The present invention relates to a contact temperature sensor for fitment to a hot water cylinder. In particular the present invention relates to a temperature sensor that can be retro fitted to a domestic hot water cylinder assembly in an array in order to determine the temperature of the water within the cylinder at different points.

It is desirable to obtain information about the state of charge of a hot water tank, i.e. how much hot water is in the tank and the temperature of that water, in order to, for example, optimise the amount of energy used to meet the hot water requirements of a house. Also, that information can be used to optimise when the water is heated, for example to make use of a lower cost energy tariff that might be available at a particular time over a twenty four period.

Accordingly, the present invention provides a contact temperature sensor arrangement comprising, along an axis X-X, a wired contact temperature sensor at a proximal end and an insert at a distal end and an abutment surface on the wired contact temperature sensor, wherein the insert has a resiliently deformable anchor that, during a fitting step, reduces in length along axis X-X and reduces in width in a direction perpendicular to axis X-X, wherein the reduction in width takes place along at least a portion of its length, wherein the fitting step entails the application of a fitment force along the direction of axis X-X in a proximal direction and a constraint of movement of the insert along the direction of axis X-X caused by the abutment .

Preferably, the insert has an insert anchoring portion and an insert compressing portion.

More preferably, at least the external portion of the insert is made of a resiliently deformable material.

Alternatively, the insert is made entirely of a resiliently deformable material.

Preferably, the insert is made entirely from a resiliently deformable polyurethane foam.

The insert may be made entirely from a resiliently deformable polyurethane foam with a density of 25kg/m3.

The foam used for the insert should also have a low thermal conductivity to reduce any heat loss from the hot water tank. Preferably, the insert, when not in use, has at least one dimension in a direction perpendicular to axis X-X that reduces along the X-X axis from the distal end to the proximal end.

Preferably, the insert has the shape of a cone or the frustum of a cone and wherein the longitudinal axis of the cone is co-axial with the axis X-X and the base of the cone is located at the distal end.

An insert in the form or a cone, or the frustrum of a cone, is advantageous because it assists with alignment of the sensor. The insert is compressed when it is inserted into the hole in the insulating jacket. The free space between the tip end of the cone and the wall of the hole allows the insert to change its shape in a more even way around the longitudinal axis X-X, thus avoiding any uneven change in form that might bias the sensor away from an orientation that is perpendicular to the wall of the water tank.

For this reason, it is the case that if the insert is a frustrum of a cone then it is preferred that the diameter of the frustum is less than the diameter of the hole in the insulating jacket.

In a preferred embodiment, the maximum width of the insert in use is lower than the maximum width of the insert when it is not in use.

Preferably, the insert has a through bore aligned with its longitudinal axis.

Preferably, the abutment is a push-on washer.

Preferably, each of the abutment and the insert is provided with a through bore and wherein the temperature sensor, the temperature sensor cable, the abutment and the insert form a sub-assembly with the temperature sensor cable extending in a distal direction from the temperature sensor and the abutment and the anchoring element threaded on to the temperature sensor cable, the abutment located proximally relative to the insert and wherein the temperature sensor cable passes through each through bore.

Preferably there is a centring element located along the axis X-X and wherein the centring element has a through bore within which, in use, the temperature sensor can be at least partially located.

Preferably the compressive strength of the material of the centring element is greater than the compressive strength of the material of the anchoring element. Preferably, the centring element has a distally directed abutment face and the insert has a proximally directed abutment face and wherein a force applied to the insert along the axis X- X in a proximal direction is transferred to the centring element and then to the abutment. Preferably, at least a section of the insert is formed from a material that has a low thermal conductivity. This is advantageous because it helps to maintain the integrity of the insulating jacket surrounding the hot water tank.

According to a second aspect of the present invention there is provided a method of fitting a contact temperature sensor arrangement to a hot water cylinder assembly having a tank with a tank wall and an insulation jacket comprising the steps of: drilling a blind hole through the insulation jacket up to, but not through, the tank wall to create a cylindrical fitment bore with a longitudinal axis X-X having a proximal end adjacent to the tank wall and a distal end adjacent to the external surface of the insulation jacket locating the contact temperature sensor arrangement within the fitment bore applying an axial securing force in a proximal direction along the axis X-X wherein the sensor arrangement is moved within the bore in a proximal direction so that a contact face of the temperature sensor is brought into contact with the tank wall and wherein a compressive force is applied to the insert such that at least a portion of the insert expands in a direction perpendicular to the axis X-X, the external surface of the insert becoming releasably mechanically engaged with the internal surface of the fitment bore, wherein upon removal of the axial securing force the insert exerts a proximally directed force on to the abutment in order to maintain the contact face of the sensor in contact with the tank wall.

