The invention relates in general to control of temperature controlled heating processes, in particular heating boilers. More specifically, the invention relates to a boiler control unit which includes a delayed cycle controller.

Heating boilers (oil or gas) for heating the rooms of a building and/or for providing tap hot water are usually controlled by a thermal relay which provides an on/off temperature control. Such boilers are typically dimensioned in such a way that they are able to manage conditions in which an extremely high heating demand exists, i.e. during the coldest winter days. This means that the capacity of the heating boiler is utilised to the greatest extent during the cold periods of the year. During the remaining parts of the year, the boilers are over-dimensioned, and consequently, the overall efficiency is not optimal.

A solution to the above problem is presented in WO94/02787, which discloses a delayed cycle control unit for a heating boiler equipped with an on- off controllable burner. The use of such a control unit results in an improved overall energy efficiency, particularly in periods with low loads, i.e. during moderate and warm seasons. The boiler is provided with a thermal relay, which provides a temperature responsive signal which is switched on when the temperature in the boiler underpasses a lower temperature level and switched off when the temperature in the boiler exceeds a higher temperature level.

When the high temperature limit is reached, the burner is switched off, as also would be the case if the thermal relay controlled the burner directly. However, when the low temperature limit is reached, the burner is not switched on immediately, as would be the case if the thermal relay controlled the burner directly. Instead, the control unit is arranged to measure the cooling time of the boiler, by measuring the time that has elapsed between the on-to- off transition and the off-to-on transition of the signal provided by the thermal relay. The control unit is further arranged to add a certain percentage to this cooling time, resulting in a time delay, and to switch on the burner when this time delay has elapsed.

The system interfaces with an external computer so that parameters such as the additional cooling time delay percentage may be set. This system provides an improved energy efficiency. However, the additional cooling time delay percentage is a static quantity, which must be pre-set by an operator.

An improvement is disclosed in WO2006/036064, in which the delay is dynamically adjusted based on changes in the temperature of the boiler outlet. Essentially, if the temperature drop during the extended cooling period is small (based on a measure which is linked to the temperature drop during the normal cycling function), the extended cooling period is increased in duration (by increasing the delay percentage value). If the temperature drop during the extended cooling period is large (again based on a measure which is linked to the temperature drop during the normal cycling function), the extended cooling period is reduced in duration (by decreasing the delay percentage value).

The known device has a test port. Periodically (such as every 50 cycles) the unit generates a report by providing a measurement of the burning period duration and the cooling period duration, with the delayed cycle controller enabled then disabled.

This information can be downloaded from a test port to a remote unit. The reports can then be used to provide an estimate of the savings in energy which are being achieved.

One problem with the known system is that the energy savings estimates are not very accurate. The test is a short term automatic test, and the results will depend on the load on the boiler at any time, so that it cannot give an accurate assessment of the overall energy savings. Another problem is that test reports have to be extracted from the controller on site. The invention is defined by the claims.

According to the invention, there is provided a boiler control system for controlling a heating device in a boiler, comprising: a delayed cycle controller for activating and deactivating said heating device based on an upper temperature threshold and a lower temperature threshold; and

an interface system comprising:

a command unit for commanding the delayed cycle controller to be enabled or disabled and to instruct performance of an efficiency test;

a pulse counting unit for counting units of energy supplied to the boiler; and

a wireless transmitter for transmitting the efficiency test results to a user including energy supply information.

This boiler control system enables remote wireless accessing of test data. In addition, by providing pulse counting, the energy supplied (e.g. gas volume) can be measured, and this can enable much more accurate assessment of energy savings being made by the delayed cycle control.

The wireless transmitter can be shared between multiple boilers. In this way, a set of boilers each communicate with a single wireless transmitter which enables dialogue with the user. The multiple boilers may be part of a large building, such as a hospital or school, and by providing pulse counting at the individual boiler level, or at the level of a sub-set of boilers sharing a common sub-meter, per-boiler gas usage can be obtained.

Thus, this aspect of the invention provides a system from controlling the heating devices of a set of boilers, comprising a boiler control system for each boiler and a wireless transmitter for transmitting efficiency test data in respect of each of the boilers to a user, wherein each boiler control system comprises:

a delayed cycle controller for activating and deactivating the boiler heating device based on an upper temperature threshold and a lower temperature threshold; and

an interface system, comprising:

a command unit for commanding the delayed cycle controller to be enabled or disabled and to instruct performance of an efficiency test; and a pulse counting unit for counting units of energy supplied to the boiler.

