality of relays, each relay having a relay input associated with a temperature sensor, and a relay output associated with one or more heating devices. Each temperature sensor may be selectively coupled to any one of the relays. The or each heating relay may be disconnectable from the temperature sensor, such that the thermostat acts as a timer switch. The relays may be able to control one or more of the following: underfloor heating elements, towel rail elements, radiators, electric boilers, gas boilers, immersion heaters and central heating / hot water valves. The relays may be able to control one or more zones of a heating system, with a separate relay and temperature sensor for each zone. According to a second aspect of the invention, there is provided a kit comprising: a base unit enclosing one or more heating relays and control electronics for operating one or more heating systems based on a set temperature and a measured temperature; a mounting plate securable to the base unit; a first front plate comprising a first user interface arranged to forward user input to the control electronics for operation of the one or more heating systems; and a second front plate comprising a decorative plate, wherein the first front plate and second front plate are releasably securable to the mounting plate; wherein when first user interface is only operational when the first front plate is secured to the mounting plate; and wherein when the second front plate is secured to the mounting plate, a second user interface is provided, through a wireless device in communication with the control electronics. The inventors have realised that for a thermostat with a fixed front plate, putting the control electronics in a base unit, which is recessed into the wall, means the front plate can be made slimline. Furthermore, where a user wishes to control the heating without a wall mounted display, for example using an app on their phone or a building management system, a simple decorative blanking plate can be provided. The same basic module can be used to provide both the functional thermostat and blanking plate, just by changing the front plate. The base unit may be positioned at a low level, where an electrical fused spur would normally be located. Where the front plate does provide a user interface, the front plate simply acts as a conduit for communications between the base unit and user interface. All communications are conveyed from the user interface, to the base unit, to the heating devices. Similarly, when the decorative blanking plate is used, a remote device, such as a mobile phone application, can provide the same function. The front plate with the user interface does not allow for remote operation - it only works when it is connected to the base unit. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 illustrates a wall mountable thermostat unit according to one embodiment, in exploded view; Figure 2A illustrates the housing of the base unit from the wall mountable thermostat unit of Figure 1; Figure 2B illustrates the front face of the base unit; Figure 2C illustrates the assembled base unit from the wall mountable thermostat unit of Figure 1; Figure 3 illustrates the mounting plate from the wall mountable thermostat unit of Figure 1; Figure 4 illustrates the front plate of the wall mountable thermostat unit of Figure 1; Figure 5 illustrates the rear cover of the front plate of the wall mountable thermostat unit of Figure 1; and Figure 6 schematically illustrates a heating system operated using the thermostat unit of Figure 1. Figures 1 to 5 illustrate a thermostat unit 1 that can be mounted on a wall (not shown) to control the output of a heating system 100 (discussed with reference to Figure 6). As will be appreciated, the thermostat unit 1 may control the heating system 100 by receiving a set temperature input by a user or a heating program, comparing this to a measured current temperature, and controlling the heat output accordingly. The thermostat unit 1 illustrated in Figure 1 includes, in a forward direction, a base unit 3, a mounting plate 5, a rear cover 7 and a front plate 9. The base unit 3, mounting plate 5, rear cover 7 and front plate 9 are assembled to provide a wall mounted thermostat 1. The front plate 9 provides the forward facing face of the thermostat, seen by the user during use. The base unit 3 is shown in Figures 2A to 2C in more detail. As shown in Figure 2A, the base unit 3 comprises a substantially cuboidal housing 11 defining a three-dimensional volume for enclosing the control electronics of an electric heating system. The base unit 3 has a rear wall Ila, and a sidewall 11b extending forward from the rear face Ila. The front of the cuboidal housing 11 is open. The housing 11 may be of similar size to a pattress box or other common electrical enclosures, so that it is of standard size. As will be discussed below in more detail, the housing 11 of the base unit 3 encloses heating relays, which are coupled to the heating devices, temperature sensors (it may be that only connectors for the temperature sensors are provided), control electronics for operation of the heating system and may also enclose control components for providing a user interface. In some embodiments, the housing 11 of the base unit 3 also encloses communication means for communicating with a user interface, the temperature sensors, and other parts of the heating system 100 controlled by the thermostat unit 1. This may be by wireless communications and / or wired communications (for example connectors