Preferably, the cables of the sensor arrangements are attached to a wiring loom and to a control system.

According to a third aspect of the present invention there is provided a hot water cylinder assembly fitted with a plurality of contact temperature sensor arrangements wherein the hot water cylinder assembly comprises a water tank with a tank wall and an insulating jacket a plurality of temperature sensor each sensor located within a fitment bore in the insulating jacket the temperature sensors anchored within the fitment bores by an insert that is releasably mechanically engaged with the wall of the fitment bore.

Preferably, at least one insert is in the form of a cone or the frustrum of a cone and the diameter of the base of the cone of the insert of each contact temperature sensor arrangement prior to fitment into the fitment bore is greater than the diameter of the fitment bore. According to a fourth aspect of the present invention there is provided a kit of parts for a temperature sensor arrangement comprising a wired contact temperature sensor with a temperature sensor cable, an abutment and an insert.

Figure 1 is a cross sectional view of a preferred embodiment of the contact temperature sensor arrangement in a state immediately prior to being fitted into place;

Figure 2 is a cross sectional view of a preferred embodiment of the contact temperature sensor arrangement in a state when fitted into place;

Figure 3 is an exploded view of the components of a second embodiment of the contact temperature sensor arrangement;

Figure 4 is a side view of an assembled contact temperature sensor arrangement of the second embodiment of Figure 3 prior to fitment;

Figure 5 is a side view of an assembled contact temperature sensor arrangement of Figures 3 and 4 prior to fitment, but with an axial load applied along the X-X longitudinal axis (illustrated for the purposes of showing how the foam insert will expand in diameter when reduced in length, if unconstrained);

Figure 6 is a side view of the contact temperature sensor arrangement of Figure 4 when it is located within the fitment bore in the insulating jacket of a hot water cylinder assembly after a first fitting step and prior to the application of an axially directed force;

Figure 7 is a side view of the contact temperature sensor arrangement of Figure 4 when it is located within the fitment bore in the insulating jacket of a hot water cylinder assembly after a second fitting step in which an axially directed force is applied to the insert to force the temperature sensor into contact with the wall of the tank and to deform the insert such that it anchors the sensor arrangement within the fitment bore;

Figure 8 is a cross-sectional view through the contact temperature sensor arrangement of Figure 6;

Figure 9 is a cross-sectional view through the contact temperature sensor arrangement of Figure 7; and Figure 10 is a third embodiment of a contact temperature sensor arrangement according to the present invention, similar to the first embodiment, but providing with a centring bead;

Figure 11 is the third embodiment of a contact temperature sensor arrangement according to the present invention shown in a state when fitted into place; and

Figure 12 is a cross-sectional view through a hot water cylinder assembly fitted with an array of contact temperature sensors according to the second embodiment, a wiring loom and a control system.

SPECIFIC DESCRIPTION

A preferred embodiment of a contact temperature sensor arrangement according to the present invention is shown in Figure 1. The contact temperature sensor arrangement 1 comprises five components. A wired temperature sensor 3 having a sensor cable 5 that facilitates electrical connection between the sensor arrangement 1 and the control system 7 (shown schematically in Figure 11), a metal push-on lock washer 9, a polyurethane foam insert 11 and a rubber grommet 13. The five components are arranged along an axis X-X in the above stated order from an end that is, in use, proximal to the tank wall 35 of the tank 33 of the hot water cylinder assembly 31 to an end that is, in use, distal to the tank wall 35.

The wired temperature sensor 3 is of a known type. It is cylindrical with a diameter of 4mm and a length of 20mm. A flat contact face 15 is provided at its proximal end. The temperature sensor cable 5 is attached to the sensor 3 at its distal end and extends therefrom. Typically, the cable 5 is offset from the axis X-X.

The push-on lock washer 9 is of standard form, typically made from stainless steel, and is selected to have a through bore 17 with a diameter that is complementary to the external diameter of the sensor 3. The through bore 17 has a castellated internal form created by resilient tabs 19 (not shown). In assembly, the push-on lock washer 9 is pushed on to the sensor 3, the resilient tabs 19 deflect and grip the external surface of the sensor 3 and the push-on lock washer 9 becomes securely fastened to the sensor 3 halfway along its length, such that it is able to resist forces applied to it in a proximal direction parallel to axis X-X.

