Water heater and control

• US 6,955,301 B2
• Filed: 03/05/2003
• Issued: 10/18/2005
• Est. Priority Date: 03/05/2003
• Status: Expired due to Term

• Current Assignee: Ademco Inc. (Resideo Technologies, Inc.)
• Original Assignee: Honeywell International Inc.
• Inventors: Chian, Brent, Munsterhuis, Sybrandus B. V.
• Primary Examiner(s): Tanner, Harry B.
• Application Number:
  US10/382,056
• Publication Number:
  US 20040173600A1
• Time in Patent Office: 958 Days
• Field of Search: 236/20.R, 236/78.B, 219/510, 219/494, 122/14.22
• US Class Current: 236/20.00R
• CPC Class Codes: F24H 1/205 with furnace tubes
• CPC Class Codes: F24H 15/128 Preventing overheating
• CPC Class Codes: F24H 15/156 Reducing the quantity of energy consumed; Increasing efficiency
• CPC Class Codes: F24H 15/174 Supplying heated water with desired temperature or desired range of temperature
• CPC Class Codes: F24H 15/225 at different heights of the tank
• CPC Class Codes: F24H 15/281 Input from user
• CPC Class Codes: F24H 15/31 of valves having only one inlet port and one outlet port, e.g. flow rate regulating valves
• CPC Class Codes: F24H 15/414 using electronic processing, e.g. computer-based
• CPC Class Codes: F24H 9/2035 using fluid fuel

Abstract

An improved heater and method of controlling the same is provided. The water heater has the combination of a tank for holding water, a heater for heating the water, a controller having logic to regulate the heater, and first and second sensors. Each of the sensors detects the water temperature at different areas within the water heater. The sensors also provide the controller with signals corresponding to the detected water temperature. In response to these signals, the controller regulates the heater when at least one of the signals of the first and second sensors satisfies at least one predetermined state condition.

Claims

1. A water heater comprising in combination:

a tank for holding water having at least one water temperature, wherein the tank has a top and a bottom separated by a vertical distance when the water heater is in a normal vertical operational position;

a heater for heating the water, wherein the heater has hither and lower outputs;

first and second sensors, wherein the first and second sensors are vertically displaced an the tank when the water heater is in a normal operational position, and wherein the first sensor is located closer to the top of the tank than the second sensor, and

a controller having logic to regulate the heater,

(a) wherein the first sensor is operable to detect a first water temperature that is less than a maximum-temperature threshold and responsively provide a non-maximum-temperature signal, wherein the second sensor is operable to detect a second water temperature that is less than a first-setpoint-temperature threshold and responsively provide a first-setpoint-temperature signal, and wherein after determining that the non-maximum-temperature and first-setpoint-temperature signals satisfy respective non-maximum-temperature and first-setpoint-temperature state conditions, the logic regulates the heater to drive the heater to the higher output;

(b) wherein the first sensor is operable to detect a water temperature that is greater than a maximum-temperature threshold and responsively provide a maximum-temperature signal, wherein the second sensor is operable to detect a third water temperature and responsively provides a third temperature signal, and wherein after determining that the maximum-temperature and third-temperature signals satisfy respective maximum-temperature and third-temperature state conditions, the logic regulates the heater to drive the heater to the lower output;

(c) wherein the first sensor is operable to detect a fourth water temperature and responsively provide a fourth-temperature signal, wherein the second sensor is operable to detect a water temperature that is greater than a second-setpoint-temperature threshold and responsively provide a cut-off signal, and wherein after determining that the fourth-temperature and cut-off signals satisfy respective fourth-temperature and second-setpoint-temperature state conditions, the logic regulates the heater to drive the heater to the lower output;

(d) wherein the first sensor is operable to detect a water temperature that is less than a maximum-temperature threshold and responsively provide a non-maximum-temperature signal, wherein the second sensor is operable to detect a water temperature that is less than a second-setpoint-temperature threshold and responsively provide a non-cut-off signal, and wherein after determining that the non-maximum-temperature and non-cut-off signals satisfy respective non-maximum-temperature and non-cut-off state conditions, the logic, if already regulating the heater to drive the heater to the higher output, continues to regulate the heater to drive to the heater to the higher output; and