may be provided for wired communications). Furthermore, the base unit 3 may also enclose the hardware to provide networking devices for remote control of the thermostat via a smart phone app, internet portal or other means such as a building management system. The base unit 3 is also provided with a separator plate 11c, shown in Figure 1. The separator plate 11c is provided within the volume defined by the housing 11. The separator plate 11c divides the volume into two separate portions, a first portion enclosing the high voltage components and a second portion enclosing the low voltage components. In the example shown, the separator plate 11c is planar, extending parallel to the rear wall Ila. However, it will be appreciated that any shape and orientation of separator plate 11c may be used. In the example shown, the interior of the sidewall 11b is provided with formations or clips 67 to act as a stop and locate the separator plate 11c. The rear wall Ila and sidewall 11b may be formed with slots 59a and / or fins 59b to assist removal of heat from the electronics in the volume. Figure 2B shows the front face 13 of the base unit 3. The front face 13 of the base unit 3 is formed separately from the housing 11. This allows the electrical components and separator plate 11c to be inserted during manufacture. After the contents are provided in the volume, the front face 13 is fixed to the housing 11. The front face 13 also includes an aperture 19 for passing a physical connection to the electrical components in front of the base unit 3 (such as sensors or elements for user input or output) is required. Optionally, the aperture 19 in the front face may be aligned with the aperture 69 in the separator plate 11c, but this is by way of example only. As best shown in Figure 2A, the forward-facing edge 61 of the sidewall 11b of the housing 11 includes a number of notches 63 extending a short distance backwards toward the rear wall 1 la of the housing. The front face 13 of the base unit 3 is sized to snugly fit within the periphery defined by the forward facing edge 61 of the housing 11. As best shown in Figure 2B, the front face 13 includes a number of tabs 65 extending from the sides of the front face 13, in the same plane as the front face 13. In the assembled base unit 3, as shown in Figure 2C, the tabs 65 sit in the notches 63 formed in the housing 11. The depth of the notches 63 and the thickness of the tabs 65 is such that the front face 13 sits flush with the forward-facing edge 61 of the sidewall 11b. The notches 63 and tabs 65 are arranged around the side wall 11b and front face 13 such that the front face 13 only fits into the housing 11 in a single arrangement. In the example shown, two engaging notches 63 and tabs 65 are provided on the top of the housing 11 and one is provided on the bottom, with none on the sides. However, it will be appreciated that any arrangement of the tabs and notches that has no rotational symmetry may be used. Alternatively, the front face 13 and shape of the sidewall 11b may be arranged to provide the location of the front face in the correct orientation. It will be appreciated that the separator plate 11c may also be arranged to ensure it can only be installed in the volume in one orientation, in a similar manner to the front face 13. The front face 13 and separator plate 11c may be secured to the housing 11 by clip fit projections, hooking projections, screws, or any other suitable means. The mounting plate 5 is shown in more detail in Figure 3. The mounting plate 5 is formed by a substantially square planar body 17. In the assembled thermostat unit 1, the mounting plate 5 extends parallel to the rear wall Ila and the front face 13 of the base unit 3. The body is larger than the front face 13 of the base unit 3, such that the mounting plate 3 provides a border around the base unit 3, when viewed from the front. The mounting plate 5 has a back face (not shown) facing towards the base unit 3 and a front face 27 facing forward, and towards the front plate 9. A central aperture 21 is formed extending through the thickness of the mounting plate 5. The central aperture 21 is substantial square, and positioned in the centre of the mounting plate 5. The aperture 21 is approximately the same size as the front face 13 of the base unit 3. On each side of the four sides of the aperture 21, away from the corners, tabs 39, 40, 41, 42 are formed extending partially over the opening. In the assembled thermostat unit 1, the tabs 39, 40, 41, 41 locate the mounting plate 5 relative to the base unit 3 in the direction extending from the back to the front of the thermostat unit 1. The tabs 39, 40, 41, 42 engage the front face 13 of the base unit preventing the mounting plate 3 moving further backwards. On the rear face of the mounting plate 5, sprung projections 23, 25 are formed extending backwards, at the edge of the central aperture 21. Two projections 23, 25 are shown in Figure 3, however, it will be appreciated that projections may be provided adjacent each edge of the aperture. The sprung projections 23, 25 have enlarged heads 29. The sprung projections 23, 25 engage with corresponding recesses 31, 33, 35, 37 formed in the outer surface 15 of the side wall 1 lb of the base unit 3. The outer surface 15 faces perpendicular to the rear Ila and front 13 faces of the base unit 3, and outward from the volume defined by the housing 11. The sprung projections 23, 25 and recesses 31, 33, 35, 37 are arranged as click fit or interengaging projections arranged to secure the mounting