Device for a hot water tank

Abstract

NOT VISIBLE DUE TO STATUS OF PATENT

Description

[0001] DEVICE FOR A HOT WATER TANK

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority from South African provisional patent application number 2023 / 1 1726 filed on 21 December 2023, which is incorporated by reference herein.

[0004] FIELD

[0005] This disclosure relates to water heating. More specifically, it relates to a device for a hot water tank which may be used to derive a condition of a sacrificial anode of the hot water tank.

[0006] BACKGROUND

[0007] Hot water cylinders or tanks, also called geysers in South Africa, may have an anode rod that screws into the tank and protrudes into the water. These anode rods may be made from magnesium or aluminium, and their purpose is to reduce corrosion of the tank wall which is usually made of steel with an inner lining that may be vitrified porcelain or other enamel. Corrosive substances in the water attack the anode rod first as the magnesium or aluminium attracts free ions in the water and corrodes the anode instead of the tank wall. These anodes are therefore termed sacrificial anodes, and they require regular replacement to effectively protect the hot water tank.

[0008] Deterioration of the sacrificial anode over time leads to a reduction in protection, especially when the inner lining has become damaged as may occur through repeated expansion and contraction of the tank, transportation and handling of the tank, or through defects or holes in the inner lining, thereby exposing the tank wall to free ions in the water, or to sulphate-reducing bacteria present in the water which can cause or accelerate corrosion of the tank.

[0009] A potential difference between the sacrificial anode and the tank wall is indicative of the degree of protection offered by the sacrificial anode - i.e., whether the sacrificial anode is degraded and needs to be replaced or not. The reason for reduction in the degree of protection offered by the sacrificial anode is due to depletion of the sacrificial anode, leading to a reduction in protective potential over time.

[0010] An existing method of determining a condition of a sacrificial anode is to temporarily remove an existing bi-metallic thermostat of a hot water tank from its copper thermostat pocket and insert a probe into the pocket, with another probe touching the tank wall. Since the thermostat pocket is electrically insulated from the tank wall, the measured potential difference between the two probes indicates the condition of the sacrificial anode.

[0011] Such measurement is a manual process which can only be undertaken by a technician who inspects the tank. As a result, the corrosion of the sacrificial anode may go unnoticed and unattended. Once the anode has sufficiently deteriorated, it offers little to no corrosion protection.

[0012] The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application.

[0013] SUMMARY

[0014] In accordance with an aspect of the disclosure there is provided a device for a hot water tank, comprising a housing with an elongate stem extending from the housing, wherein the stem is configured to fit within a pocket of the hot water tank, the device including: a first conductor coupled to or extending along the stem with the first conductor configured to make electrical contact with an inner surface of the pocket, a second conductor configured to be mounted in electrical contact with a tank wall of the hot water tank; and a measurement circuit connected to the first conductor and second conductor, wherein the measurement circuit is configured to measure a potential difference between the first conductor and the second conductor.

[0015] The pocket of the hot water tank may be a thermostat pocket, in which instance an existing thermostat may be provided or may be removed. Alternatively the pocket may be a sleeve, bore or additional pocket which extends into the interior of the hot water tank. At least a portion of the pocket may be formed of a conductive material.

[0016] The hot water tank may include an anode, and the second conductor may be configured to be mounted in electrical contact with a tank wall that is in electrical contact with the anode. The measured potential difference may indicate a condition of an anode of the hot water tank, which may be a sacrificial anode. A decrease in the potential difference over time may indicate that the sacrificial anode is degraded and needs to be replaced. The measurement circuit may be within the housing and the elongate stem may be a conductive tube extending from the housing. The housing may include a sealed compartment for protecting the measurement circuit from dust and moisture, and may be made from a rigid material such as injection-moulded plastic. The housing may be shaped to fit against an end wall of the hot water tank and may have a squat profile.

[0017] The first conductor may be coupled to a proximate end of the conductive tube. The conductive tube may then be configured to contact the inner surface of the pocket.

[0018] To ensure that the conductive tube contacts the inner surface of the pocket, the conductive tube may be angled relative to the housing such that when fully inserted into the pocket, a distal end of the conductive tube contacts the inner surface of the pocket at a position within an interior of the tank. An alternative means of ensuring contact between the conductive tube and the pocket is to fit a spring-loaded clip or ring to the conductive tube, preferably at or near a distal end thereof.

