GB2390142A

GB2390142A - Instantaneous water heater switch

Info

Publication number: GB2390142A
Application number: GB0314020A
Authority: GB
Inventors: Dominic George Webber; Robin Craig Cocker; Peter Georg Laitenberger
Original assignee: Aqualisa Products Ltd
Current assignee: Aqualisa Products Ltd
Priority date: 2002-06-24
Filing date: 2003-06-17
Publication date: 2003-12-31
Anticipated expiration: 2023-06-17
Also published as: GB2390142B; GB2390666A; GB0214536D0; GB0314020D0

Abstract

The water heater has a main valve (20, figure 2a) that is operated by a push button 22a to control the presence or absence of water at a flow rate control valve. One of two interchangeable on/off modules, 50a or 50b, may be provided to control the water flow. The on/off module 50a is a mechanical arrangement that includes a mechanical actuation member 76, a rotatable cam member 82, two springs 84 and 90, a housing 74, and attachment means 78 for the valve. The on/off module 50b is an electrical arrangement that includes an electrical actuation member such as a solenoid 52, a cantilever 56, an axially movable member 60, a housing 54, and attachment means 62 for the valve. The push button may consist of a push-push mechanism that moves the actuation member in opposite directions for consecutive pushes.

Description

2390 1 42

-1 INSTANTANEOUS WATER HEATER

The present invention relates to an instantaneous water heater, in particular an instantaneous water heater for a shower whereby the on/off mechanism is simplified S and improved.

A great variety of different types of instantaneous water heater are known.

These may be used in conjunction with a shower such that, when a user turns on a flow of water to the shower, the water is instantaneously heated to a desired temperature. Often, temperature control is achieved by varying the water flow rate 10 through the heater can of the instantaneous water heater.

It is known to provide instantaneous water heaters with various controls for the water flow. On the one hand, a manually rotatable on/off valve may be provided together with a pressure sensitive switch for providing power to electrical heating elements when water is flowing. On the other hand, the on/off valve and heating 1 S elements can be controlled electrically with a switch on the front cover of the instantaneous water heater.

Manually rotatable control valves provide relative cheap implementation, but are less desirable to the user. In contrast, electrical/solenoid operation provides more desirable operation for the user, but is more complicated and expensive.

20 Of course, different consumers will have different priorities and, hence, it is desirable to provide both instantaneous water heaters which are relatively inexpensive and those which provide improved functionality. Unfortunately, to provide both the mechanical arrangement and the electrical arrangement described above in the same product range, it is necessary to provide a large number of 25 ditterent components, thereby adding further to the overall cost.

It is an object of the present invention to overcome or at least reduce these problems. According to the present invention, there is provided a method of constructing an instantaneous water heater, the method including: 30 providing a main valve for allowing or preventing water flow through the water heater;

-2 providing a movable member for controlling the main valve; providing a user operable actuator t'or moving said member; and providing, thereby incorporating, the user operable actuator in an interchangeable on/off module; wherein 5 a plurality of interchangeable on/off modules are provided, at least one interchangeable on/off module having a mechanical user operable actuator and at least another interchangeable on/off module having an electrical user operable actuator. According to the present invention, there is also provided an instantaneous 10 water heater for a shower including: a main valve for allowing or preventing water flow through the water heater; a moveable member for controlling the main valve; and an interchangeable on/off module having a user operable actuator for moving said member, the user operable actuator being one of a mechanical actuator and an 15 electrical actuator and the on/off module being interchangeable with another on/off module having the other of the mechanical actuator and the electrical actuator.

Thus, since both the mechanical actuator and the electrical actuator move the member in order to operate the main valve, mechanical and electrically actuated instantaneous water heaters may be provided in the same product range without the 20 need for a large number of different components. In particular, the same main valve may be provided irrespective of whether the system operates mechanically or electrically. It is only necessary to assemble the instantaneous water heater with an appropriate one of the interchangeable on/ot'f modules, whether they be self-

contained units or assemblies of components. In this way, it becomes possible to 25 provide a larger range of products having a range of prices in accordance with the demands of consumers.

