A heater thermostat tells the heater when to turn on and raise the temperature of the water inside or the air that circulates. A water heater thermostat works with a bi-metal disk that moves when it hits a certain temperature, activating or deactivating the circuit to the heating element
When purchasing a replacement heater thermostat for the water boiler, it is important to know the number of elements the heater is equipped with as well as the unit's voltage. The label on the water heater indicates the voltage, although it is printed on the heating element as well. For water heaters that feature two thermostats, if one breaks, it is wise to replace the other one at the same time.