[0019] The second conductor may be configured to be attached to an earth stud of the hot water tank. Such attachment may be by means of using an existing screw or bolt of the earth stud to secure a free end of the second conductor to the earth stud.

[0020] The housing may include a processor which receives readings from the measurement circuit. The processor may be a microprocessor and may also be located within the housing. The processor may periodically sample the measurement circuit and record the measured potential difference readings. The readings may be recorded on a memory coupled to the processor. The processor may cooperate with an alert controller configured to provide an alert in response to a predefined potential difference threshold change determined from the readings.

[0021] The device may include a communication module which communicates the potential difference readings to a server. The server may then be operable to alert a user when the potential difference readings indicate that replacement of the anode is required.

[0022] In one embodiment, the device includes a temperature sensor located near a distal end of the stem, and a controller within the housing for selectively energising or de-energising a heating element or heating system of the hot water tank based on measured temperature. The device may thus also function as a smart thermostat which replaces an existing thermostat of the hot water tank. Another aspect of the disclosure extends to a thermostat device for a hot water tank, comprising a housing with an elongate stem extending from the housing, wherein the stem is configured to fit within a pocket of the hot water tank, the device including: a temperature sensor located near a distal end of the stem, and a controller within the housing for selectively energising or de-energising a heating element or heating system of the hot water tank based on temperature measurements from the temperature sensor; a first conductor coupled to or extending along the stem with the first conductor configured to make electrical contact with an inner surface of the pocket, a second conductor configured to be mounted in electrical contact with a tank wall of the hot water tank; and a measurement circuit connected to the first conductor and second conductor, the measurement circuit configured to measures a potential difference between the first conductor and the second conductor.

[0023] The thermostat device may include: a processor which receives readings from the measurement circuit and records the measured potential difference readings on a memory coupled to the processor; and an alert controller configured to provide an alert in response to a predefined potential difference threshold change determined from the readings. The housing may include a communication module which communicates the potential difference readings to a server.

[0024] Another aspect of the disclosure extends to a water heating system, comprising: a tank that includes a tank wall, a pocket extending into the tank and an anode; and a device mounted to the tank, the device including: a housing having an elongate stem extending from the housing that projects into the pocket; a first conductor coupled to or extending along the stem with the first conductor making electrical contact with an inner surface of the pocket, and a second conductor mounted in electrical contact with the tank wall; and a measurement circuit connected to the first conductor and second conductor, wherein the measurement circuit is configured to measure a potential difference between the first conductor and the second conductor, the potential difference indicating a condition of the anode.

[0025] The pocket of the hot water tank may be a thermostat pocket, in which instance an existing thermostat may be removed; alternatively the pocket may be a sleeve, bore or additional pocket which extends into the interior of the tank. The device may include any of the features described above.

[0026] A yet further aspect of the disclosure extends to a method of monitoring a condition of an anode of a hot water tank, comprising: removing an existing thermostat from a thermostat pocket of a hot water tank; fitting a device to the hot water tank, the device having a housing with an elongate stem extending from the housing, the stem fitting within the thermostat pocket, and the device having a first conductor coupled to or extending along the stem with the first conductor making electrical contact with an inner surface of the thermostat pocket; attaching a second conductor of the device in electrical contact with a tank wall of the hot water tank; by means of a measurement circuit of the device, periodically sampling the potential difference between the first conductor and the second conductor, where the measured potential difference indicates a condition of the anode.

[0027] The method may also include communicating the measured potential difference readings to a server.

[0028] The method may also include using measurements from only specific periods of the day to determine the anode potential. For example, a daily average anode potential may be calculated using measurements taken over periods of no heating and no water draws to improve accuracy and reduce the impact of short-term fluctuations due to non-equilibrium conditions in the tank.

[0029] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings.

[0030] BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In the drawings:

[0032] Figure 1 is a schematic view of a water heating system that includes a hot water tank and a device;

[0033] Figure 2 is a schematic diagram showing an electrical circuit resulting from the use of the device; and

[0034] Figure 3 is a diagram that shows one exemplary embodiment of the device. DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

[0035] Embodiments of the disclosure provide for a device for a hot water tank, a water heating system, and a method for monitoring a condition of an anode of a hot water tank. An anode (usually formed of magnesium or aluminium) is provided in a hot water tank to generate a negative potential to attract free ions in the water of the tank to the anode to corrode the anode instead of a surface of the tank. The anode may be a single anode or may be split into multiple portions.