plate 5 to the base unit 3. The recesses have a first portion 31a, 37a extending backwards from the forward-facing edge 61 of the housing 11, and a second portion 31b, 37b, for receiving the enlarged head, the first portion 31a, 37a is separated from the second portion 31b, 37b be a dividing wall 31c, 37c. The side of the dividing wall 31c, 37c facing forward is sloped towards the first portion of the recess 31. The spring force of the projections 23, 25 acts to push the enlarged head 29 inwards. When the mounting plate 5 is fitted to the base unit 3, it is pushed backwards onto the front of the base unit 3. The projections 23, 25 align with the corresponding recesses 31, 33, 34, 36 and the sloped side of the dividing wall 31c, 37c acts against the urging force, so the enlarged heads deflect outwards to move past the dividing wall 31c 37c. The shape of the dividing wall prevents similar deflection of the projections 23, 25 when they are pulled forwards, after being installed. The projections 23, 25 may be sprung by being formed of a resiliently deformable material, in a similar manner to snap fit projections, or may be sprung in any other way. The projections 23, 25 may be arranged rotationally asymmetrically around the aperture, to ensure that the mounting plate 5 may be fitted to the base unit 3 in one orientation only. A pair of screw holes 42a, 42b are also provided extending through the mounting plate 5. The screw holes are used for securing the mounting plate 5 (and hence the base unit, which is fixed to the mounting plate 5) to the wall. As such, the screw holes 42a, 42b are provided in the portion of the mounting plate 5 that forms the border outside the area of the base unit 3. Figure 4 shows the front plate 9 in more detail. The front plate 9 is substantially square when viewed front on and has a front face 43 defining input and output elements 47 for forming a user interface 45. In the example shown, the input and output element 47 may comprise point light emitting elements (such as light emitting diodes) arranged to form an alpha-numerical display, and buttons for operation of the system. However, it will be appreciated that any suitable arrangement of input and output elements may be provided, such as mechanical switches or buttons, touch screens, or any other kind of element. The front plate 9 includes sidewalls 49 extending backwards from the front face 43 around the edge 51 of the front face 43. This defines a volume (not shown) on the rear of the front plate 9 which houses the electronics necessary for operating the user interface 45 and forwarding instructions to the base unit 3, as will be discussed in more detail below. The volume at the rear of the front plate 9 is open facing backwards. The rear cover 7, shown in Figure 5, is provided to close this volume. This encloses and protects the contents of the volume before the front plate 9 of the thermostat unit 1 is assembled. The front plate 9 and rear cover 7 are arranged so that when assembled as a single unit, the rear cover 7 sits within the volume defined by the front plate 9. Therefore, the sidewalls 49 extend further backwards than the rear cover 7. and the sidewalls 49 of the front plate 9 extend around the edge 30 of the mounting plate 5. Returning to Figure 3, the mounting plate 5 includes a projection 53 on its lower edge, with a vertically extending screw hole 57. The rear cover 7 of the front plate 9 includes a cut-out section 71 aligned with the projection to allow the rear cover 7 to fit over the projection 53. The lower sidewall 49 of the front face includes a hole (not shown) aligned with the screw hole 57 in the projection. The front face 9 is secured to the mounting plate by a captive screw (or other type of screw) secured through the sidewall 49 of the front face and the screw hole 57 in the projection. Whilst the front cover 9 can be removed from the mounting plate 5 and base unit 3 during installation or maintenance, it is not removable during general operation by a user. The rear cover 7 is provided with an aperture 55, that aligns with the apertures 19, 21 in the base unit 3 and mounting plate 5 when the thermostat 1 is assembled, to allow passage of a physical connection from the electrical component in the base unit 3 to components in the volume of the front plate 9. The rear cover 7 is secured to the front plate 9 by any suitable means. For example, the front plate 9 may include retaining projections (not shown), which the rear cover 9 can be slide between to clip into place. Alternatively, clips, click fit projections, screws or other connection means can be used. Optionally, the sidewalls 49 may be provided with cooling holes 57 arranged around part or all of the sidewalls 49 to allow airflow into the enclosed volume formed by the front face 43, sidewalls 49 and rear cover 9. These cooling holes 57 may be omitted. The base unit 3 and the front plate 9 and rear cover 7 are assembled as separate units during manufacture of the thermostat unit. In use, when the thermostat unit 1 is to be provided on a wall, an installer first fixes the mounting plate 5 to the base unit 3 using the clips discussed above. The base unit is then placed in a recess formed in the wall, with the mounting plate 5 extending over the surface of the wall. Screws are then provided to fix the mounting plate 5 to the wall. The front module, including the rear cover 7 and front plate 9 is then secured to the mounting plate 5 using the captive screw discussed above. As discussed above, the contents of the base unit 3 are