How To Clean the Thermocouple on a Water Heater

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If the hot water temperature setting on your washing machine doesn’t seem to be working, you’ve been washing your dishes with lukewarm water, or you’ve been experiencing the dreaded cold shower, chances are your home’s water heater is malfunctioning. If you have a gas water heater, a dirty thermocouple could be to blame.

What is a thermocouple and why does my water heater need one?

Gas water heaters which use a pilot to light the burner will also have a thermocouple or thermopile to monitor the pilot (a thermopile is, essentially, multiple thermocouples connected in a series making the component more sensitive than a single thermocouple). If the pilot light goes out, the thermocouple acts as a safety device by preventing the gas valve from opening and potentially filling the area surrounding the water heater with natural gas. A faulty thermocouple, or one that is simply dirty, may consistently prevent the gas valve from opening or the pilot from staying lit. The end result is the burner assembly doesn’t produce a flame and the water in the tank is left unheated.

Be aware, if the pilot light goes out, you will need to relight it following the water heater manufacturer’s instructions. Newer model water heaters will have a pilot setting on the gas valve and a spark electrode to light the pilot. Older models will have the pilot setting, but you will need to manually relight the pilot with a long match or lighter.

Accessing the thermocouple

The thermocouple is usually mounted on the burner assembly located near the bottom of the water heater tank. The steps required to access the thermocouple will vary depending on the water heater model, but here are some general guidelines you can follow:

  • Before you begin, be sure to unplug the water heater’s power cord and shut off the gas supply.
  • If necessary, unthread any mounting screws and remove the burner access cover.
  • Next, unthread the nuts or screws securing the burner plate itself.
  • Unthread the nut to detach the burner supply tube from the gas or control valve. Be aware, you may need to detach a pilot supply tube as well.
  • Disconnect any wires from the valve and unthread the nut to release the thermocouple if required by your model.
  • If applicable, detach the vapor sensor from the tank base.
  • You can now pull the burner assembly away from the tank to access the thermocouple.

Cleaning the thermocouple

You can use Emery cloth sandpaper to gently clean any debris or build-up from the end of the thermocouple. If present, you should also clean off any corrosion where the power wire connects to the thermocouple terminal. Be aware, you may need to detach the thermocouple from the burner assembly to clean it thoroughly. Use a lint-free cloth to wipe the component clean of any remaining debris. Secure the thermocouple to the burner assembly if required.

  • Reseat the burner assembly in the tank, making sure to rest the burner tube in the bracket if applicable.
  • Thread and tighten the mounting nuts or screws to secure the burner plate to the tank.
  • Reattach the vapor sensor to the tank base if necessary.
  • Reconnect the wires to the gas valve and, if applicable, secure the thermocouple to the valve.
  • Reattach the burner supply tube to the valve, as well as the pilot supply tube if necessary.
  • Replace the burner access cover and secure as needed.
  • Turn the gas supply back on and plug the water heater power cord back in.
  • Relight the pilot and confirm the water heater is heating the water as expected.

Find the right water heater parts with Repair Clinic

If the water heater is still failing to heat the water, the thermocouple may be completely defective, the pilot itself could be restricted, the igniter could be faulty, the gas valve could be malfunctioning, or the pressure switch in the power vent blower housing may have failed. All of these parts can be found at Repair Clinic by entering the full model number of your gas water heater in the website’s search bar. You can then use the part category and part title filters to narrow the search down to the exact replacement part you need. Repair Clinic carries water heater parts for all the top brands like AO Smith, Bradford White, Lennox, and Honeywell, but you’ll want to make sure you’re purchasing the specific part that fits your particular water heater.

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