(e) wherein the first sensor is operable to detect a water temperature that is less than a maximum-temperature threshold and responsively provide a non-maximum-temperature signal, wherein the second sensor is operable to detect a water temperature that is less than a second-setpoint-temperature threshold and responsively provide a non-cut-oft signal, and wherein after determining that the non-maximum-temperature and non-cut-off signals satisfy respective non-maximum-temperature and non-cut-off state conditions, the logic, if already regulating the heater to drive the heater to the lower output, continues to regulate the heater to drive the heater to the lower output.

2. The water heater of claim 1, wherein the controller has additional logic to receive the at least one signal of the first and second sensors.

3. A water heater comprising in combination:

a tank for holding water having at least one water temperature, wherein the tank has a top and a bottom separated by a vertical distance when the water heater is in a normal vertical operational position;

a heater for heating the water, wherein the heater has higher and lower outputs;

first and second sensors, wherein the first and second sensors are vertically displaced on the tank when the water heater is in a normal operational position, wherein the first sensor is located closer to the top of the tank than the second sensor, wherein the first sensor is operable to detect a first water temperature that is less than a maximum-temperature threshold and responsively provide a non-maximum-temperature signal, and wherein the second sensor is operable to detect a second water temperature that is less than a first-setpoint-temperature threshold and responsively provide a first-setpoint-temperature signal; and

a controller having logic to regulate the heater, wherein after determining that the non-maximum-temperature and first-setpoint-temperature signals satisfy respective non-maximum-temperature and first-setpoint-temperature state conditions, the logic regulates the heater to drive the heater to the higher output.

4. The water heater of claim 3, wherein the higher output is an on state.

5. A water heater comprising in combination:

a tank for holding water having at least one water temperature, wherein the tank has a top and a bottom separated by a vertical distance when the water heater is in a normal vertical operational position;

a heater for heating the water, wherein the heater has higher and lower outputs;

first and second sensors, wherein the first and second sensors are vertically displaced on the tank when the water heater is in a normal operational position, wherein the first sensor is located closer to the top of the tank than the second sensor, wherein the second sensor is operable to detect a water temperature and responsively provides a second temperature signal, and wherein the first sensor is operable to detect a water temperature that is greater than a maximum-temperature threshold and responsively provides a maximum-temperature signal; and

a controller having logic to regulate the heater, wherein after determining that the maximum-temperature and second-temperature signals satisfy respective maximum-temperature-threshold and second temperature state conditions, the logic regulates the heater to drive the heater to the lower output.

6. The water heater of claim 5, wherein the lower output is an off state.

7. A water heater comprising in combination:

a tank for holding water having at least one water temperature, wherein the tank has a top and a bottom separated by a vertical distance when the water heater is in a normal vertical operational position;

a heater for heating the water, wherein the heater has higher and lower outputs;

first and second sensors, wherein the first and second sensors are vertically displaced on the tank when the water heater is in a normal operational position, wherein the first sensor is located closer to the top of the tank than the second sensor, wherein the first sensor is operable to detect a first water temperature and responsively provide a first temperature signal, and wherein the second sensor is operable to detect a water temperature that is greater than a second-setpoint-temperature threshold and responsively provide a cut-off signal; and

a controller having logic to regulate the heater, wherein after determining that the first temperature and cut-off signals satisfy respective first-temperature and second-setpoint-temperature state conditions, the logic regulates the heater so as to drive heater to the lower output.