Prel'erably, the instantaneous water heater further includes a pilot valve for controlling the main valve, the member operating the pilot valve.

In this way, only a relatively small force is required to move the member, 30 thereby facilitating its use for both mechanical and electrical actuators. There is no

-3 need for the arm itself to directly drive the main valve so as to allow or prevent water flow. It is well known to use pilot valves to operate main valves by opening or closing passages exposing the main valves to different pressures. Any suitable 5 construction can be used with the present invention.

Preferably, the instantaneous water heater further includes guide walls for defining a water flow path wherein the member extends from inside to outside the guide walls.

In other words, where the pilot valve opens and closes a water passage from 10 inside the water flow path, the member extends from the pilot valve inside the water flow path to allow direct operation from outside the water flow path.

Preferably, the guide walls define a control aperture through which said member extends, the control aperture forming a sliding seal with the arm.

Preferably, the electrical actuator has a solenoid and a cantilever, the 15 cantilever being connected at one end to the member and at the other end to an armature of the solenoid such that the solenoid is located remotely from the member and is operable to move the member so as to control the main valve.

Thus, in contrast to previous designs intended only for use with solenoid operation, the solenoid is not located directly adjacent the main valve. The valve 20 includes a linkage, i.e. the member, allowing mechanical operation or operation by the solenoid. By use of the cantilever, the solenoid can be located remotely from the valve, thereby allowing greater overall design flexibility for the instantaneous water heater. Preferably, the instantaneous water heater further includes an electrical switch 95 connected electrically to the solenoid tor operating the solenoid and, hence, the main valve. The switch may be freely positioned anywhere in the front cover of the instantaneous water heater.

Preferably, the instantaneous water heater further includes a push button 30 which controls the main valve to allow and prevent water flow with consecutive pushes.

The push button may include the electrical switch for the solenoid or may be a mechanical device for controlling the main valve. By providing a push-push operation such that the water heater is turned on and off by consecutive pushes of the push button, it is possible to provide the user with the same simple intuitive user 5 interface for both electrically and mechanically actuated arrangements. This gives the mechanically actuated arrangements an improved user interface and desirability and gives the opportunity of reducing the overall cost of the range by allowing greater interchangeability and of providing other manufacturing/ logistical benefits.

Preferably, the mechanical actuator has a push-push mechanism which moves 10 said member in opposite respective directions for consecutive pushes of the push button. In other words, consecutive pushes result in the member moving in one direction to control the main valve to allow water flow and in the opposite direction to control the main valve to prevent water flow.

15 This mechanism allows the instantaneous water heater to be provided with a greatly improved user interface for the user. In particular, relatively cheap mechanical actuation is thus provided with the same push button operation as the more expensive electrical actuation.

According to the present invention, there is provided a method of 20 constructing an instantaneous water heater for a shower, the method including: providing a main valve for allowing or preventing water flow through the water heater; providing a moveable member for controlling the main valve; providing a push button; 25 providing a user operable actuator for moving said member; and constructing the user operable actuator as a mechanical actuator having a push-push mechanism which is operable mechanically by said push button to move said member in opposite respective directions for consecutive pushes of the push button. 30 According to the present invention, there is also provided an instantaneous water heater for a shower including: 4F

-5 a main valve for allowing or preventing water flow through the water heater; a moveable member for controlling the main valve; a push button; and a user operable actuator for moving said member; wherein 5 the user operable actuator is a mechanical actuator having a push-push mechanism which is operated mechanically by said push button to move said member in opposite respective directions for consecutive pushes of the push button.

As mentioned above, this provides a greatly improved user interface, particularly when compared to previous manual arrangements requiring manual 10 rotation of a main valve.

Preferably, the push-push mechanism includes a rotatable cam member which is stable in an even number of positions of rotation and includes a circumferential cam surface.