[0036] The described device for a hot water tank is configured to monitor a condition of an anode of the hot water tank. The device may be a stand-alone device or may be incorporated into a thermostat device of the hot water tank. An indication of an anode condition may be obtained by measuring the potential difference of the water in the tank between a point inside the tank and the tank wall. The anode condition relates to a degree of depletion of the anode and therefore the protective potential provided by the anode. Measuring the potential difference in the water of the tank provides a measurement of the protective potential of the anode. The protective potential varies across the tank, but the potential between a point inside the tank and the tank wall is reasonably representative of the overall protective potential of the anode.

[0037] The described device has two conductors for measuring the potential difference in the tank water. A first conductor is configured to be disposed in a conductive pocket or inlet that positions it inside the volume of the tank with the pocket insulated from the wall of the tank. The second conductor is positioned in electrical contact with the tank wall.

[0038] In one example, a device includes a housing with an elongate stem or rod extending from the housing. The stem may be configured to fit within a pocket, bore or sleeve of a hot water cylinder or tank. A first conductor may be coupled to or may extend along the stem, with the first conductor arranged to make electrical contact with an inner surface of the pocket, either directly or via the stem. A second conductor may be configured to be mounted or attached in electrical contact with a tank wall of the hot water tank. Such mounting or attachment may be by means of bolting or securing an end of the second conductor to a structure in contact with the tank wall, such as an earth stud provided on the tank. The pocket is insulated from the tank wall to which the second conductor is in electrical contact.

[0039] The device may include a measurement circuit connected to the first conductor and the second conductor, the measurement circuit being operable to measure a potential difference between the first conductor and the second conductor. The measurement circuit is configured not to impact the lifetime of the anode by having a high impedance in the measurement path. The measurement circuit may draw less than 5 micro Amp of galvanic current.

[0040] A change in the measured potential difference may indicate a change in a condition of the anode. The measurement circuit may be configured to continuously monitor the potential difference between the conductors and therefore the condition of the anode. A processor may be provided in communication with the measurement circuit and may provide an output of an alert when the potential difference indicates that the anode needs replacement. The alert may be within a threshold of an effective operation of the anode allowing for pre-emptive replacement of the anode.

[0041] Figure 1 is a schematic view of an example embodiment of a water heating system (10). The system (10) includes a tank (12) that has a tank wall (14). The tank (12) may be a hot water cylinder or tank, also termed a geyser in South Africa. Such tanks may be of different sizes and configurations, and the tank wall (14) may be steel and may have an inner protective lining which may be an enamel or other suitable coating intended to protect the tank wall (14). The tank (12) may also include at least one pocket (16). The pocket (16) may have at least a portion formed of conductive material. The pocket (16) may be a thermostat pocket, which may be made of copper or other suitably conductive material, or may simply be coated with copper or other material such as nickel or chrome. Alternatively, the pocket (16) may be an additional, unused pocket, provided in the tank, or another structure such as a sleeve or bore extending into an interior of the tank.

[0042] The tank (12) may also include an anode (18), which may be a sacrificial anode. The anode (18) may be a rod made from magnesium or aluminium and may extend into the interior of the tank (12). It may be up to 1 meter long or even longer in some applications, and may have a reinforced core to give it rigidity. The anode (18) is generally mounted to the same side wall of the tank as the pocket (16). The anode (18) may reduce corrosion of the tank wall (14) as it may attract free ions in the water and therefore corrode itself instead of the tank wall (14) corroding, which can happen if cracks open in the inner protective lining of the tank.

[0043] The water heating system (10) may also include a device (20) configured to be mounted to the tank (12). The device (20) may be capable of measuring a potential difference in the water in the tank between the pocket (16) and a surface of the tank wall (14) that may be near the anode (18) and monitoring the change in such potential difference over time. A decrease in the measured potential difference may indicate a deterioration in a condition of the anode (18), e.g. due to corrosion of the anode, and thereby indicating that the anode may require replacement. The device (20) may include a housing (22) with an elongate stem (24) extending from the housing (22). The stem (24) may be configured to fit within the pocket (16) of the tank (12). The device (20) may include a first conductor (26), e.g. a first sensor wire, and a second conductor (28), e.g. a second sensor wire. The first conductor (26) may be configured to be coupled to or extend along the stem (24) and make electrical contact with the pocket (16) at a distal end of the pocket (16). The second conductor (28) may be configured to be mounted in electrical contact with the tank wall (14). The device (20) may include a measurement circuit (30) connected to the first conductor (26) and connected to the second conductor (28). The measurement circuit (30) may be arranged to measure a potential difference between the first conductor (26) and the second conductor (28).

