How to Troubleshoot a Thermocouple

Gas water heaters are fitted with a single thermocouple located within the bottom of the tank. The thermocouple operates as a safety device by automatically turning off the supply of gas if the pilot light extinguishes. When a thermocouple is defective, it stops the flow of gas, and the pilot light will not stay lit. Determining whether a thermocouple is defective generally takes only a couple of minutes.

Take a defective thermocouple with you to the hardware store to ensure that you get the correct replacement.
  1. Follow the metal tubes from the bottom of the control box to where the tubes enter the tank. The metal panel on the side of the tank that the tubes pass through is the outer access panel. Pull the outer access panel off of the tank to reveal a second access panel.

  2. Lift the second access panel away from the tank to reveal the pilot light and the tip of the thermocouple.

  3. Shine a flashlight on the tip of the thermocouple inside the tank. The tip of the thermocouple must be positioned directly in front of the pilot flame. Bend the thermocouple's clip to reposition the tip of the thermocouple if necessary.

  4. Light the pilot light by following the instruction sticker affixed to the side of the tank.

  5. Observe the pilot flame to determine whether it extinguishes. If the flame does extinguish, a new thermocouple is necessary.