connected to the front plate 9 by a physical wired connection (not shown) passing through the apertures 19, 21, 55 in the base unit 3, mounting plate 5 and rear cover 7. In some examples, this may be wires or cables extending through the apertures 19, 35, 55. In other examples plug connectors may be provided in one or both of the base unit 3 and rear cover 7 in the apertures 19, 55. The plug connectors may connect through the mounting plate 5, either directly, by an intermediate cable, or by a connector formed in the mounting plate 5. Figure 6 schematically illustrates a heating system 100 operated from the thermostat 1 discussed above. As shown in Figure 6, the heating system 100 includes a number of heating devices such as a boiler 102a, an underfloor heating system 102b and an immersion heater 102c. In the example shown, each heating device 102a-c is controlled by a corresponding relay 106a, 106b, 106c enclosed in the base unit 3 of the wall mounted thermostat 1. The relays 106a-c are connected to the heating devices 102a-c through dedicated physical connections which may be wired. Alternatively, each heating device may have a corresponding relay and transceiver, in which case the connection may be wireless. The base unit 3 also encloses a communication interface 108 for communication with the user interface in the front plate 9, temperature sensors 104a-c for controlling operation of the heating devices 102a-c and any other parts of the heating system and other systems as required. In some examples, the communications interface 108 may also control communications between the relays 106a-c and heating devices 102a-c. In other examples, the relays 106a-c may have a dedicated communications interface or transceiver. The communications interface 108 may be capable of performing communications using one or more different protocols, and communications may be wired or wireless. For wireless communications, the communications interface 108 may include one or more different wireless transceivers. Any suitable wireless communication method may be used for wireless communications in the heating system. For example, the wireless connections may be by Bluetooth, WiFi, thread, zigbee, 3G, 4G, 5G, over the internet, IR or any other short or long range transmission methodology. The base unit 3 further encloses a memory 110 that contains a program storage portion 112 which includes computer program instructions 112a for operation of the relays 106a-c, to control the output of the heating devices 102a-c. In order to control operation of the relays 106a-c, a temperature in the vicinity of the heating devices 102a-c is measured by the corresponding temperature sensors 104a-c. The temperature sensors 104a-c send temperature data to base unit 3 via the communications interface 108. A target temperature for the area heated by each heating device 102a-c is set by a user through the user interface 45 in the front plate 9. It will be appreciated that when referring to a water heating device, such as an immersion heater 102c, the temperature in the area heated by the device 102c may be the water temperature. In the example discussed above, the output part of the user interface comprises point LEDs and the input part comprises touch sensitive push buttons. Drivers for controlling operation of the LEDs, and for controlling input through the push buttons are provided. Part or all of the drivers for the user interface may be provided in the base unit 3. In this case, the enclosed volume in the front plate may simply enclose the printed circuit board (PCB) or other support structure for providing the user interface elements 47 and a communications interface / connector 116 may simply forward signals to / from the front plate 9 to the base unit 3. In some cases, the enclosed volume of front plate 9 may include some or all of the processing circuitry 118 to implement the user interface 45. However, it will be appreciated that at most, the enclosed volume in the front plate 9 only encloses circuitry related to the user interface 45, and no circuitry related to operation of the heating system. Optionally, a temperature sensor 104a-c may be provided in the front plate 9. Drivers for the temperature sensor may also be provided in the base unit 3 or in the enclosed volume of the front plate 9. A memory 114 may also optionally be provided in the front plate 9 to store any data required to implement the user interface 45 and to act as a buffer in case the set temperature is not able to be transmitted immediately. In some examples, the memory 114 and / or processing circuitry 118 may be omitted from the front plate 9 and the user interface may be controlled from the base unit 3 only. The relays 106a-c, provided within the base unit 3, may include processing means that use the set temperature and measured temperature to control the heating output of each heating device 102a-c to ensure the measured temperature reaches the set temperature and maintains the set temperature. Alternatively, the control of the relays may be provided by a separate processing means 120 enclosed in the base unit 3. Within the base unit, a signal bus 122 is provided to connect the relays 106a-c, memory 110, communications interface 108 and processing means 120. Similarly, within the front plate 9 a signal bus 124 is provided to interconnect the user interface 4,5 communications interface / connector 116 and, if present the memory 114 and processing means 118 (including drivers for output LEDs and input buttons and any temperature sensors). It will