[0044] The pocket (16) may be electrically insulated from the tank wall (14), for example by means of a thermoplastic or other insulation structure (32). The pocket (16) may be made from an electrically conductive material, such as copper. Therefore, by making electrical contact with the pocket (16), the first conductor is in electrical contact with the content of the tank (12), typically being water, while not being in contact with the tank wall (14).

[0045] The anode (18) may be mounted in electrical contact with the tank wall (14), for example by means of a wire (34) or simply by being attached to a mounting structure that is in contact with the tank wall (14). Therefore, by making electrical contact with the tank wall (14), the second conductor (28) is in electrical contact with the anode (18).

[0046] Because the anode (18) attracts free ions, a potential difference exists between the anode (18) and the copper pocket (16). This potential difference depends on the tank structure, position of the anode (18) and pocket (16), as well as the temperature of the water, and may start at around 1 .2 V for magnesium anodes in new tanks. A change in this potential difference over time, and in particular a decrease in this potential difference, may indicate that the anode is no longer protecting the tank from corrosion and is in need of replacement. For example, a decrease in this voltage to about 0.6 to 0.8V may be indicative of a depleted magnesium anode in certain water tank configurations. A voltage threshold decrease may be defined based on the tank configuration.

[0047] The first conductor (26) may make electrical contact with the pocket (16) in several ways. In one example, the stem (24) is a copper tube. The first conductor (26) may be connected to a proximate end (36) of the copper tube (24). The copper tube (24) may then be configured to contact an inner surface of the pocket (24). To ensure that the copper tube (24) contacts the inner surface of the pocket (16), the copper tube (24) may be angled relative to the housing (22) such that when fully inserted into the pocket, the copper tube contacts the inner surface of the pocket. An alternative means of ensuring contact between the copper tube and the pocket is to fit a spring-loaded clip or ring to the copper tube, preferably at or near a distal end (38) thereof.

[0048] The second conductor (28) may be mounted in electrical contact with the tank wall (14) by attaching it to an earth stud (39) of the tank (12). Such attachment may be by means of using an existing screw or bolt of the earth stud to secure a free end of the second conductor (28) to the earth stud (39).

[0049] The measurement circuit (30) may be within the housing (22), and the device (20) may also include a processor (40) within the housing which receives readings from the measurement circuit (30). The processor (40) may be a microprocessor and may also be located within the housing. The processor (40) may periodically sample the measurement circuit and record the measured potential difference readings. The readings may be recorded on a memory coupled to the processor.

[0050] The processor (40) may include an output for display or notification of the readings. The processor (40) may include an output of an alert when the potential difference indicates that the anode needs replacement. The alert may be within a threshold of an effective operation of the anode allowing for pre-emptive replacement of the anode.

[0051] The device (20) may also include a communication module (42) within the housing. The communication module (42) may communicate the output of potential difference readings to a remote server, for example a cloud-based computing system via an intermediate telecommunication system. The remote server may then be operable to inform, display to or alert a user when the potential difference readings indicate that replacement of the anode (18) is required.

[0052] Figure 2 is a schematic diagram showing an electrical circuit resulting from an example embodiment of use of the device (20). The measurement circuit (30) is connected by means of the first conductor (26) to the stem (24) which in turn is connected to the pocket (16). In one example, the stem (24) may be a copper tube and the pocket (16) may be formed of copper. The measurement circuit is also connected by means of the second conductor (28) to the earth stud (39), which is attached to the tank wall (14) of the tank (12), which is attached to the anode (18). By using the first and second conductors, the measurement circuit is therefore measuring a potential difference between the pocket (6) and the anode (18) within the tank water (14). The measurement circuit (30) is designed to not adversely impact the lifetime of the anode. High impedance is therefore needed in the illustrated measurement paths so that a low galvanic current flows, for example less than 5 micro amperes. It is also important that the pocket remains isolated from the tank wall, so the device (20) must not (though other parts or structures) bypass that isolation.

[0053] The measured voltage may be affected by parameters such as the coating of the pocket (e.g. copper, chrome or nickel), the relative position of the pocket and anode and the size of the tank. The device (20) may therefore be configured with information on the model and size of tank and may retrieve a set of parameters from memory so that the measured potential difference can correctly be correlated to tank-specific parameters.