Preferably, the instantaneous water heater further includes a cam follower for 15 connection to the member, the cam follower following the cam surface such that, as the cam member is rotated between consecutive stable positions of rotation, the cam follower is moved between respective linear positions.

Thus, the member is moved so as to control the main valve, optionally by means of a pilot valve, as the rotatable cam member is rotated.

20 Consecutive positions of the rotatable cam member correspond to on and off states for the main valve such that it is sufficient for operation of the push button to push the rotatable cam member from one stable position the next stable position in order to change the state of the main valve.

The rotatable cam member can be bi-stable and have two stable positions of 25 rotation, one with the cam follower positioning the member to control the main valve to allow water flow and the other with the cam follower positioning the member to control the main valve to prevent water flow.

Preferably, the cam surface faces in a direction generally parallel to the axis of rotation of the cam member and the cam follower moves in a direction generally 3G parallel to the axis. In other words, the cam surface is a face cam.

For a bi-stable cam member, the cam surface thus extends from a first axial position to a second axial position over 180 and then back to the first axial position over the next 180 .

Preferably, the push-push mechanism includes a spring member for biasing -

5 the cam follower towards the cam surface.

in this way, the spring member provides the force for moving the cam follower and member in one of the two opposite directions.

Preferably, the cam member includes a circumferential registration surface and a resilient registration member for resiliently engaging the registration surface so 10 as to bias the cam member in opposite respective directions towards the stable positions of rotation either side of the intermediate positions.

In this way, it is not necessary for the user to operate the push button with any need for accuracy or complete indexing of the cam. The registration member ensures that the cam member is positioned accurately in either a position in which the main 15 valve is open or a position in which the main valve is closed. Since the resilient registration member biases the cam member in opposite directions either side of the intermediate positions, it is ensured that the cam member is always moved to the nearest either on or off position.

For the bi-stable mechanism, the circumferential registration surface may 20 include an elongate member positioned on a diameter of the cam member. The resilient registration member then preferably comprises a spring member resiliently engaging on either side of the elongate member such that the cam member will always return to one of two opposite orientations with the elongate side surfaces of the elongate member engaged by the spring.

25 Preferably, the cam member includes engagement surfaces and the push button extends, when pushed, to engage an engagement surface and rotate the cam member against the initial resisting bias of the resilient registration member until the cam member reaches the next intermediate position and the resilient registration member biases the cam member to the next stable position.

30 Hence, the push button is used mechanically to rotate the cam member between the required positions for opening or closing the main valve.

-7 Preferably, the push button can be pushed far enough to rotate the cam member past the next intermediate position.

This ensures that the cam member does not come to rest at an intermediate position where it is not positively biassed in either direction. The push button will 5 rotate the cam member past the next intermediate position such that the resilient registration member then ensures that the cam member is moved fully to the next correct stable position in which the main valve is either open or closed.

The invention will be more clearly understood from the following description,

giving by way of example only, with reference to the accompanying drawings, in 1 0 which: Figure 1 illustrates the front cover of an instantaneous water heater according to the present invention; Figures 2(a) and (b) illustrate exploded views of the functional components of instantaneous water heaters according to the present invention; 15 Figures 3(a) and (b) illustrate the assembled water heaters of Figures 2(a) and (b); Figures 4(a) and (b) illustrate the on/off module of the water heater of Figures 2(a) and 3(a); Figures 4(c) and (d) illustrate the on/off module of the water heater of Figures 20 2(b) and 3(b); Figure 4(e), (f) and (g) illustrate an alternative electrical on/off module; Figures S(a) and (b) illustrate the cam member of Figure 4(a); and Figures 6(a) to 8(c) illustrate operation of the on/off module of Figures 4(a) and (b).

25 As illustrated m Figure 1, an instantaneous water heater includes a front cover 2 including a water temperature control 4 and an on/off button 6.

The front cover 2 houses a number of functional components for providing hot water of a desired temperature.

Figures 2(a) and (b) illustrate suitable arrangements of components for use in 30 such a water heater.