be appreciated that some or all of the components in the base unit 3 and / or the front plate 9 may be mounted on printed circuit board (not shown) such that the bus 122, 124 is provided by conducting tracks on the board, or connected in any other means. In the above example, communication from the front plate 9 to the base unit 3 is by physical wired communications, and the front plate 9 should be connected to the base unit 3 to control the heating system. The front plate 9 includes no independent power source, and so the user interface 45 in the front plate 9 is only operational when connected to the base unit 3. In another example, communication from the front plate 9 to the base unit 3 may be by a short-range wireless communication method. It may be that power is still provided to the front plate 9 by a wired connection (or by wireless power transfer) in which case the user interface in the front plate 9 is still only operational when fitted to (or in very close proximity to) the base unit 3. If the front plate 9 uses wireless communications and does not have a wired power connection, a power source such as battery 126 may be used to power the components in the front plate 9. Since the front plate 9 is only a user interface that relays / forwards instructions and provides information to the user, the components are relatively low powered. The battery 126 may be removable and replaceable. Alternatively, the battery may be chargeable. As discussed above, the base unit 3, mounting plate 5 and rear cover 7 have apertures 19, 35, 55. These apertures 19, 35, 55 may be used to provide a power connection for charging the battery 126, and also optionally for powering the front plate 9 when it is clipped in place. Alternatively, wireless power transfer may be used to charge the battery 126. When the front plate 9 uses wireless communications and does not have a wired power connection, the apertures 19, 35 55 for cable connections may optionally be omitted. In embodiments with wired connections to the front plate 9, the front plate 9 may still include a battery 126 as a backup power source, or this may be omitted. The control relays 106a-c and heating devices 102a-c may also be controlled through user interfaces 45 provided on external devices 128a, 128b. This may be, for example, a software application (app) or private website on a mobile phone, a computer, a tablet and the like. It may be that input through the interface 45 on the front plate 9 (or another device 128a,b determined by the user) is able to override other inputs. The control system housed within the base unit 3 may be powered by a mains power connection provided through plugs or other connections in the sides or rear of the base unit 3. Similar means may be used to connect sensors and heating device if wireless communications is not used. A battery may be provided, for example for backup in the event of power disruption. When the front plate 9 is fitted, the user interface 45 on the front plate is operational for control of the heating system. The user interfaces 45 provided through the external devices 128a, 128b may also provide operational user interfaces 45. In some examples, a user may choose that they do not want to use a wall mounted thermostat. For example, they may only wish to use their mobile phone 128a (or other external device) to provide input and output. The heating relays 106a-c are still required to be located somewhere suitable for installation such as in a wall or floor space, and access is still required to these for maintenance and repair. In this case, the front plate 9 (and rear cover 7) may be replaced by an alternative front plate that simple provides a decorative covering. The decorative covering plate connects to the mounting plate 7 in the same way as the front plate 9 with a user interface 45, using a captive screw through the projection 53. In this case, the user interface 45 provided in the front plate 9 is not operational. This may be because there is no power (or data commands) provided by physical connection, or the front plate is out of range for short range wireless communications and / or wireless power transfer. It will be appreciated that the thermostat 1 may be provided as a kit, including the base unit 3, mounting plate 5, a front plate 9 (with rear cover 7) and a decorative front plate. The installer may then select one of the front plate 9 and decorative plate to use in installation since the two are interchangeable, and the heating system 100 can operate without the need for the components in the front plate 9. This is because the front plate 9 merely forwards inputs and outputs and acts as a user interface - all the control electronics for operating the heating system 100 is in the base unit 3. Where the front plate 9 is used, communication of user inputs is relayed to the base unit 3, and then on to where it is actioned in the heating system 100, and data output is provided to the user from the base unit 3. The base unit 3, mounting plate 5, rear cover 7. front plate 9 and decorative plate may be made of any suitable material. For example, they may be any rigid plastic, metal or the like. In some examples, the base unit 3 is sized to fit within a standard sized electrical base unit, or to be the same size as a standard sized electrical base unit. However, in other examples, the base unit may be any suitable size. In the example discussed above, the base unit 3 has a closed front 13, which is formed separately. This may be by way of example, the front 13 may not be removable, or the