The insert 11 is made from a polyurethane foam with a density of around 25kg/m3. elongate and conical in shape with a thrust surface 21 at its proximal end and a through bore 23 along its longitudinal axis which is sized to enable the cable 5 to pass through the insert 11. In assembly the insert 11 is pushed over the cable 5 until the thrust surface 21 abuts the distal end of the sensor 3 and the push-on lock washer 9. The insert 11 is made from a low modulus foam, for example an open cell polyurethane foam, and will deform elastically when it is subjected to a compressive axially applied force.

The grommet 13 is annular with a central bore 25 that is sized to allow the cable 5 to pass through it. In assembly the grommet 13 is passed over the cable 5 and rests against the distal face of the insert 11.

The diameters of the push-on lock washer 9, the insert 11 and the grommet 13 are selected according to the diameter of the fitment bore 27 that is made in a rigid foam insulation jacket 29 of a hot water cylinder assembly 31 (as shown in Figures 4, 5 and 6). The largest diameter of the element 11, i.e. the diameter of the base of the cone, is larger than the diameter of the fitment bore 27. The diameters of the sensor 3 and the push-on lock washer 9 are smaller than that of the fitment bore 27.

The length of the insert 11 is selected according to the length of the fitment bore 27, i.e. the distance between the external surface of the tank wall 35 of the tank 33 and the external surface 37 of the outer casing 39 of the hot water cylinder assembly 31. The insert 11 in an uncompressed state, i.e. before the application of an axial force, extends out from the outer casing 39, as shown in Figure 1.

The first stage in fitting the sensor arrangement 1 to the hot water cylinder assembly 31 is to drill a hole through the outer casing 39 and the rigid foam insulation jacket 29 (but not the tank wall 35) to create the fitment bore 27. The sensor arrangement 1 can then be located in an initial position within the fitment bore 27, as shown in Figure 1.

An axially directed securing force, in the proximal direction, is then applied to the distal end of the insert 11. In a first phase of application of the force the contact face 15 of the sensor 3 is brought into contact with the external surface of the tank wall 35. In a second phase of application of the securing force, the insert 11 begins to become compressed along the X-X axis, because it can no longer freely move axially in a proximal direction once the sensor 3 is abutting the tank wall 35 and the thrust surface 21 of the insert 11 has come into contact with the sensor 3 and the push-on lock washer 9. This axial compression of the insert 11 causes the bore 23 of the insert 11 to close up around the cable 5 and the body of the insert 11 to expand radially outwardly to close up the gap between the external surface of the insert 11 and the wall of the fitment bore 27. This is shown in Figure 2. In a compressed state the insert 11 has two portions which perform different purposes. The distal portion, insert anchoring portion 11a, has been compressed by the securing force and radially expanded and is in contact with the wall of the fitment bore 27. The insert anchoring portion 11a anchors the insert 11 to the wall of the fitment bore 27. The proximal portion, insert compressing portion 11b, has been compressed by the securing force and has transferred the compressive force to the sensor 3 and the push-on lock washer 9 to hold the sensor 3 in contact with the external surface of the tank wall 35. The insert compressing portion 11b cannot expand back to its pre fitment state (which might result in the sensor 3 coming out of contact with the tank wall 35), because the combination of the conical shape of the insert 11 and the anchoring of the insert 11 to the rigid foam insulation jacket 29 does not allow that to happen. In pressing the insert 11 against the fitment bore 27 the cellular structure of the foam of the insert 11 mechanically engages with the rigid foam of the insulating jacket 29 such that when the securing force is no longer applied the insert 11 retains a sufficient level of elastic deformation to ensure that the sensor 3 is held against the tank wall 35. The final step is to locate the grommet 13 within the hole drilled in the casing 39. The grommet 13 prevents chafing of the cable 5 against the casing 39.

The sensor arrangement 1 can be removed from the hot water cylinder assembly 31, for example to enable replacement of the sensor 3 if it fails. The grommet 13 is removed from the casing 39 and the insert 11 can be removed, for example by using a pair of needle nosed pliers, to grip the insert 11 and extract it, or by applying a distally directed pulling force to the sensor cable 5 to extract the insert 11. The insert 11 will elastically deform during this removal step thus preventing any damage to the fitment bore 27.