-8 Water is provided to one of two alternative inlets 8 and 10. With the water heater running, the water is then channelled by a flow rate control valve 12 to the inside of a heater can 14. Within the heater can 14, the water flows up around the outside of a chimney 16 in contact with a heater element 18. The water then flows 5 down through the inside of the chimneyl6 and out of an outlet l9.

A main valve 20 operates under the control of a button 22a, 22b to control whether or not there is any flow from the inlets 8 or 10 to the flow rate control valve 12. The button 22a, 22b may actually control a pilot valve which in turn operates the main valve 20. Dependant upon the flow of water through the water heater, a 10 chamber 21 a, exposed to water pressure in the system, interacts with an arrangement 21b to move a rod 24. The rod 24 in turn operates an electrical switch 26 to turn on or off power to the heater element 18.

The flow rate control valve 12 may be operated by a rotatable member 28 so as to vary the flow rate through the heater can 14 and, hence, the outlet temperature.

15 Figures 2(a) and (b) and also Figures 3(a) and (b) are illustrated with alternative on/off modules 50a and 50b which are provided interchangeably with the rest of the apparatus.

The on/off module 50a of Figures 2(a) and 3(a) provides mechanical actuation of the main valve 20 and will be described further below. On the other 20 hand, the on/off module 50b of Figures 2(b) and 3(b) provides electrical actuation of the main valve 20 by means of a solenoid 52.

The solenoid 52 is preferably a DC solenoid. This has significant advantages in providing high forces without creating the audible buzz or hum associated with AC solenoids. In this respect, it is to be noted that previous solenoid operated valves 25 used an armature which was actually a slug within the water such that the buzz or hum was not a problem.

A rectifier may be provided for the solenoid and by using low voltage, it is possible to use electronic switching with a small and low-profile switch or button 22b. Bearing in mmd the wet environment in which the water heater is likely to be 30 installed, it is then not necessary to provide significant water shielding for the button 22b.

Figures 4(c) and (d) illustrate components of the orJoffmodule 50b.

The solenoid 52 is mounted to a module housing 54 which may be interchangeably mounted to the rest of the components illustrated in Figures 2(a) and (b). Within the housing 54 is provided a cantilever 56 which is supported by a pivot 5 58. The housing 54 also supports an axially movable actuation member 60 including a connection 62 for engaging a part of the valve assembly so as to control the main valve 20. Once engaged, the member 60 can be considered as part of a moveable member for controlling the main valve 20.

The member 60 is provided with a peripheral flange 64 which is engaged by a 10 slot 66 in one end of the cantilever 56. The other end of the cantilever 56 as illustrated includes a pivot opening 68 for receiving an extension to the armature 70 of the solenoid 52.

In use, actuation of the solenoid 52 will cause the armature 70 to pivot the cantilever 56 and hence move the member 60 along its axis. As mentioned above, 15 the member 60 is attached to the valve assembly. With the member 60 in one axial position, the main valve 20 is opened and with the member 60 in another opposite axial position, the main valve 20 is closed. Thus, by using the solenoid 52 to move the member between its two axial positions, the main valve 20 may be opened and closed. 20 As mentioned above, the on/off module 50b is interchangeable with the on/off module 50a employing mechanical actuation.

Figure 4(e) illustrates an assembly of components forming an alternative module 50c employing electrical actuation. Figure 4(f) illustrates the module 50c separated from the rest of the water heater and Figure 4(g) illustrates the components 25 of the module 50c.

A solenoid 152 is mounted to a bracket 153 by means of a clamp 154. As Illustrated, the bracket 153 is attached to the rest of the water heater structure by means of a boss 155 formed as part of that structure.

cantilever 156 is supported by a pivot 158 at a position intermediate its two 30 ends. One end of 168 of the cantilever 156 is rotatably attached to an extension 170 of the armature of the solenoid 152. The other end 166 of the cantilever 156 is

-10 arranged to engage with an axially movable actuation member 160 equivalent to member 60 described above.

