Water Heater Thermocouple Replacement (Why and How!)

If your gas water heater’s pilot light won’t stay lit, there’s a very good chance you need a water heater thermocouple replacement.

I’m going to tell you what a thermocouple is, what it does, the signs that it has gone bad, and how to replace it. Let’s get started.

What is a Water Heater Thermocouple?

A water heater thermocouple is a sensor that turns off the gas supply when the pilot light goes out. This operational and safety feature is also known as a flame or heat sensor and its function is to control the flow of gas into the burner.

How Do You Know if Your Water Heater Thermocouple is Bad?

A bad thermocouple is the most common reason for a water heater pilot light that won’t stay lit. And it’s not unusual for it to wear out.

Ironically, this happens sometimes due to the very nature of the device: the constant change in temperature results in a worn-out or “stressed” thermocouple. It can also malfunction when residue or soot buildup causes the flame to be blocked.

A bad thermocouple can result from the following:

• A bent thermocouple: If the flame isn’t slightly touching the thermocouple, it could be bent or misaligned. Simply bend it toward the pilot.
• A dirty thermocouple: As noted above, soot or other residue can prevent it from working. To solve this problem, remove the thermocouple and clean it off. Caution: Always turn off the gas valve before you remove a thermocouple.
• A broken thermocouple: This can result from wearing out. If electricity does not run through the thermocouple, it’s broken. To test this, use a multimeter. If the voltage is less than 20MV, it is damaged and needs to be replaced. Read below for instructions on how to do that.

Water Heater Thermocouple Replacement: Instructions

1. Disconnect the Old Thermocouple

• Turn the gas control knob to OFF and close the gas shutoff valve.
• With an open-end wrench, loosen the nut that secures the water heater thermocouple to the control unit, then unscrew it.
• Pull down on the copper lead to detach the end of the thermocouple from the control unit.
• There may be a second nut attaching the thermocouple tip to the pilot bracket; unscrew it and slide it back along the copper lead.
• Grip the base of the thermocouple and pull firmly, sliding it out of the pilot bracket.

2. Install the New Thermocouple

• Buy an exact replacement for the old thermocouple from a plumbing supply center that carries your brand or the plumber who installed your water heater.
• Push the tip of the new thermocouple into the pilot bracket clip as far as it will go.
• If there is a hexagonal nut at its tip, screw it to the bracket.
• Run the lead out and bend it up into a gentle curve.
• Screw the nut on the end of the thermocouple to the control unit by hand, then give it a quarter-turn with an open-end wrench.
• Relight the pilot (instructions for relighting a pilot on all major brands is here).
• If it does not stay lit, close the gas shutoff valve, and call for service.

Final Thoughts

A gas water heater thermocouple replacement is a project you can do yourself. But it is important that you follow the safety rules: (1) turn off the gas is priority number one, and (2) don’t touch the thermocouple until it has cooled down.

Related Resources

• Gas water heater troubleshooting guide
• A clear guide to the parts of a water heater
• How to relight your water heater pilot light (all major brands)
• How to replace an anode rod (if water rusty or smelly)
• 5 tips for preventing a leaking water heater disaster
• How long does a water heater last?
• Water heater repairs
• How to test your water heater’s T&P valve
• Does your water heater need a water softener?

Call 1-Tom-Plumber

Don’t hesitate to contact us here or call us at 1-Tom-Plumber (1-866-758-6237) if you need help safely maintaining, repairing, or replacing your gas water heater.

1-Tom-Plumber’s certified team of plumbers and drain technicians respond immediately to any emergency plumbing, drain cleaning, or water damage problem. We also handle the excavation of underground water lines and sewer main lines. Our immediate-response team is available every day and night of the year, even on holidays.