front 13 may be open, such that it is closed by the mounting plate 5 and front face 9. The separator 11c may be omitted from the base unit 3, or multiple separators may be provided to define a number of different volumes. The use of the rear cover 7 is optional, and this may be omitted so that the front plate 9 is open at its back. This will still be secured to the mounting plate 7 in the same manner. In the example discussed above, an opening 19, 55 is provided through the front face 13 of the base unit 3, the mounting plate 5 and rear cover 7 for connection of wires from the base unit 3 to the front plate 9. This is by way of example, the openings may be closed by connectable plugs, as discussed above. Furthermore, any number of openings may be provided. In the example discussed above, the opening 21 in the mounting plate is substantially the same size as the front face 13 of the base unit 3. However, this is by way of example only. The body 27 of the mounting plate 5 may be substantially solid, with the aperture 21 aligned with the apertures 19, 55 in the base unit 3 and rear cover 7. In the example discussed above, tabs 39, 40, 41, 42 extend over the aperture 21 in the mounting 5 plate to locate the mounting plate 5 relative to the base unit 3. This is by way of example only, and various other locating features may be used. For example, the front face 13 of the base unit 3, and rear face of the mounting plate 5 may be provided with engaging projections or ledges / recesses. Any suitable means may be used to fix the base unit 3 or mounting plate to the wall instead of or as well as screws. In some examples, the screw holes 57a,b may comprise elongate openings to provide greater flexibility in the fixing of the mounting plate 3 to the wall. The connections between the base unit 3 and mounting plate 5, the rear cover 7 and front plate 9 and the front plate 9 and mounting plate 5 discussed above are given by way of example only. The person skilled in the art will appreciate that any suitable means for connecting the parts together can be used. It will be appreciated that the connection means should be releasable, to allow access to the base unit 3 for maintenance and remote use of the front plate 9, if desired. The connections may be formed by, for example, screws, rivets, interengaging projections (such as snap fit or click fit), latches, clips, or any other suitable releasable connection. Optionally, a seal may be provided between the mounting plate 5 and the front cover 9, to prevent ingress of water. A seat may be provided in the form of a ledge which locates the seal. In the examples discussed above, the base unit 3 is assembled during manufacture, and the rear cover 7 is also secured to the front cover 9 during manufacture. This is by way of example, It may be that the installer assembles one or both of these parts on site. Likewise, the order of installation discussed above is given by way of example only. It may be, for example, that the base unit 3 is provided in the recess in the wall before the mounting plate 5 is secured to the base unit. The heating system 100 shown in Figure 6 is given by way of example. Any type of permanently installed heating device 102 may be controlled by the heating system. Furthermore, each relay 106a-c may be connected to two or more heating devices (for example a number of boilers 102a or underfloor heating elements 102b) that are controlled together. Furthermore, the same type of heating elements 102 may be controlled by different relays 106 to, for example, provide heating of different zones. Likewise, there need not be a one-to-one correspondence between relays 106 and temperature sensors 104. Any number of temperature sensors may be provided. For example, a single temperature sensor 104 may be used to control a number of heating devices 102a-c. In some examples, the correspondence between each temperature sensor 104a-c and each relay 106a-c may be fixed. However, in other examples, the communication interface 108 enables a user to select which relay 106a-c is controlled by which temperature sensor 104a-c. This may be controlled in software, which allows the user to set up which temperature sensor 104a-c controls which relay 106a-c, or may be set up in the physical connections, which allows an installer to set up or change which temperature sensor 104a-c controls which relay 106a-c. In further examples, one or more relays may be controlled without connection to the temperature sensor. In this case, the relay simply functions as a timer. In the example discussed above, the data and power connections between the base unit 3, and the heating devices 102a-c temperature sensors 104a-c, front plate 9 and user devices 128a,b are described as wireless or wired for the front plate 9. It will be appreciated that any of these connections may be provided by wired connections rather than wireless. In the examples discussed above, the control of the relays 106 is determined entirely in the base unit 3. It will be appreciated that at least part of the signal processing and / or memory may be distributed to a remote processor or memory, separate from the base unit and front plate 9, in communication by a wired or wireless connection. In the above example, the temperature sensors are provided separately to the front plate 9 and base unit 3. In other examples, the temperature sensors may be provided in the base unit 3 or front plate 9. In further examples multiple temperatures sensors may be provided, within the base 3 and / or front plate 9 and externally.

