Gas water heater thermocouple replacement guide. Learn how to test, identify problems and troubleshoot thermocouple on American, State, GE, Kenmore, Rheem, AO Smith, Bradford White and other brands.
The gas water heater thermocouple is the safety element that is designed to "inform" gas control valve is the pilot flame ON or OFF and open or close the gas to the main burner.
The thermocouple is a part of the pilot assembly where one end is always in contact with the pilot flame while the other side is connected to the gas control valve. The element is made of the copper tube and is very flexible and fragile.
Once you manually lit the pilot light, usually by the piezo igniter, it remains ON either water is heated or not. If the water temperature inside the heater’s tank drops below the set point, the thermostat activates and gas flows to the main burner. The pilot flame will then ignite the gas. When the water inside the tank reaches the temperature set on the thermostat, the thermostat interrupts the gas flow to the main burner.
The gas water heater thermocouple consists of two different metals, joined together, so when heated by the pilot flame a small electric current generates. The electric current, then, powers the electromagnet inside the gas valve and keeps it open.
If for any reason the pilot flame is gone, the thermocouple cools down, interrupting the electric current so the electromagnet closes the gas valve and shuts down the water heater. Sometimes it takes over a minute or two for thermocouple to cool down and close the valve.
During the initial start-up, piezo button will light the pilot, but has to be depressed for some time, as the thermocouple needs to get hot and produce the electricity.
If the pilot light won't stay lit, test the gas water heater thermocouple by keeping the pilot button depressed. Measure the current by using the multimeter device, set on millivolts. One probe of the meter should be connected to the copper sheath of the thermocouple and the other to the gas valve. If the reading shows 10 milivolts (White-Rodgers valve), 13 millivolts (Robertshaw control valve), or higher the thermocouple is good. Replace the element if the reading is below this value.