Each boiler or sub-set of boilers in this system preferably has a sub- meter for the energy supply so that the pulse counting can give an indication of the energy supply to each boiler or sub-set of boilers.

When multiple boilers share one meter or sub-meter, a test procedure can be carried out in turn, so that the pulse counting can be used to determine the energy savings of an individual boiler.

The interface system can comprises an RS232 to R485 converter. This means the system can be retrofitted to existing installations having an RS232 output test port, to enable them to be converted to wireless RS485 systems without replacing the existing delayed cycle controller. This enables a low cost upgrade to existing installations, to enable both wireless remote system testing and reporting, as well as improved energy efficiency statistics to be obtained.

The interface system can comprise a temperature sensor. This enables the test results to be calibrated with respect to the ambient temperature (known as "degree day compensation").

It is known to take account of temperature in efficiency savings calculations, but this involves use of a published grid of temperature statistics. These may give figures only every 50km for example, and the use of a temperature sensor, preferably mounted with the wireless transmitter, enables further accuracy improvements in the energy saving calculations.

The wireless transmitter preferably comprises a GPRS transmitter. The wireless transmitter can further comprise a receiver, for receiving wireless commands for controlling the test procedures. In this way, a user or the system installer can remotely interrogate the system, and instruct the desired test procedures and receive the test results. Boiler configuration settings can also be amended using the wireless interface.

In one example, a temperature sensor is provided for measuring a boiler temperature and the system has an interrupt unit for interrupting a heating device enable signal thereby to implement the delayed cycle control of the delayed cycle controller. The interrupt unit can comprise a relay switch.

This arrangement provides delayed cycle control by interrupting an enable signal. This means that the normal thermostatic boiler control does not need to be altered, so that the system can be used with electronic boilers without generating errors. In particular, the heating device enable signal is one which takes priority of the internal boiler thermostatic control of the burner. The heating device enable signal can comprise a building management system burner enable signal.

An example of the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 shows a known boiler control unit;

Figure 2 shows a timing diagram to explain the operation of the known unit as well as the operation of the an improved control unit proposed by the applicant;

Figure 3 shows the unit of Figure 1 modified to function in accordance with the invention;

Figure 4 shows an arrangement with multiple boilers;

Figure 5 shows a boiler control unit which can be adapted in accordance with the invention in schematic form;

Figure 6 shows an example of boiler control approach which can be used in more detail;

Figure 7 shows timing diagrams to explain the method of the approach of Figure 6 compared to the earlier known methods; and

Figure 8 shows timing further diagrams.

The invention provides a boiler control system which uses a delayed cycle controller in which an interface system is used to enable or disable the delayed cycle control and count units of energy supplied to the boiler. A wireless transmitter is used for transmitting the test data to a user. This system enables remote wireless collection of data, and enables improved energy efficiency calculations to be obtained.

Figure 1 shows a known heating boiler 1 controlled by a control unit 10.

The boiler 1 comprises a water tank 3, an inlet conduit 4, an outlet conduit 5, and a burner 2 controlled in an on-off manner by a delayed cycle controller 1 1 in the control unit 10. A thermal relay 6 provides a temperature responsive signal 7 which is switched on when the temperature in the boiler underpasses a lower temperature level. The signal 7 is further switched off when the temperature in the boiler exceeds a higher temperature level.

The delayed cycle controller 1 1 is further arranged to produce a control signal 8 for input to the burner 2, in order to switch the burner 2 on and off as a function of the thermal relay signal and the time. More specifically, the control signal is switched off immediately when the thermal relay signal 7 is switched off, and the control signal is switched on at a delayed point of time after the thermal relay signal 7 is switched on.

In this known system, the delay is calculated by the controller 1 1 as a certain percentage of the boiler's cooling time, i.e. the time elapsed from the on-off transition to the off- on transition of the signal 7 provided by the thermal relay 6. The control unit 10 is further adapted to communicate with an external computer 13.

A temperature sensor 15 is arranged to measure the temperature of the tap hot water in the outlet 5 from the tank 3.