In use, actuation ofthe solenoid 152 will cause the armature extension 170 to pivot the cantilever 156 and hence move the member 160 along its axis. As 5 described above the member 160 may be attached to the valve assembly and? thus, used to open and close the main valve 20.

In the illustrated embodiment, a coil spring 159, wraps around the pivot 158 and includes one end 159a which abutts a wall of the cantilever. The coil spring 159 in this way biases the cantilever 156 in a direction so as to close the main valve 20.

10 Only when the solenoid 152 is activated is the force of the coil spring 159 overcome and the main valve 20 opened.

The pivot 158 may be formed as part of the general valve housing and left redundant when other on/off modules, such as those described above and below, are used. Alternatively, the assembly of components conning module 50c may include a 15 housing component specific to that module and including the pivot 158.

As mentioned above, the on/module 50c is interchangeable with the on/off module 50a employing mechanical actuation.

As illustrated in Figures 4(a) and (b), the housing 74 of the on/offmodule 50a has the same general form as module 50b for mating with the rest of the components 20 of the instantaneous water heater and similarly can be used in place of the assembly forming module 50c.

It is provided with an actuation member 76 which is axially and slidably supported in the housing 74 in the same relative position as the member 60 in the housing 54. It also includes similar means 78 for attachment to valve components.

25 Members 60, 76 and 160 may all be identical, thereby further simplifying production and the interchangeability of the modules 50a, 50b and 50c. Indeed, members 60,76, 160 may actually be extensions of the rod controlling a pilot valve and may include features specific to more than one module 60, 76,160, for example for connecting with a cantilever or a cam (to be described below).

30 Thus, the on/off module 50a may be interchangeably assembled in the instantaneous water heater with the on/off module 50b and 50c. Operation of the

-11 push button 22a will operate the member 76 in the same manner as actuation of the solenoid 52, 152 will operate member 60, 160.

Operation of the mechanism of on/offmodule 50a will be described in further detail below. However, referring to Figure 4(a), it will be seen that the push button 5 22a includes an extension 80 which engages with a rotatable Cain member 82.

Against the resistance of a spring 84, the push button 22a may be pushed such that the extension portion 80 rotates the cam member 82 by a predetermined angle.

As illustrated, the rotatable cam member 82 is provided with a downwardly facing cam surface 86, ie a face cam, and the member 76 is provided with a cam 10 follower 88.

A spring 90 is also provided to ensure that the cam follower 88 engages the cam surface 86.

Thus, as the rotatable cam member 82 rotates, due to the varying axial position of the surface 86, the member 76 is moved axially so as to control the main 15 valve 20.

As will be described further below, the illustrated cam member 82 is bistable and has an elongate section across its diameter towards the upper surface. A resilient registration member 92 such as a spring engages the surfaces of the cam member 82 to ensure that the cam member 82 is always biased to either of two opposite 20 orientations. These orientations correspond to positions of the member 76 for the main valve 20 to be open or closed.

Figures 5(a) and (b) illustrate in greater detail the cam member 82.

The cam member 82 includes a central region 91 on which the cam surface 86 is formed. The cam member 82 is rotatable about a central axis 94 and the cam 25 surface 86 is formed around a circumference of the central region 91. The cam surface 86 faces in an axial direction, i.e. downwardly as illustrated. Around the circumference, the cam surface varies in an axial location such that, with reference to Figure 4(a) the cam follower 88 and member 76 are moved axially to and fro.

The illustrated embodiment is bi-stable such that the cam member 82 is 30 resiliently biased to come to rest in two rotational positions. Corresponding to these positions, the cam surface 86 extends between two axial locations, such that in one r

-12 rotational position of the cam member 82, the cam follower 88 is at one axial position and at the other rotational position of the cam member 82, the cam follower 88 is at the other axial position. To achieve this, the cam surface 86 may have a generally planar surface which is slanted with respect to the axis 94.