A second embodiment of a contact temperature sensor arrangement according to the present invention is shown in Figures 3 to 9. The contact temperature sensor arrangement 201 comprises six components. A wired temperature sensor 203 having a sensor cable 205 that facilitates electrical connection between the sensor arrangement 201 and the control system 7 (shown schematically in Figure 12), a push-on lock washer 209, a centring bead 210, an insert 211 and a grommet 213. The six components are arranged along an axis X-X in the above stated order from an end proximal to the tank wall 35 of the tank 33 of the hot water cylinder assembly 31 to an end distal to the tank wall 35.

The wired temperature sensor 203 is of a known type. It is cylindrical with a diameter of 4mm and a length of 20mm. A flat contact face 215 is provided at its proximal end. The temperature sensor cable 205 is attached to the sensor 203 at its distal end and extends therefrom. Typically the cable 205 is offset from the axis X-X.

The push-on lock washer 209 is of standard form, typically made from a metal, and is selected to have a washer through bore 212 with a diameter that is complementary to the external diameter of the sensor 203. The washer through bore 212 has a castellated internal form created by resilient tabs 219. In assembly, the push-on lock washer 209 is pushed on to the sensor 203, the resilient tabs 219 deflect and grip the external surface of the sensor 203 and the push-on lock washer 209 becomes securely fastened to the sensor 203 halfway along its length, such that it is able to resist forces applied to it in a proximal direction parallel to axis X- X.

The centring bead 210 is generally cylindrical in shape and it has a thrust surface 220 at its proximal end and a bead through bore 222 along its longitudinal axis which is sized to enable the sensor 203 to pass into the bead through bore 222. In assembly, the centring bead 210 is pushed over the cable 205 and the distal part of the sensor 203 until the thrust surface 220 abuts the push-on lock washer 209. The centring bead 210 is made from PVC and is thus able to resist compressive axially applied forces without any significant reduction in length.

The insert 211 is elongate and generally cylindrical in shape with a thrust surface 221 at its proximal end and a through bore 223 along its longitudinal axis which is sized to enable the cable 205 to pass through the insert 211. In assembly the insert 211 is pushed over the cable 205 until the thrust surface 221 abuts the centring bead 210. The insert 210 is made from a low modulus foam, for example an open cell polyurethane foam, and will deform elastically to increase in diameter when it is subjected to a compressive axially applied force.

The grommet 213 is annular with a central bore 225 that is sized to allow the cable 205 to pass through it. In assembly the grommet 213 is passed over the cable 205 and rests against the distal face of the insert 211.

The diameters of the push-on lock washer 209, the centring bead 210, the insert 211 and the grommet 213 are selected according to the diameter of the fitment bore 27 that is made in a rigid foam insulation jacket 29 of a hot water cylinder assembly 31 (as shown in Figures 6 to 9). The diameters of all of the six components are smaller than the diameter of the fitment bore 27. The centring bead 210 has a diameter that is very slightly smaller than the diameter of the fitment bore 27, i.e. to provide a close clearance fit relationship between the centring bead 210 and the fitment bore 27. The diameter of the insert 211 is slightly less than the diameter of the centring bead 210. The diameter of the push-on lock washer209 is less than the diameter of the centring bead 210.

The length of the insert 211 is selected according to the length of the fitment bore 27, i.e. the distance between the external surface of the wall 35 of the tank 33 and the external surface 37 of the outer casing 39 of the hot water cylinder assembly 31. The insert 211 in an uncompressed state, i.e. before the application of an axial force, extends out from the outer casing 39, as shown in Figure 6 and in Figure 8.

The first stage in fitting the sensor arrangement 201 to the hot water cylinder assembly 31 is to drill a hole through the outer casing 39 and the rigid foam insulation jacket 29 (but not the tank wall 35) to create the fitment bore 27.

The sensor arrangement 201 can then be located within the fitment bore 27, as shown in Figure 6 and Figure 8. The close clearance fit between the centring bead 210 and the fitment bore 27 ensures that the sensor 203 remains closely aligned to the axis X-X within the fitment bore 27.