Claims

1. A thermostat unit comprising:a base unit arranged to be recessed into a surface, the base unit enclosing one or more heating relays and control electronics for operating one or more heating systems based on a set temperature and a measured temperature;a mounting plate securable to the base unit;a first front plate comprising a user interface arranged to forward user input to the control electronics; anda second front plate comprising a decorative front plate,wherein the first front plate and second front plate are releasably securable to the mounting plate, such that one of the first front plate and the second front plate is fitted to the mounting plate on installation.

2. A thermostat unit as claimed in claim 1, wherein the base unit comprises wireless communications means for communicating with one or more wireless devices, different to the first front plate, each comprising a user interface to forward user input to the control electronics.

3. A thermostat unit as claimed in claim 2, wherein at least one user interface is provided by a mobile phone application.

4. A thermostat unit as claimed in claim 2 or claim 3, only the user interface provided by the one or more wireless devices is used to operate the one or more heating systems when the second front plate is used to assemble the thermostat unit.

5. A thermostat unit as claimed in any preceding claim, wherein the user interface in the first front plate is only operational when the first front plate is fitted on the mounting plate and base unit.

6. A thermostat unit as claimed in any preceding claim wherein the user interface only receives user commands and forward them to the control electronics in thebase unit and receives status information from the control electronics in the base unit for display.

7. A thermostat unit as claimed in any preceding claim, wherein the user interfacein the first front plate is in communication with the control electronics by a short range wireless connection.

8. A thermostat unit as claimed in any of claim 1 to 6, wherein the user interface in the first front plate is in communication with the control electronics by a physical connection through the mounting plate.

9. A thermostat unit as claimed in any preceding claim, comprising a cover plate, securable to a rear of the first front plate, to enclose the electronics of the user interface.

10. A thermostat unit as claimed in any preceding claim, wherein the mounting plate is securable to the base unit by interengaging projections or clips.

11. A thermostat unit as claimed in claim 11, wherein the interengaging projections or clips are positioned at a peripheral edge of the base unit.

12. A thermostat unit as claimed in claim 10 claim 11, wherein the interengaging projections or clips are rotationally asymmetric around the base unit, to control the relative orientation between the base unit and the mounting plate.

13. A thermostat as unit in any of claim 10 to 12, wherein the mounting plate is securable to the wall through one or more screw holes, arranged outside the interengaging projections.

14. A thermostat unit as claimed in any preceding claim, wherein the front plate is securable to the mounting plate by a captive screw.temperature sensor, and a relay output associated with one or more heating devices.

16. A thermostat unit as claimed in claim 15, wherein each temperature sensor is selectively coupled to any one of the relays.

17. A thermostat unit as claimed in claim 15 or claim 16, wherein the or each heating relay is disconnectable from the temperature sensor, such that the thermostat acts as a timer switch.

18. A thermostat unit as claimed in any preceding claim, wherein the relays are able to control one or more of the following:underfloor heating elements, towel rail elements, radiators, electric boilers, gas boilers, immersion heaters and central heating / hot water valves.

19. A thermostat unit as claimed in any preceding claim, wherein the relays are able to control one or more zones of a heating system, with a separate relay and temperature sensor for each zone.

20. A kit comprising:a base unit enclosing one or more heating relays and control electronics for operating one or more heating systems based on a set temperature and a measured temperature;a mounting plate securable to the base unit;a first front plate comprising a first user interface arranged to forward user input to the control electronics for operation of the one or more heating systems; anda second front plate comprising a decorative plate, wherein the first front plate and second front plate are releasably securable to the mounting plate;wherein when first user interface is only operational when the first front plate is secured to the mounting plate; andwherein when the second front plate is secured to the mounting plate, a second user interface is provided, through a wireless device in communication with the control electronics.

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