8. The water heater of claim 7, wherein the lower output is an off state.

9. A water heater comprising in combination:

a tank for holding water having at least one water temperature, wherein the tank has a top and a bottom separated by a vertical distance when the water heater is in a normal vertical operational position;

a heater for heating the water, wherein the heater has higher and lower outputs;

first and second sensors, wherein the first and second sensors are vertically displaced on the tank when the water heater is in a normal operational position, wherein the first sensor is located closer to the top of the tank than the second sensor, wherein the first sensor is operable to detect-temperature threshold and responsively provide a non-maximum-temperature signal, wherein the second sensor is operable to detect a second water temperature that is less than a setpoint-temperature threshold and responsively provide a non-cut-off signal; and

a controller having logic to regulate the heater, wherein after determining that the non-maximum-temperature and non-cut-off signals satisfy respective non-maximum-temperature and non-cut-off state conditions, the logic, if already regulating the heater to drive the heater to the higher output, continues to regulate the heater to drive the heater to the higher output.

10. The water heater of claim 9, wherein the higher output is an on state.

11. A water heater comprising in combination:

a tank for holding water having at least one water temperature, wherein the tank has a top and a bottom separated by a vertical distance when the water heater is in a normal vertical operational position;

a heater for heating the water, wherein the heater has higher and lower outputs;

first and second sensors, wherein the first and second sensors are vertically displaced on the tank when the water heater is in a normal operational position, wherein the first sensor is located closer to the top of the tank than the second sensor, wherein the first sensor is operable to detect a first water temperature that is less than a maximum-temperature threshold and responsively provide a non-maximum-temperature signal, wherein the second sensor is operable to detect a second water temperature that is less than a second-setpoint-temperature threshold and responsively provide a non-cut-off signal; and

a controller having logic to regulate the heater, wherein after determining that the non-maximum-temperature and non-cut-off signals satisfy respective non-maximum-temperature and non-cut-off state conditions, the logic, if already regulating the heater to drive the heater to the lower output, continues to regulate the heater to drive the heater to the lower output.

12. The water heater of claim 11, wherein the lower output is an off state.

13. The water heater of claim 12, wherein the controller detects an average rate of cooling of at least one of the first and second water temperatures that is faster than a cooling rate threshold and responsively drives the heater to the higher output.

14. The water heater of claim 13, wherein the higher output is an on state.

15. The water heater of claim 12, wherein

upon detecting a water temperature that is less than a maximum-temperature threshold, the first sensor provides a non-maximum-temperature signal, upon detecting a water temperature that is less than the second-setpoint-temperature threshold, the second sensor provides a non-cut-off signal, and upon the controller detecting a rate of cooling of a water temperature that is faster than a cooling rate threshold, the controller provides a cooling rate signal, which in combination with the non-maximum-temperature and non-cut-off signals causes the controller to drive the heater at the higher output if already regulating the heater to drive the heater to the lower output.

16. The water heater of claim 15, wherein the lower output is an off state and the higher output is an on state.

31. The water heater of claim 12, wherein the controller has a fail-safe output for inhibiting operation of the water heater, and further comprising a third sensor wherein the third sensor is vertically displaced on the tank when the water heater is in a normal operational position, wherein the third sensor is located above the first sensor, wherein the first sensor is operable to detect a water temperature that is greater than an overheat-temperature-threshold and responsively an overheat-temperature signal, and wherein responsive to the overheat-temperature signal, the logic inhibits the operation of the water heater.

17. A water heater comprising in combination:

a tank for holding water having at least one water temperature, wherein the tank has a top and a bottom separated by a vertical distance when the water heater is in a normal vertical operational position;

a heater for heating the water, wherein the heater has higher and lower outputs;

first and second sensors, wherein the first and second sensors are vertically displaced on the tank when the water heater is in a normal operational position, wherein the first sensor is located closer to the top of the tank than the second sensor, wherein the first sensor is operable to detect a water temperature that is within an ON-zone and responsively provide a first-on-state signal, and wherein the second sensor is operable to detect a water temperature that is within the ON-zone and responsively provide a second-on-state signal; and

a controller having logic to regulate the heater, wherein after determining that the first-on-state and second-on-state signals satisfy respective first-on-state and second-on-state conditions, the logic regulates the heater to drive the heater to the higher output.