The basic controller 1 1 with no delayed cycle control is arranged to compare the temperature measured with the temperature sensor 15 with a preset lower temperature level, and to start the burner if the measured temperature becomes lower than the lower temperature level.

The known delayed cycle controller adds a time period after the time when the temperature becomes lower than the lower temperature level. In a first known example, a cooling time delay percentage is stored as a fixed value, so that the cooling time is extended by a given fraction. In a second known example, the percentage value is dynamically controlled, and an algorithm for this purpose is shown as 12. Figure 2 is a graph illustrating the boiler temperature as a function of time, in order to illustrate the operation of the delayed cycle controller.

At time 0 the burner is fired.

At time τ1 the signal 7 provided by the thermal relay 6 is switched off, and the controller 1 1 switches off the burner 2. The cooling time of the thermal relay is measured by the controller 1 1 as the period τ2- τ1.

At τ2, the signal 7 provided by the thermal relay 6 is switched on. Without delayed control, the burner would then be turned on.

However, the delayed cycle controller 1 1 does not start the burner immediately, at time τ2, but delays the start until the time τ3. The delay τ3- τ2 is calculated by the controller 1 1 as the stored delay percentage of the measured cooling time τ2- τ1.

As shown, the extended cooling time gives rise to cooling beyond the original lower threshold temperature of T2 to temperature T3.

By way of example, the duration of time 0 - τ1 may be of the order of 5 minutes, and the duration of time τ1 to τ2 may be of the order of 10 minutes.

The known system makes use of the existing temperature sensor 15 which forms part of the original boiler equipment. However, for some boiler types, for example with electronic control systems, it is not possible to use this signal in the manner previously proposed, since it can result in a shutdown of the boiler based on a mismatch between the burner signal generated by the thermostatic control and the actual burner performance.

The applicant has proposed a delayed cycle control which does not require alteration to any of the original boiler equipment. This means that the electronic control system can be made to be essentially unaware of the presence of the system.

In commercial boiler systems, a building management system provides an enable signal for control of the boiler, which essentially functions as an override signal. The building management system ("BMS") is used to control systems within a building which contribute to the building's energy usage, and this can include heating, lighting and ventilation control. The BMS can also provide access control and other security systems such as closed-circuit television (CCTV) and motion detectors. Fire alarm systems and elevators are also sometimes linked to a BMS, for monitoring.

The heating control provided by BMS is typically implemented as an enable signal provided to the boiler. This enable signal is a command sent to the burner instructing it to fire in accordance with the thermostatic control, and a non-enable signal overrides the thermostatic control. By withholding the enable signal, the BMS can prevent burner operation when it detects that such burner operation is not needed. The enable signal is thus a signal external to the boiler which takes priority over the internal thermostatic control of the heating device in the boiler.

The applicant has proposed making use of this enable signal as a means for providing delayed cycle control. In particular, the system takes control of the burner "enable" signal, which is provided to the boiler from the building management system (BMS).

Electronic boilers are designed to follow the instructions of the BMS in preference to the thermostat cycles. Thus, by generating a BMS signal to turn off the burner or delay the burner turning on, the system can function with all types of boiler without generating errors.

The proposed system is based on a microprocessor controlled self- setting thermostat for boilers. The system overrides the boiler internal thermostat and controls the boiler burning cycles without interfering with any of the boiler's internal electrical or mechanical equipment.

This invention can be applied to both of these delayed cycle control approaches, as well as others.

Figure 3 shows the system of Figure 1 modified to provide the improvement of one example of the invention.

The same references are used as in Figure 1 , and a description of the repeated components is not provided.

An example of the invention will be explained based on an upgrade to an existing system. The upgrade takes the form of an addition remote terminal unit 30 which is connected to the delayed cycle controller 1 1 . It can for example connect to the test data extraction port to which the computer 13 was connected in the system of Figure 1 .

The unit 30 includes a command unit which can command the delayed cycle controller to be enabled or disabled. Thus, instead of a fixed periodic test, the invention enables any desired test sequence to be selected. For example, a test may be made at a given time each day, or a number of times each day, over a desired length of time. As in the prior art system, the testing involves comparing the boiler performance with and without the delayed cycle controller being active.

