Gas Water Heater
Thermocouple Replacement

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.

Content

What is a thermocouple

Every gas water heater that is using pilot light has the burner assembly consisted of the following elements:

  • Main burner orifice
  • Gas supply tube for the main burner
  • Pilot burner
  • Pilot burner orifice
  • Pilot burner gas supply tube
  • Thermocouple

gas water heater thermocoupleThe 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.

How the thermocouple works

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.


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Thermocouple problems

  • Pilot light does not stay lit when the ignition button is released. The possible problem is that you might have a faulty or loose thermocouple or connection. Defective element cannot be repaired so the replacement is the only option. These elements are not expensive. If the screw nut was loose tighten it.
  • If you experience pilot outage, thermocouple might not be in contact with the pilot light. Position it properly and according to the manufacturer specs, so it is fully immersed inside the pilot flame.

How to test a thermocouple

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.

How to replace a gas water heater thermocouple

  • Turn OFF the gas supply to the water heater and on the gas control valve.
  • The thermocouple has two ends. Disconnect one end from the gas control valve and the other end from the pilot bracket (you can use pliers). Be careful not to damage the copper tube... it is very fragile.
  • Install a new element into the pilot bracket, and make sure to be fully engaged. Connect the other side of the element to the control valve - finger tight and 1/4 turn.
  • To resume the operation follow the lighting instructions found on the label.

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