18. A water heater comprising in combination;

a tank for holding water having at least one water temperature, wherein the tank has a top and a bottom separated by a vertical distance when the water heater is in a normal vertical operational position;

a heater for heating the water, wherein the heater has higher and lower outputs;

first and second sensors, wherein the first and second sensors are vertically displaced on the tank when the water heater is in a normal operational position, wherein the first sensor is located closer to the top of the tank than the second sensor, wherein the first sensor is operable to detect a water temperature that is within an OFF zone and responsively provides an off-state signal; and

a controller having logic to regulate the heater, wherein after determining that the oft-state signal satisfies an off-state condition, the logic regulates the heater to drive the heater to the lower output.

19. A water heater comprising in combination:

a tank for holding water having at least one water temperature, wherein the tank has a top and a bottom separated by a vertical distance when the water heater is in a normal vertical operational position;

a heater for heating the water, wherein the heater has higher and lower outputs;

first and second sensors, wherein the first and second sensors are vertically displaced on the tank when the water heater is in a normal operational position, wherein the first sensor is located closer to the top of the tank than the second sensor, wherein the second sensor is operable to detect a water temperature that is within an OFF zone and responsively provides a off-state signal; and

a controller having logic to regulate the heater, wherein after determining that the off-state signal satisfies an off-state condition, the logic regulates the heater to drive the heater to the lower output.

20. A water heater comprising in combination:

a tank for holding water having at least one water temperature, wherein the tank has a top and a bottom separated by a vertical distance when the water heater is in a normal vertical operational position;

a heater for heating the water, wherein the heater has higher and lower outputs;

first and second sensors, wherein the first and second sensors are vertically displaced on the tank when the water heater is in a normal operational position, wherein the first sensor is located closer to the top of the tank than the second sensor, wherein the first sensor is operable to detect a first water temperature that is within an OFF zone and responsively provides a first-off-state signal, and wherein the second sensor is operable to detect a second water temperature that is within the OFF zone and responsively provide a second-off-state signal; and

a controller having logic to regulate the heater, wherein after determining that the first-off-state and second-off-state signals satisfy respective first-off-state and second-off-state conditions, the logic regulates the heater to drive the heater to the lower output.

21. The water heater of claim 20, wherein the OFF zone includes a step boundary to control an average of the first and second water temperatures at approximately a setpoint temperature while ensuring that water drawn from the tank is at or above the setpoint temperature after completion of a heating cycle.

22. The water heater of claim 21 wherein the first and second sensors detect water temperatures that are greater than the step boundary and responsively provide first and second off-state signals, and responsive to the first and second off-state signals, the controller drives the heater to the lower output.

23. The water heater of claim 20, wherein

the OFF zone includes a boundary that provides a constant average temperature threshold to control an average of the first and second water temperatures at a predetermined amount below a setpoint temperature while ensuring that water drawn from the tank is at or above the setpoint temperature after completion of a heating cycle;

the first and second sensors detect water temperatures that are greater than the boundary and responsively provide first and second off-state signals, and

responsive to the first and second off-state signals, the logic regulates the heater to drive the heater to the lower output.

24. A water heater comprising in combination:

a tank for holding water having at least one water temperature, wherein the tank has a top and a bottom separated by a vertical distance when the water heater is in a normal vertical operational position;

a heater for heating the water, wherein the heater has higher and lower outputs;

first and second sensors, wherein the first and second sensors are vertically displaced on the tank when the water heater is in a normal operational position, wherein the first sensor is located closer to the top of the tank than the second sensor, wherein the first sensor is operable to detect a first water temperature that is within a COOLING-RATE DEPENDENT-ON zone and responsively provide a first-dependent-state signal, and wherein the second sensor is operable to detect a second water temperature that is within the COOLING-RATE DEPENDENT-ON zone and responsively provide a second-dependent-state signal, and

a controller having logic to regulate the heater, wherein after determining that the first-dependent-state and second-dependent-state signals satisfy respective first-off-state and second-off-state conditions, the logic, if already regulating the heater to drive the heater to the higher output, continues to regulate the heater to drive the heater to the higher output.