Instead of measuring time periods, the invention enables more accurate measurement of energy usage, by using a pulse counting unit 32 for counting units of energy supplied to the boiler. These pulses are generated by the meter, for example gas meter, for example with each pulse representing 0.1 cubic meters of gas. A signal line 33 is provided from the meter to the unit 30 for this purpose.

The system further comprises a wireless transmitter 36 for transmitting the test data to a user, for example using GPRS communications. This can be mounted in the consumer unit.

This boiler control system enables remote wireless accessing of test data. In addition, by providing pulse counting, the energy supplied (e.g. gas volume) can be measured, and this can enable much more accurate assessment of energy savings being made by the delayed cycle control.

In the example shown, where the unit is a retrofit to an existing delayed cycle controller, the unit can convert between the protocol of the test port, and the current protocol to enable communication with the wireless transmitter 36.

In one example, the unit 30 comprises an RS232 to R485 converter 34. This is the "Modbus" protocol. The transmitter 36 functions as the Modbus master unit and the remote terminal unit 30 is the slave device. The transmitter thus communicates (with a wired connection) with the unit 30 using the Modbus system and also has a GPRS transmitter for enabling wireless access and control. The system has a temperature sensor for detecting the ambient temperature. This can be mounted with the wireless transmitter away from the heat generated by the boiler, or else there can be one near each remote terminal unit.

The transmitter 36 can communicate with multiple slave devices.

Figure 4 shows an installation with three boilers B1 , B2 and B3. Each has its own delayed cycle controller including the remote terminal unit of the invention, shown as RTU1 , RTU2 and RTU3. Each RTU has its own ID and they connect to a common communications bus and are polled by the master unit forming part of the transmitter.

There is a master meter M1 and two sub meters SM1 , SM2. The first sub meter SM1 feeds gas (or oil) to the first two boilers B1 , B2, and a pulse count signal is sent from the sub meter SM1 to the associated remote units RTU1 , RTU2. The thick lines represent fuel supply and the thin lines represent electrical signals.

A second sub meter SM2 supplies the third boiler B3.

By using the pulse count signal, the efficiency of each boiler can be determined. When one sub meter supplies a single boiler, such as SM2, the pulse count relates to the energy usage of that boiler. When multiple boilers are supplied by one sub meter, such as B1 and B2, they can be operated in sequence during a testing cycle, to evaluate the individual energy savings made by the respective delayed cycle control units.

The remote terminal unit has input/output terminals for the RS232 signals, and input/output terminals for the RS485 signals, including level translation if required. There is a pulse count input and a temperature sensor input. The main component of the remote terminal unit is a microcontroller and its associated memory. An interface can also be provided for local wired communication with the unit, for example a Mini USB port.

As mentioned above, the invention can be applied to a standard delayed cycle controller. However, a variation proposed (but not yet published) by the applicant will also be explained. Figure 5 shows an example of this alternative system in schematic form.

The system 20 is independent of the boiler 1 and does not rely on signals from any internal boiler components. Instead, a flow temperature sensor 22 is part of the system. A further temperature sensor is provided on the return pipe. This can be used for example to ensure that if the water drops below a minimum temperature, the boiler can be instructed to fire immediately.

The boiler is controlled by a building management system 24 which provides a burner enable signal 26.

The proposed system overrides this, and this is represented schematically by the switch 28 which allows the burner control signal output by the system 20 to replace the BMS enable signal. The switch 28 may for example be implemented as contact relays.

The system needs an initial calibration. In particular, the system needs to be able to switch off the burner at the end of the burner cycle, instead of the boiler's internal thermostatic control. To enable this, when the system is fitted, it performs a monitoring function, during which the maximum and minimum temperatures provided by the normal boiler thermostatic control (i.e. T1 and T2 in Figure 2) are monitored. At the limit, only one burn cycle is needed for this monitoring, but two or three cycles may be followed as the initial calibration.

This initial calibration typically takes place when the boiler starts from cold (or with a water temperature below 30 degrees).

The system monitors the boiler's outgoing water temperature using its own thermistor which is piggybacked next to the internal boiler thermistor. It also monitors the return water temperature to the boiler.

In a first possible implementation, to enable the burn cycle to be ended at the same temperature (T1 in Figure 2), the thermostat setting of the boiler is increased by the installer after the initial calibration, so that the system then takes charge of ending the burner cycles. An alternative second implementation is for the system temperatures to chosen a small step below the monitored boiler settings.