5 Above the central region 91 is a registration region 96 including a registration surface 98 and above the registration region 96 is an engagement region 100 with an engagement surface 102.

With reference to Figure 4(a), the extension 80 of the button 22a is intended to engage with the engagement surface 102 of the engagement region 100. In 10 particular, it engages in a position offset from registration surface 98 in the axis 94 so as to rotate the cam member 82 upon depression of the button 22a. In the preferred embodiment, it is intended that the button 22a will only require 6mm of movement to rotate the cam member 82 to its next stable position. As will be described below, this is achieved with the resilient registration spring 92 which acts on the registration 15 surface 98 of the registration region 96 so as to bias the cam member 82 to its next stable positions.

The operation of the cam member 82 is illustrated schematically in Figures 6(a) to (c), 7(a) to (c) and 8(a) to (c).

In the state illustrated in Figure 6(a), 7(a) and 8(a), the cam follower 88 and 20 member 76 extend axially furthest towards the valve components. In other words, the cam surface is positioned axially towards the valve components and the central region 92 is at its thinnest.

Figure 6(a) illustrates the engagement region 100 at the top of the cam member 82. As illustrated, depressing button 22a causes the extension 80 to engage 25 the engagement region 100 and to rotate the cam member 82 to the position as illustrated in Figure 6(b).

Figure 7(a) illustrates schematically the registration region 96 below the engagement region 100. As illustrated, the resilient spring 92 contacts either side of the registration region 96. As the cam member 82 is rotated, the registration region 30 96 separates the anns of the spring 92 as illustrated in Figure 7(b). Thus, rotation of the cam member 82 is against the resilient force of the spring 92.

r

-13 At this point, the cam surface 86 and cam follower 88 are at an intermediate position. It will be seen that there is an intermediate position beyond which the spring 92 acts on the registration surface 98 of the registration region to rotate the cam 5 member 82 to the next rotational stable position. Hence, without any further depression of button 22a, the spring 92 acts to rotate the cam member 82 to the next stable position as illustrated in Figures 6(c), 7(c) and 8(c).

At this position, as illustrated in Figure 8(c), the cam follower 88 and member 76 are axially located further away from the valve components.

l 0 The two rotationally stable positions and the two corresponding axial positions for the cam follower 88 and member 76 correspond respectively to the main valve being opened and closed. Hence, with consecutive pushes of the button 22a, the cam member 82 is rotated between its rotationally stable positions and the main valve is opened and closed.

15 It is sufficient for the button 22a and extension 80 to move far enough to rotate the cam member by more than 90 . Once this angle has been exceeded, the spring 92 ensures that the cam member 82 is moved through the full l 80 .

In this preferred embodiment, the cam member has stable positions at l 80 intervals. This allows plenty of movement of the components and reduces the need 20 for accurate tolerances. However, the cam member 82 could be provided with any even number of stable positions allowing the cam follower 88 and member 76 to move consecutively between their two axial positions. Of course, the cam surface 86 would also extend axially in opposite directions a corresponding number of times around the circumference. In that case, an appropriate arrangement of engagement 25 surfaces (for instance more like teeth) would be required and the registration region would have to be designed accordingly (for instance having a generally square, hexagonal, octagonal etc. cross section).

Claims

-14 CLA1MS

1. An instantaneous water heater for a shower including: a main valve tor allowing or preventing water flow through the water heater; 5 a movable member for controlling the main valve; and an interchangeable on/off module having a user operable actuator for moving said member, the user operable actuator being one of a mechanical actuator and an electrical actuator and the orr/oE module being interchangeable with another on/off module having the other of the mechanical actuator and the electrical actuator.

l O 2. An instantaneous water heater according to claim 1 wherein the electrical actuator has a solenoid and a cantilever, the cantilever being connected at one end to said member and at the other end to an armature of the solenoid such that the solenoid is located remotely from said member and is operable to move said member so as to control the main valve.

15 3. An instantaneous water heater according to claim 2 further including an electrical switch connected electrically to said solenoid for operating said solenoid and, hence, said main valve.

