If your water heater has stopped heating, a tripped thermal switch may be to blame. In water heaters and many other types of home appliances, thermal switches disrupt power to the appliance's heating mechanisms when the appliance starts to overheat. Most thermal switches are triggered when the temperature of the water in the tank rises above 76.7 degrees Celsius (170 degrees Fahrenheit). While resetting the thermal switch on your water heater will allow it to operate again, the thermal switch may continue to trip if the underlying problem is not solved.
Look for a rectangular control circuit panel on your water heater. Depending on which brand and model of water heater you own, the control circuit panel may be located on the back or side of the appliance.
Locate your water heater's thermal reset switch or button. The thermal reset is usually a red or white switch or button at the centre of the control circuit panel.
Reset the thermal switch or button on your water heater. If your water heater has a thermal reset switch, flip it. If your water heater has a thermal reset button, press and hold it for up to 4 seconds to reset your appliance.
Resettable water heater switches like the kind discussed in this article are not to be confused with the single-use high-temperature limit switches, sometimes known as energy cut-off switches, found in some gas water heater models. While both types of switches are important safety devices, water heaters with high-temperature limit switches do not have thermal reset switches or buttons on their control circuit panels, so the thermal switch must be professionally replaced.
Do not attempt to reset the thermal switch or button in a gas water heater in which flammable vapours have ignited. If the thermal switch in your water heater was tripped, cutting off the supply of gas to your water heater, return the appliance to its manufacturer for repair or replacement.