By using the BMS "enable" signal, the system also takes charge of the timing of starting the burner cycles, as described below.

For the first implementation, to fit the system, the boiler's internal thermostat settings should can be raised by a fixed amount after the initial calibration, such as 3°C (for both the upper and lower switching thresholds), to enable the compensation system to be implemented.

The maximum temperature as implemented by the compensation system is set this same 3°C lower than the new boiler internal setting, so that the original maximum temperature setting is preserved. In this way, at the desired maximum temperature, the control of the switching off of the boiler can be implemented by the system of the invention instead of by the internal boiler control.

As mentioned above, delayed cycle controllers are known. The enhanced control approach can be applied to a system using a known delayed cycle controller, by providing additional components which take control of the BMS enable signal. Instead, the system can be implemented as a single self-contained unit.

Figure 6 shows how the system can be implemented in a way which makes use of an existing delayed cycle controller 40. This controller is associated with a temperature sensor 41 at the boiler output.

The BMS 24 provides its enable signal 26. This is interrupted by a zero contact relay 42. The enable signal is a low voltage signal, whereas the relay is controlled by a mains signal. The mains lines are shown as 44 between the boiler 1 , the controller 40 and also the sensor unit 46 which forms part of the added components.

The sensor unit 46 carries out the monitoring during the initial calibration described above. It is linked to a temperature sensor 48 at the boiler output.

The switch remains closed during the calibration so that the enable signal is not interrupted, and the boiler monitoring takes place. After the initial calibration, the sensor 46 provides control of the enable signal, thereby controlling when burning stops (because the boiler thermostat temperature has not yet been reached) and also controls when the burning starts again (because the raised boiler lower thermostat setting will have been passed).

The known use of the controller 40 would provide an interrupt signal to the burner of the boiler. In the arrangement of Figure 6, this burner interrupt signal is no longer coupled to the boiler. Instead, it is used to control the passage of the BMS enable signal to the boiler.

This arrangement essentially has two switches in series; the switch of the controller 40 and the switch of the sensor 46. During the initial calibration, the sensor 46 causes the normal internal boiler function to be followed, because the sensor 46 prevents any interruption of the enable signal. It is open so that the relay switch is not activated to open the relay switch (which is normally closed).

During the subsequent control, the sensor 46 allows the output of the controller 40 to be used to control the relay 42 and thereby implement the delayed cooling cycle.

In an integrated system, there is of course no need for separate switches, and the full functionality can be integrated into a single unit.

This provides a new approach to the way of controlling the extended cooling cycle. As explained above, the known method involves setting a target time duration for the extended cooling cycle.

This proposed system provides an approach based on temperature settings. This provides a more stable approach, which is less prone to instable variations. The dynamic control of the boiler burn and cool cycles is made simpler, and in particular requires no measuring of time delays. Furthermore, by using temperature measurement as the control parameter, it can be ensured that desired temperature levels are not exceeded, for example a minimum hot water temperature (which may be set of hygiene reasons).

This invention, i.e. the RTU for pulse counting and wireless data transmission, can be applied to the delayed cycle controller 40 of Figure 6 in addition to the components for interrupting the BMS signal to enable use with an electronic boiler.

As shown in Figure 2, the effect of extending the cooling period is to lower the temperature at the end of the cooling cycle.

Figure 7A shows typical values. The boiler thermostat temperature settings (before the settings are changed after the calibration) are at 72 degrees (lower) and 80 degrees (higher). The burn cycle last 5.5 minutes in this example, and the normal cooling cycle lasts 10 minutes.

A set of extended temperature thresholds are provided, such as 2, 4 and 6 degrees below the minimum temperature. Figure 7A shows the system set to the first extended threshold of 70 degrees, As shown, this results in an extended cooling period by an additional 5 minutes. The efficiency cycle carried out by the system of the invention is based on temperature detection rather than time monitoring as in the known approaches.

The minimum temperature is reduced by the fixed amount (such as 2 degrees below the starting point). Only when this reduced temperature is detected is the signal provided to fire the boiler, again by allowing the BMS enable command to be activated.