An axially directed securing force, in the proximal direction, is then applied to the distal end of the insert 211. In a first phase of application of the force the contact face 215 of the sensor 203 is brought into contact with the external surface of the tank wall 35. In a second phase of application of the securing force the insert 211 is compressed along the X-X axis, because it can no longer move axially in a proximal direction once the sensor 203 is abutting the tank wall 35 and the thrust surface 221 of the insert 211 is abutting the centring bead 210. This axial compression of the insert 211 causes the bore 223 of the insert 211 to close up around the cable 205 and to expand radially outwardly to close up the gap between the external surface of the insert 211 and the wall of the fitment bore 27. In pressing the insert 211 against the fitment bore 27 the cellular structure of the foam of the insert 211 mechanically engages with the rigid foam of the insulating jacket 29 such that when the securing force is no longer applied the insert 211 retains a sufficient level of elastic deformation to ensure that the sensor 203 is held against the tank wall 35. The final step is to locate the grommet 213 within the hole drilled in the casing 39. The grommet 213 prevents chafing of the cable 205 against the casing 39.

The sensor arrangement 201 can be removed from the hot water cylinder assembly 31, for example to enable replacement of the sensor 203 if it fails. The grommet 213 is removed from the casing 39 and the insert 211 can be removed, for example by using a pair of needle nosed pliers, to grip the insert 211 and extract it, or by applying a distally directed pulling force to the sensor cable 205 to extract the insert 211. The insert 211 will elastically deform during this removal step thus preventing any damage to the fitment bore 27.

A third embodiment of a contact temperature sensor arrangement according to the present invention is shown in Figures 10 and 11. The contact temperature sensor arrangement 301 comprises six components. A wired temperature sensor 303 having a sensor cable 305 that facilitates electrical connection between the sensor arrangement 301 and the control system 7 (shown schematically in Figure 12), a push-on lock washer 309, a centring bead 310, an insert 311 and a grommet 313. The six components are arranged along an axis X-X in the above stated order from an end proximal to the tank wall 35 of the tank 33 of the hot water cylinder assembly 31 to an end distal to the tank wall 35.

The wired temperature sensor 303 is of a known type. It is cylindrical with a diameter of 4mm and a length of 20mm. A flat contact face 315 is provided at its proximal end. The temperature sensor cable 305 is attached to the sensor 303 at its distal end and extends therefrom. Typically the cable 305 is offset from the axis X-X.

The push-on lock washer 309 is of standard form, typically made from a metal, and is selected to have a washer through bore 312 with a diameter that is complementary to the external diameter of the sensor 303. The washer through bore 312 has a castellated internal form created by resilient tabs 319. In assembly, the push-on lock washer 309 is pushed on to the sensor 303, the resilient tabs 319 deflect and grip the external surface of the sensor 303 and the push-on lock washer 309 becomes securely fastened to the sensor 303 halfway along its length, such that it is able to resist forces applied to it in a proximal direction parallel to axis X- X.

The centring bead 310 is generally cylindrical in shape and it has a thrust surface 320 at its proximal end and a bead through bore 322 along its longitudinal axis which is sized to enable the sensor 303 to pass into the bead through bore 322. In assembly, the centring bead 310 is pushed over the cable 305 and the distal part of the sensor 303 until the thrust surface 320 abuts the push-on lock washer 309. The centring bead 210 is made from PVC and is thus able to resist compressive axially applied forces without any significant reduction in length.

The insert 311 is elongate and conical in shape with a thrust surface 321 at its proximal end and a through bore 323 along its longitudinal axis which is sized to enable the cable 305 to pass through the insert 311. In assembly the insert 311 is pushed over the cable 305 until the thrust surface 321 abuts the centring bead 310. The insert 311 is made from a low modulus foam, for example an open cell polyurethane foam, and will deform elastically to increase in diameter when it is subjected to a compressive axially applied force.

The grommet 313 is annular with a central bore 325 that is sized to allow the cable 305 to pass through it. In assembly the grommet 313 is passed over the cable 305 and rests against the distal face of the insert 311.

The diameters of the push-on lock washer 309, the centring bead 310, the insert 311 and the grommet 313 are selected according to the diameter of the fitment bore 27 that is made in a rigid foam insulation jacket 29 of a hot water cylinder assembly 31 (as shown in Figures 10 and 11). The largest diameter of the element 311, i.e. the diameter of the base of the cone, is larger than the diameter of the fitment bore 27. The diameters of the sensor 303, the centring bead 310 and the push-on lock washer 309 are smaller than that of the fitment bore 27. The centring bead 310 has a diameter that is very slightly smaller than the diameter of the fitment bore 27, i.e. to provide a close clearance fit relationship between the centring bead 210 and the fitment bore 27. The diameter of the insert 311 is slightly less than the diameter of the centring bead 310. The diameter of the push-on lock washer 309 is less than the diameter of the centring bead 310.