[0054] Figure 3 illustrates one exemplary embodiment of the device (20). The housing (22) of the device may be a sealed compartment for protecting the measurement circuit (30), processor (40) and communication module (42) from ingress of dust and moisture. The housing (22) may be made from a rigid material such as injection-moulded plastic. The housing (22) may have a squat profile and be shaped to fit against an end wall (44) of the tank (12).

[0055] In this illustration, the device (20) may be in the form of a thermostat and may include a temperature sensor (46) within the stem (24), in this case located near the distal end (38) of the stem (24). The device (20) may include a controller within the housing for selectively energising or de-energising a heating element or heating system (not shown) of the hot water tank based on temperature readings received from the temperature sensor (46). The device (20) may therefore perform the additional function of being a smart thermostat of the hot water tank (12) as well as the anode condition monitor functionality. The device (20) may accordingly be configured to replace an existing bi-metallic thermostat of the tank (12).

[0056] By using the described device (20), the condition of an anode of a hot water tank can be monitored. The method includes: removing an existing thermostat from a thermostat pocket (16) of a hot water tank (12); fitting a device (20) to the hot water tank (12), the device (20) having a housing (22) with an elongate stem (24) extending from the housing (22), the stem (24) fitting within the thermostat pocket (16), and the device (20) having a first conductor (26) coupled to or extending along the stem (24) with the first conductor (26) making electrical contact with an inner surface of the thermostat pocket (16); attaching a second conductor (28) of the device (20) in electrical contact with a tank wall (14) of the hot water tank (12); by means of a measurement circuit (30) of the device, periodically sampling the potential difference between the first conductor (26) and the second conductor (28), where the measured potential difference indicates a condition of the anode (18).

[0057] The method may also include communicating the measured potential difference readings to a server. The method may also include using measurements from only specific periods of the day to determine the anode potential. For example, a daily average anode potential may be calculated using measurements taken over periods of no heating and no water draws to improve accuracy and reduce the impact of short-term fluctuations due to non-equilibrium conditions in the tank.

[0058] By utilizing an existing pocket of a hot water tank and providing a device which is able to periodically and automatically sample a potential difference which indicates a condition of a tank anode, the need for a technician to inspect an anode of a tank may be avoided, and early notice of a deteriorating anode may be obtained to enable suitable action to be undertaken. By integrating the device into a smart thermostat, the measurements can be made without any additional sensors or equipment being required, as the full measurement capability is included in the smart thermostat which has remote communication capabilities. The technology therefore enables a smart thermostat to also function as an anode condition monitoring system. In addition, through monitoring the rate of anode potential reduction over time, the technology may enable a prediction to be made as to when the anode will be depleted, allowing for preventative maintenance to be scheduled well in advance.

[0059] The foregoing description has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the technology to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure.

[0060] The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the present disclosure be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the present disclosure is intended to be illustrative, but not limiting, of the scope of any accompanying claims. Finally, throughout the specification and any accompanying claims, unless the context requires otherwise, the word ‘comprise’ or variations such as ‘comprises’ or ‘comprising’ will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

CLAIMS:1 . A device (20) for a hot water tank (12), comprising a housing (22) with an elongate stem (24) extending from the housing, wherein the stem is configured to fit within a pocket (16) of the hot water tank, the device including: a first conductor (26) coupled to or extending along the stem with the first conductor configured to make electrical contact with an inner surface of the pocket, a second conductor (28) configured to be mounted in electrical contact with a tank wall (14) of the hot water tank; and a measurement circuit (30) connected to the first conductor and second conductor, wherein the measurement circuit is configured to measure a potential difference between the first conductor and the second conductor.

2. The device as claimed in claim 1 , wherein the pocket is a thermostat pocket in which a thermostat is provided or from which an existing thermostat has been removed.

3. The device as claimed in claim 1 or claim 2, wherein the hot water tank includes an anode (18) and the second conductor (28) is configured to be mounted in electrical contact with a tank wall that is in electrical contact with the anode (18), and wherein the measured potential difference indicates a condition of the anode (18).

4. The device as claimed in claim 3, wherein a decrease in the measured potential difference over time indicates that the anode is degraded and needs to be replaced.

