USA Expert Plumbing

How to replace a water heater thermocouple

By USA Expert Plumbing Editorial Team. Updated . 2 min read.

Short answer

To replace a thermocouple on a standing-pilot gas water heater, turn the gas control to OFF and close the gas supply, let the burner cool, remove the burner assembly or access cover, swap the thermocouple for one of the right length, reassemble, relight the pilot and check for leaks. Heaters with sealed combustion chambers may need a manufacturer kit.

In this guide
  1. Before you start
  2. Step by step
  3. If the pilot still goes out
  4. Sealed combustion chambers

A worn thermocouple is the most common reason a gas water heater pilot will not stay lit. On many older, simple heaters, replacing it is a manageable job. On newer sealed designs it is harder, and a pro may be the better call.

If you smell gas, do not touch switches or light anything. Leave the house and call your gas utility from outside.

Before you start

  • Confirm the heater uses a thermocouple, not a thermopile and electronic control with a status light.
  • Get the manufacturer's replacement part or a universal thermocouple of the correct length.
  • Tools: an adjustable or open-end wrench, a flashlight, and the heater's manual.

Step by step

  1. Turn the gas control knob to OFF and close the gas shutoff valve to the heater. Wait for the burner area to cool.
  2. Remove the outer and inner access covers.
  3. Disconnect the thermocouple, pilot tube and burner supply from the gas control.
  4. Slide out the burner assembly carefully, or remove the thermocouple bracket if it is reachable.
  5. Unclip the old thermocouple from the pilot bracket and install the new one in the same position, with its tip in the pilot flame path.
  6. Reinstall the burner assembly and reconnect the fittings. Tighten the thermocouple nut snugly; overtightening can damage it.
  7. Open the gas supply and relight the pilot following the label. Hold the pilot button as long as the instructions say.
  8. Check the fittings you touched for leaks with soapy water; bubbles mean a leak.
  9. Replace the covers, including any inner door gasket, and set the temperature.

If the pilot still goes out

The thermocouple may not have been the problem. A dirty pilot, a weak flame, drafts, a clogged combustion air intake or a failing gas control can all put the pilot out. See our water heater thermocouple replacement cost guide for what a pro charges.

Sealed combustion chambers

Most gas water heaters built for flammable vapor protection have a sealed burner compartment. The burner, pilot and thermocouple may come out as one assembly, and the inner door gasket must be replaced if it is damaged. Some manufacturers sell the pilot and thermocouple only as a kit. Follow the manufacturer's instructions exactly, and if the door seal cannot be restored, call a technician.

Common questions

How long does it take to replace a thermocouple?

For an experienced homeowner, often about an hour. Sealed combustion chambers take longer.

Are thermocouples universal?

Many are, but length and fitting matter. The manufacturer's part is the safest choice.

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