25. A water heater comprising in combination:

a tank for holding water having at least one water temperature, wherein the tank has a top and a bottom separated by a vertical distance when the water heater is in a normal vertical operational position;

a heater for heating the water, wherein the heater has higher and lower outputs;

first and second sensors, wherein the first and second sensors are vertically displaced on the tank when the water heater is in a normal operational position, wherein the first sensor is located closer to the top of the tank than the second sensor, wherein the first sensor is operable to detect a first water temperature that is within a COOLING-RATE DEPENDENT-ON zone and responsively provide a first-dependent-state signal, and where the second sensor is operable to detect a second water temperature that is within the COOLING-RATE-DEPENDENT-ON zone and responsively provide a second-dependent-state signal, and

a controller having logic to regulate the heater, wherein after determining that the first-dependent-state and second-dependent-state signals satisfy respective the first-dependent-state and second-dependent-state conditions, the logic, if already regulating the heater so as to drive the heater to the lower output, continues to regulate the heater to drive the heater to the lower output.

26. The water heater of claim 25, wherein the controller detects an average rate of cooling of at least one of the first and second water temperatures that is faster than a cooling-rate threshold, and responsively drives the heater to the higher output.

27. The water heater of claim 25, wherein

the controller detects when the heater has not been driven to the higher output for a period exceeding a time threshold and responsively provides a time-dependent-on signal, and

responsive to the time-dependent-on signal, the controller maintains the heater at the lower output.

28. A water heater comprising in combination:

a tank for holding water having at least one water temperature, wherein the tank has a top and a bottom separated by a vertical distance when the water heater is in a normal vertical operational position;

a heater for heating the water, wherein the heater has higher and lower outputs;

first and second sensors, wherein the first and second sensors are vertically displaced on the tank when the water heater is in a normal operational position, wherein the first sensor is located closer to the top of the tank than the second sensor, wherein the first sensor is operable to detect a water temperature that is within a NO-CHANGE zone and responsively provide a first-maintain-status signal, and wherein the second sensor is operable to detect a water temperature that is within the NO-CHANGE zone and responsively provide a second-maintain-status signal, and

a controller having logic to regulate the heater, wherein after determining that the first-maintain-status and second-maintain-status signals satisfy respective the first-maintain-status and second-maintain-status conditions, the logic, if already regulating the heater to drive the heater to the higher output, continues to regulate the heater to drive the heater to the higher output.

29. A water heater comprising in combination:

a tank for holding water having at least one water temperature, wherein the tank has a top and a bottom separated by a vertical distance when the water heater is in a normal vertical operational position;

a heater for heating the water, wherein the heater has higher and lower outputs;

first and second sensors, wherein the first and second sensors are vertically displaced on the tank when the water heater is in a normal operational position, wherein the first sensor is located closer to the top of the tank than the second sensor, wherein the first sensor is operable to detect a first water temperature that is within a NO-CHANGE zone and responsively provide a first-maintain-status signal, and wherein the second sensor is operable to detect a first water temperature that is within the NO-CHANGE zone and responsively provide a second-maintain-status signal, and

a controller having logic to regulate the heater, wherein after determining that the first-maintain-status and second-maintain-status signals satisfy respective the first-maintain-status and second-maintain-status conditions, the logic, if already regulating the heater to drive the heater to the lower output, continues to regulate the heater to drive the heater to the lower output.