5. The device as claimed in any one of the preceding claims, wherein the housing includes a sealed compartment for protecting the measurement circuit from dust and moisture and wherein the housing is made from a rigid material.

6. The device as claimed in any one of the preceding claims, wherein the housing has a squat profile and is shaped to fit against an end wall (44) of the hot water tank.

7. The device as claimed in any one of the preceding claims, wherein the elongate stem is a conductive tube extending from the housing and the first conductor is coupled to a proximate end (36) of the conductive tube.

8. The device as claimed in claim 7, wherein a distal end of the conductive tube is configured to contact an inner surface of the pocket at a position within an interior of the tank.

9. The device as claimed in claim 8, wherein the conductive tube is angled relative to the housing such that when fully inserted into the pocket, the conductive tube contacts the inner surface of the pocket.

10. The device as claimed in claim 7 or claim 8, wherein the conductive tube includes a spring- loaded clip or ring configured to contact the inner surface of the pocket.1 1 . The device as claimed in any one of the preceding claims, wherein the second conductor is configured to be attached to an earth stud (39) of the hot water tank.

12. The device as claimed in any one of the preceding claims, wherein the housing includes a processor (40) which receives readings from the measurement circuit and records the measured potential difference readings on a memory coupled to the processor.

13. The device as claimed in claim 12, wherein the housing includes a communication module (42) which communicates the potential difference readings to a server.

14. The device as claimed in any one of the preceding claims, including a temperature sensor (46) located near a distal end (38) of the stem, and a controller within the housing for selectively energising or de-energising a heating element or heating system of the hot water tank based on temperature measurements from the temperature sensor.

15. A thermostat device for a hot water tank (12), comprising a housing (22) with an elongate stem extending (24) from the housing, wherein the stem is configured to fit within a pocket (16) of the hot water tank, the device including: a temperature sensor (46) located near a distal end (38) of the stem, and a controller within the housing for selectively energising or de-energising a heating element or heating system of the hot water tank based on temperature measurements from the temperature sensor; a first conductor (26) coupled to or extending along the stem with the first conductor configured to make electrical contact with an inner surface of the pocket, a second conductor (28) configured to be mounted in electrical contact with a tank wall (14) of the hot water tank; and a measurement circuit (30) connected to the first conductor and second conductor, the measurement circuit configured to measures a potential difference between the first conductor and the second conductor.

16. The thermostat device as claimed in claim 15, including: a processor (40) which receives readings from the measurement circuit and records the measured potential difference readings on a memory coupled to the processor; and an alert controller configured to provide an alert in response to a predefined potential difference threshold change determined from the readings.

17. The thermostat device as claimed in claim 15 or claim 16, wherein the housing includes a communication module (42) which communicates the potential difference readings to a server.

18. A water heating system (10), comprising: a tank (12) that includes a tank wall (14), a pocket (16) extending into the tank and an anode (18); and a device (20) mounted to the tank, the device including: a housing (22) having an elongate stem (24) extending from the housing that projects into the pocket; a first conductor (26) coupled to or extending along the stem with the first conductor making electrical contact with an inner surface of the pocket; a second conductor (28) mounted in electrical contact with the tank wall; and a measurement circuit (30) connected to the first conductor and second conductor, wherein the measurement circuit is configured to measure a potential difference between the first conductor and the second conductor, the potential difference indicating a condition of the anode.

19. The water heating system as claimed in claim 18, wherein the pocket of the hot water tank is a thermostat pocket from which an existing thermostat has been removed, or is a sleeve, bore or additional pocket which extends into an interior of the hot water tank.

20. A method of monitoring a condition of an anode (18) of a hot water tank (12), comprising: removing an existing thermostat from a thermostat pocket (16) of the hot water tank; fitting a device (20) to the hot water tank, the device having a housing (22) with an elongate stem (24) extending from the housing, the stem fitting within the thermostat pocket, and the device having a first conductor (26) coupled to or extending along the stem with the first conductor making electrical contact with an inner surface of the thermostat pocket; attaching a second conductor (28) of the device in electrical contact with a tank wall of the hot water tank;by means of a measurement circuit (30) of the device, periodically sampling the potential difference between the first conductor and the second conductor, where the measured potential difference indicates a condition of the anode.

21. The method as claimed in claim 20, including communicating the measured potential difference readings to a remote server.

22. The method as claimed in claim 20 or claim 21 , including determining a condition of the anode using measurements from periods of no heating of the hot water tank and no water draws.