The length of the insert 311 is selected according to the length of the fitment bore 27, i.e. the distance between the external surface of the tank wall 35 of the tank 33 and the external surface 37 of the outer casing 39 of the hot water cylinder assembly 31. The insert 311 in an uncompressed state, i.e. before the application of an axial force, extends out from the outer casing 39, as shown in Figure 9.

The first stage in fitting the sensor arrangement 301 to the hot water cylinder assembly 31 is to drill a hole through the outer casing 39 and the rigid foam insulation jacket 29 (but not the tank wall 35) to create the fitment bore 27. The sensor arrangement 301 can then be located in an initial position within the fitment bore 27, as shown in Figure 10.

An axially directed securing force, in the proximal direction, is then applied to the distal end of the insert 311. In a first phase of application of the force the contact face 15 of the sensor 3 is brought into contact with the external surface of the tank wall 35. In a second phase of application of the securing force, the insert 311 begins to become compressed along the X-X axis, because it can no longer freely move axially in a proximal direction once the sensor 3 is abutting the tank wall 35 and the thrust surface 320 of the centring bead 310 has come into contact with the push-on lock washer 309. This axial compression of the insert 311 causes the bore 323 of the insert 311 to close up around the cable 305 and the body of the insert 311 to expand radially outwardly to close up the gap between the external surface of the insert 311 and the wall of the fitment bore 27. This is shown in Figure 11. In a compressed state the insert 311 has two portions which perform different purposes. The distal portion, insert anchoring portion 311a, has been compressed by the securing force and radially expanded and is in contact with the wall of the fitment bore 27. The insert anchoring portion 311a anchors the insert 11 to the wall of the fitment bore 27. The proximal portion, insert compressing portion 311b, has been compressed by the securing force and has transferred the compressive force to the sensor 303 and the push-on lock washer 309 to hold the sensor 303 in contact with the external surface of the tank wall 35. The insert compressing portion 311b cannot expand back to its pre-fitment state (which might result in the sensor 303 coming out of contact with the tank wall 35), because the combination of the conical shape of the insert 311 and the anchoring of the insert 311 to the rigid foam insulation jacket 29 does not allow that to happen. In pressing the insert 311 against the fitment bore 27 the cellular structure of the foam of the insert 311 mechanically engages with the rigid foam of the insulating jacket 29 such that when the securing force is no longer applied the insert 311 retains a sufficient level of elastic deformation to ensure that the sensor 303 is held against the tank wall 35. The final step is to locate the grommet 313 within the hole drilled in the casing 39. The grommet 313 prevents chafing of the cable 305 against the casing 39.

The sensor arrangement 301 can be removed from the hot water cylinder assembly 31, for example to enable replacement of the sensor 303 if it fails. The grommet 313 is removed from the casing 39 and the insert 311 can be removed, for example by using a pair of needle nosed pliers, to grip the insert 311 and extract it, or by applying a distally directed pulling force to the sensor cable 305 to extract the insert 311. The insert 311 will elastically deform during this removal step thus preventing any damage to the fitment bore 311.

Figure 12 shows an array of eight temperature sensors 3, 203, 303 fitted to a hot water cylinder assembly 31. A wiring loom 37 connects the temperature sensors 3, 203, 303 to a control system 7 which can collect the electrical signals from the temperature sensors 3, 203, 303 and process them to provide information about the temperature of the water within the water tank 33. The wiring loom 37 connects the temperature sensors 3, 203, 303 in parallel. This facilitates the determination of an average indication of the state of charge, i.e. the amount of hot water in the tank. It is also advantageous to utilise a parallel wiring arrangement for the temperature sensors 3, 203, 303 because if one sensor fails the effect on the others is minimised. The number of temperature sensors 3, 203, 303 is the same, irrespective of the size of the water tank 33. Therefore, the length of the wires in the wiring loom 37 is determined by the size of the largest tank for which it is envisaged that the system will be used. If the wiring loom 37 is used on a smaller tank there will be an amount of slack in the wiring loom 37.

The wiring loom 37 is provided for fitment in a form in which each set of components, as provided for each of the three embodiments, are threaded on to a sensor cable 5, 205, 305, such that they are free to move along the cable 5, 205, 305, relative to each other and to the temperature sensor 3, 203, 303 (but without changing their order along the axis X-X), to facilitate fitment to the hot water cylinder assembly 31.