30. A water heater comprising in combination:

a tank for holding water having at least one water temperature, wherein the tank has a top and a bottom separated by a vertical distance when the water heater is in a normal vertical operational position;

a heater for heating the water, wherein the heater has higher and lower outputs;

first and second sensors, wherein the first and second sensors are vertically displaced on the tank when the water heater is in a normal operational position, wherein the first sensor is located closer to the top of the tank than the second sensor, wherein upon the first sensor detecting a water temperature that is within an ON zone, the first sensor provides a first-on-state signal, and upon the second sensor detecting a water temperature that is within the ON zone, the second sensor provides a second-on-state signal, which in combination with the first-on-state-condition signal causes the controller to drive the heater to the higher output,

upon the first sensor detecting a water temperature that is within an OFF zone, the first sensor provides a first-off-state signal to cause the controller to drive the heater to the lower output,

upon the second sensor detecting a water temperature that is within the OFF zone, the second sensor provides a second-off-state signal to cause the controller to drive the heater to the lower output,

upon the first sensor detecting a water temperature that is within a NO-CHANGE zone, the first sensor provides a first-maintain-status signal, and upon the second sensor detecting a water temperature that is within the NO-CHANGE zone, the second sensor provides a second-maintain-status signal, which in combination with the first-maintain-status signal causes the controller to (i) maintain the heater at the higher output when the controller is presently driving the heater to the higher output and (ii) to maintain the heater at the lower output when the controller is presently driving the heater to the lower output,

upon the first sensor detecting a water temperature that is within a COOLING-RATE DEPENDENT-ON zone, the first sensor provides a first-dependent-state signal, upon the second sensor detecting a water temperature that is within the COOLING-RATE DEPENDENT-ON zone, the second sensor provides a second-dependent-state signal, which in combination with the second-dependent-state signal causes the controller to drive the heater to the higher output when the controller is presently driving to the higher output,

upon detecting a first water temperature that is within a COOLING-RATE DEPENDENT-ON zone, the first sensor provides a third-dependent-state signal, upon detecting a second water temperature that is within the COOLING-RATE DEPENDENT-ON zone, the second sensor provides a fourth-dependent-state signal, and upon the controller detecting an average rate of cooling of at least one of the first and second water temperatures that is faster than a cooling-rate threshold, the controller providing a cooling-rate signal, which in combination with the third-dependent-state signal and the fourth-dependent-state signal causes the controller to drive the heater to the higher output.

32. A water heater comprising in combination:

a tank for holding water having at least one water temperature, wherein the tank has a top and a bottom separated by a vertical distance when the water heater is in a normal vertical operational position;

a heater for heating the water, wherein the heater has higher and lower outputs;

first and second sensors, wherein the first and second sensors are vertically displaced on the tank when the water heater is in a normal operational position, wherein the first sensor is located closer to the top of the tank than the second sensor, wherein the first sensor is operable to detect a first water temperature and responsively provide a first temperature signal, wherein the second sensor is operable to detect a water temperature that is greater than an overheat-temperature threshold and responsively provide an overheat-temperature signal; and

a controller having logic to regulate the heater and a fail-safe output for inhibiting operation of the water heater, wherein after determining that the overheat-temperature signal satisfies an overheat-temperature state condition, the logic inhibits the operation of the water heater.

33. A controller assembly for controlling a heater in a water heater, the water heater holding water having at least one water temperature and having a water exit and a water entrance, the controller assembly comprising in combination:

first and second sensors, wherein the first sensor is operable to close to the water exit a water temperature that is less than a maximum-temperature threshold and responsively provide a non-maximum-temperature signal, and wherein the second sensor is operable to detect close to the water entrance a water temperature that is less than a first-setpoint-temperature threshold and responsively provide a first-setpoint-temperature signal, and

a controller having logic to regulate the heater, wherein the heater has higher and lower outputs, wherein after determining that the non-maximum-temperature and first-setpoint-temperature signals satisfy the non-maximum-temperature and first-setpoint-temperature state conditions, the logic drives the heater to the higher output.

34. The controller assembly of claim 33, wherein,

the first sensor is operable to detect close to the water exit a water temperature that is greater than a maximum-temperature threshold and responsively provide a maximum-temperature signal, and

responsive to the maximum-temperature signal, the logic drives the heater to the lower output.