To determine if this level of extension of the cooling period is possible, the temperature is monitored over time. For example, the temperature is monitored periodically, for example every 4 seconds.

A fixed time period beyond the normal cooling time (i.e. τ1 to τ2; 10 minutes in this example) is allowed. The normal cooling time τ1 to τ2 is measured in the calibration phase.

If the temperature is maintained above this lower threshold for all of the additional time period, and for a set number of burn cycles (such as 5), this indicates that the temperature can be reduced further because the demand from the building is not large enough to need more rapid burn cycles.

For example, if cooling for a period of a set amount longer than the normal cooling time can be allowed without the lower temperature being reached, the cooling period can be extended further by lowering the temperature threshold by a further 2 degrees. This set amount may be 15% but it may be higher, for example 25% or 50%. It may for example lie in the range 10% to 60%. A longer cooling period may for example be associated with the lower temperature thresholds than for the higher temperature thresholds.

The firing time to raise the water to the upper temperature switching point will increase as a result, but this increase in firing time is relatively short compared to the increase in time of the cooling period, so that overall efficiency gains are obtained.

There is a fixed set of temperature adjustments, for example 2, 4 and 6 degrees below the lower temperature threshold. These have associated cooling period extensions at which the temperature is analysed to determine if the threshold needs to be changed. By way of example, the 2, 4 and 6 degree thresholds can be associated with 20%, 30% and 50% cooling period extensions.

The thresholds may be at 1 degree intervals instead of 2 degree intervals. Furthermore, there may be many more intervals, with the lowest temperature corresponding to a minimum temperature setting of the system which may be selected based on a minimum desired hot water temperature.

The system thus dynamically sets the temperature difference based on the temperature measurements at the relevant timing points.

As a building heats up, the boiler cooling period extends as it takes longer for the heat within the building to decay, and the switching to a lower temperature threshold is based on detection of this longer cooling period. The system continues extending the cooling period until the preset limits are reached, for example the lowest temperature setting. However, the control of the system is based on the temperature levels rather than based on fixing time periods, which gives stability and ensures that temperatures cannot drop below required levels, for example a minimum stored hot water temperature.

The use of three settings is of course just an example. There may be more settings, and they may differ by 1 degree instead of 2 degrees. Similarly, the associated extended cooling periods can be different. They may also be settable to different values. Figure 7B shows three fixed temperature thresholds of 70, 68 and 66 degrees (i.e. 2, 4 and 6 degrees below the lower threshold of 72 degrees). It shows how the first setting of 70 degrees provides a minimum extended cooling period, the second setting of 68 degrees provides a middle extended cooling period, and the third setting of 66 degrees provides a maximum extended cooling period.

If there is a decrease in demand on the boiler, cooling will be more gradual, so the lower temperature threshold will not be reached at the end of the extended time period (the additional 20%, then 30% then 50% in the example above). This signifies that the temperature is not dropping rapidly, so efficiency gains can be made by moving to a more extended cooling period. The temperature reached at the new extended time period is then monitored.

If there is an increase in demand on the boiler, cooling will be more rapid. A shorter extension period is then desired to make the boiler run more efficiently and to provide the required heat to the building sufficiently. If the lower threshold setting is too low, the building may cool too rapidly between firing cycles to meet the desired comfort levels, so the cooling period needs to be shortened.

Thus, if the lower temperature threshold is already reached at the time point being monitored, then the lower temperature threshold needs to be increased to a higher level, to reduce the extended cooling period.

The control is thus based on temperature detection, instead of setting time periods. The lower temperature threshold varies between the set of possible values dynamically based on the temperature reached at a given time after the cooling cycle begins. This is representative of the load and therefore is representative of whether extended cooling cycles are appropriate.

In this way, the system dynamically cycles between the different lower temperature thresholds based on the properties of the building, which influence the cooling cycle time.

Figure 8A shows how the cooling curve varies in dependence on the building load, and shows the different thresholds. Figure 8B shows a first cycle at the boiler thermostat setting of 72 degrees. This can be the last cycle of the calibration period. The burn cycle and cooling cycle times are measured, for example 3 minutes and 7 minutes. The 22 degree temperature line is the target room temperature.