4. An instantaneous water heater according to claim I, 2 or 3 further including: 20 a push button which controls the main valve to allow and prevent water flow with consecutive pushes.

5. An instantaneous water heater according to claim 4 wherein the mechanical actuator has a push-push mechanism which moves said member in opposite respective directions lor consecutive pushes of the push button.

25 6. An instantaneous water heater for a shower including: a main valve for allowing or preventing water flow through the water heater; a moveable member for controlling the main valve; a push button; and a user operable actuator for moving said member; wherein c

-15 the user operable actuator is a mechanical actuator having a pushpush mechanism which is operated mechanically by said push button to move said member in opposite respective directions for consecutive pushes of the push button.

7. An instantaneous water heater according to claim 5 or 6 wherein the 5 push-push mechanism includes: a rotatable cam member which is stable in an even number of positions of rotation and includes a circumferential cam surface.

8. An instantaneous water heater according to claim 7 further including: a cam follower for connection to said arm, the cam follower following said 10 cam surface such that as said cam member is rotated between consecutive stable positions of rotation said cam follower is moved between respective linear positions.

9. An instantaneous water heater according to claim 7 or 8 wherein the rotatable cam member is bistable and has two stable positions of rotation, one with the cam follower positioning the member to control the main valve to allow water I S flow and the other with the cam follower positioning the member to control the main valve to prevent water flow.

10. An instantaneous water heater according to claim 8 or 9 wherein the cam surface faces in a direction generally parallel to the axis of rotation of the cam member and the cam follower moves in a direction generally parallel to the axis.

20 1 1. An instantaneous water heater according to claim 9 or 10 wherein the push-push mechanism includes a spring member for biasing the cam follower towards the cam surface.

12. An instantaneous water heater according to any one of claims 7 to I 1 wherein the cam member includes a circumferential registration surface and a 25 resilient registration member for resiliently engaging said registration surface so as hulas the cam member in opposite respective directions towards the stable positions of rotation either side of intermediate positions.

13. An instantaneous water heater according to claim 12 wherein the cam member includes engagement surfaces and the push button extends, when pushed, to 30 engage an engagement surface and rotate the cam member against the initial resisting bias of the resilient registration member until the cam member reaches the next

-16 intermediate position and the resilient registration member biases the cam member to the next stable position.

14. An instantaneous water heater according to claim 13 wherein the push button can be pushed far enough to rotate the cam member past the next intermediate S position.

I S. An instantaneous water heater according to any preceding claim further including: a pilot valve for controlling the main valve, said member operating said pilot valve. 10 16. An instantaneous water heater according to any preceding claim further including: guide walls for defining a water flow path; wherein the member extends *om inside to outside the guide walls.

17. An instantaneous water heater according to claim 16 wherein the 15 guide walls define a control aperture through which said member extends, the control aperture forming a sliding seal with said member.

18. A method of constructing an instantaneous water heater, the method including: providing a main valve for allowing or preventing water flow through the 20 water heater; providing a moveable member for controlling the main valve; providing a user operable actuator t'or moving said member; and providing the user operable actuator in an interchangeable on/ot'f module; wherem 25 a plurality of interchangeable on/off modules are provided, at least one interchangeable on/ot'f module having a mechanical user operable actuator and at least another interchangeable on/off module having an electrical user operable actuator. 19. A method of constructing an instantaneous water heater for a shower, 30 the method including:

-17 providing a main valve for allowing or preventing water flow through the water heater; providing a moveable member for controlling the main valve; providing a push button; 5 providing a user operable actuator for moving said member; and constructing the user operable actuator as a mechanical actuator having a push-push mechanism which is operable mechanically by said push button to move said member in opposite respective directions for consecutive pushes of the push button. l O 20. An instantaneous water heater constructed and arranged substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings. 21. A method of constructing an instantaneous water heater substantially as hereinbefore described with reference to and as illustrated by the accompanying 1 5 drawings.

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