35. The controller assembly of claim 33, wherein,

the second sensor is operable to detect close to the water entrance a water temperature greater than a second-setpoint-temperature threshold and responsively provide a cut-off signal, and

responsive to the cut-off signal, the logic drives the heater to the lower output.

36. The controller assembly of claim 33, wherein,

the logic drives the heater to the higher output,

the first sensor is operable to detect close to the water exit a water temperature that is less than a maximum-temperature threshold and responsively provide a non-maximum-temperature signal,

the second sensor is operable to detect close to the water entrance a water temperature that is less than a second-setpoint temperature threshold and responsively provide a non-cut-off signal,

responsive to the non-maximum-temperature and non-cut-off signals, the logic maintains driving the heater to the higher output.

37. The controller assembly of claim 33, wherein,

the logic drives the heater to the lower output,

the first sensor is operable to detect detests close to the water entrance a first water temperature that is less than a maximum-temperature threshold and responsively provide a non-maximum-temperature signal,

the second sensor is operable to detect close to the water entrance a second water temperature that is less than a second-setpoint-temperature threshold and responsively provide a non-cut-off signal, and

responsive to the non-maximum-temperature and non-cut-off signals, the logic maintains driving the heater to the lower output.

38. The water heater of claim 37, wherein the logic detects an average rate of cooling of at least one of the first and second water temperatures that is faster than a cooling rate threshold and responsively drives the heater to the higher output.

39. A method for regulating a heater in a water heater, wherein the water heater has a water exit and a water entrance, and wherein the heater has lower and hither outputs, the method comprising in combination:

detecting close to the water exit a water temperature that is less than a maximum-temperature threshold and responsively providing a non-maximum-temperature signal,

detecting close to the water entrance a water temperature that is less than a first-setpoint-temperature threshold and responsively providing a first-setpoint-temperature signal, and

determining whether the non-maximum-temperature and first-setpoint-temperature signals satisfy respective non-maximum-temperature and first-setpoint-temperature state conditions; and

regulating the heater to drive the heater to the higher output in response to the non-maximum-temperature and first-setpoint-temperature signals satisfying respective non-maximum-temperature and first-setpoint-temperature state conditions.

40. A method for regulating a heater in a water heater, wherein the water heater has a water exit and a water entrance, and wherein the heater has lower and higher outputs, the method comprising in combination:

detecting close to the water entrance a first water temperature and responsively providing a first-temperature signal;

detecting close to the water exit a water temperature that is greater than a maximum-temperature threshold and responsively providing a maximum-temperature signal; and

determining whether the maximum-temperature signal satisfies at least one maximum-temperature state condition; and

regulating the heater to drive the heater to the lower output in response to the maximum-temperature signal satisfying at least one maximum-temperature state condition.

41. A method for regulating a heater in a water heater, wherein the water heater has a water exit and a water entrance, and wherein the heater has lower and higher outputs, the method comprising in combination:

detecting close to the water exit a first water temperature and responsively providing a first water temperature signal;

detecting close to the water entrance a water temperature greater than a second-setpoint-temperature threshold and responsively providing a cut-off signal; and

determining whether the cut-off signal satisfies a cut-off state condition; and

regulating the heater to drive the heater to the lower output in response to the cut-off signal satisfying the cut-off state condition.

42. A method for regulating a heater in a water heater, wherein the water heater has a water exit and a water entrance, and wherein the heater has lower and higher outputs, the method comprising in combination:

detecting close to the water exit a water temperature that is less than a maximum-temperature threshold and responsively providing a non-maximum-temperature signal,

detecting close to the water entrance a water temperature that is less than a second-setpoint-temperature threshold and responsively providing a non-cut-off signal,

determining whether the non-maximum-temperature and non-cut-off signals satisfy respective non-maximum-temperature and non-cut-off state conditions; and

responsive to determining whether the non-maximum-temperature-state and non-cut-off signals satisfy respective non-maximum-temperature and non-cut-off state conditions, continuing to regulate the heater to drive the heater at the lower output when the heater is being driven at a lower output.