The second cycle is for a first reduced lower setting of 70 degrees. The burn cycle has extended to 3.5m, and the cooling period has extended to 10m. If the time setting at which the assessment is made is for example at a threshold of 15% (7m +15% = 8.05m), a further reduction in the lower temperature threshold is possible, because the lower temperature has not been reached. The new temperature threshold is set and a new timing point for controlling the decision making for changing that temperature threshold.

The operation of the system thus comprises two main steps:

1 Start up and calibration procedure

The system measures the outgoing water temperature and registers the maximum and minimum temperature. This is carried out during normal boiler running. This provides a calibration of the temperature sensor of the system to the normal boiler operation.

The system also measures the durations of the firing and cooling cycles (i.e. time 0 to τ1 and τ1 to τ2).

In the first possible implemation, the boiler thermostat settings are raised by a fixed amount, such as 1 , 2 or 3 degrees. The maximum and minimum temperature points are then implemented by the system, with values that correspond to the previously set internal boiler values. In this way, the system of the invention controls the boiler based on the desired boiler settings, as previously set, whereas the internal boiler thermostat is effectively rendered out of circuit.

The amount by which the boiler thermostat settings are raised will depend on the accuracy of the electronic circuit to monitor the various temperatures.

The system is then for controlling the boiler based on the monitored temperature and the maximum and minimum set points. In the second possible implementation, there is no need to change the boiler thermostat settings.

2. During running:

The system overrides and controls the boiler using its own maximum and minimum set points as described above.

The calibration approach described above for the first implementation requires the boiler settings to be altered, so that the system can provide control at the temperatures set on the boiler thermostat.

The alternative second implementation is for the system to provide upper and lower temperatures which are below the boiler settings, for example 0.2, 0.5, 1 , 2 or 3 degrees below. The measured burn time and cool time will be almost identical because the temperature difference remains the same, particularly when a small temperature difference is used. This enables automatic calibration without needing the boiler settings to be altered as in the approach explained above. This provides a preferred approach. In this case, the system operates below the boiler set temperature settings, but this can just be 0.5 degrees degree below, or even less, for example down to 0.2 degress.

For example, if the upper thermostat setting is 80 degrees, then when the water reaches 79.5 degrees, the enable signal that told the boiler to fire is taken away from the boiler thermostat and is routed through the controller of the invention. This will cut the firing signal and cause the boiler to go into cooling. The cooling can then be extended to a lower temperature than the internal boiler setting, and once this lower temperature is reached, the enable signal can be returned to the control of the boiler.

The system can then also perform monitoring functions. In particular, it can detect any change in the boiler temperature settings and automatically adapt to them. It does this by performing a new calibration operation (as explained above) periodically. This can for example be every fixed number (e.g. 50) of burn/cool cycles. This calibration thus reveals any changed temperature settings on the boiler thermostat. However, it does not require any intervention to the boiler control circuitry or sensors.

In particular, this measuring cycle can be performed:

-when the system is powered up and switched on;

-when the system is switched on/off/on (so that a measuring cycle can be manually enforced);

-in response to a drop out of mains supply;

-periodically (such as every 50 Burn/Cool cycles), to detect an increase in boiler temperature setting. While the system is operational, it cannot detect any increase in the boiler temperature settings because the system is overriding any increased settings on the boiler. Thus, to detect increased temperature settings, a self-initiated measuring cycle (i.e. with the system function not operational) is performed followed by new maximum and minimum set points being defined, the fixed amount (such as 1 , 2 or 3 degrees) below the monitored temperature value.

The system can, however, detect a decrease in the boiler temperature settings while it is active, i.e. without needing a calibration operation. When the maximum temperature is not achieved this is indicative of a decrease in the boiler temperature setting. In response to detecting a drop in the boiler's temperature settings, the system will then perform a new calibration measuring cycle and set the required new maximum and minimum set points the fixed amount below monitored temperatures to be in control of the boiler.

The examples above are all based on modifying existing installations to provide improved performance. However, the underlying concepts can be applied to a new system designed from scratch.

The system preferably operates so that at no time is the water temperature from the boiler allowed to drop below a set level, such as 60 degrees (or a set temperature somewhere in the range 60 to 70 degrees). The maximum flow temperature which was set before implementing the system is also not increased. The invention is typically of interest for 50kW to 800kW boilers. Various modifications will be apparent to those skilled in the art.