Heater having over temperature control

A water heater having a snap disc temperature sensitive shut off device, said heater comprising:

• a body having walls defining a volume for holding water to be heated;
• an electric heating element thermally coupled to the body for heating water within the body;
• a temperature sensitive switch for sensing temperature of the water and shutting off electrical power to the electric heater when the sensed temperature of the water exceeds a predetermined maximum temperature limit, wherein the temperature sensitive switch is connected in series with the heating element;
• and
• a controller for monitoring a voltage potential applied to the temperature sensitive switch, said controller determining whether a failure has occurred in the heater as a function of the monitored voltage potential.

A detection circuit for detecting the state of a temperature sensitive switch for use in a heater, said detection circuit comprising:

• a first impedance line coupled to an input of the temperature sensitive switch;
• a second impedance line coupled to the input of the temperature sensitive switch;
• and
• a controller coupled to the first and second impedance lines, said controller applying a first signal to the first impedance line and monitoring a second signal at the second impedance line, wherein the controller determines if the temperature sensitive switch is open as a function of the second signal.

A method for determining the state of a temperature sensitive switch for use in a heater, said method comprising the steps of:

• applying a first signal to a first impedance line coupled to an input of a temperature sensitive switch;
• sensing a second signal on a second impedance line coupled to the input of the temperature sensitive switch;
• and
• determining whether the temperature sensitive switch is open as a function of the second signal.