How To Replace A Water Heater Thermocouple

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How to Replace a Water Heater Thermocouple

Total Time:An hour or lessComplexity:BeginnerCost:Less than $20

By Family Handyman

Family Handyman's Editorial Process

Updated on Jan. 24, 2025

Save your hot water heater with a new thermocouple!

Time

An hour or less

Complexity

Beginner

Cost

Less than $20

Introduction

A hot water heater that doesn't heat might just need a new thermocouple. Signs of a bad one include difficulty keeping the pilot light lit or having no hot water despite the gas being on. It’s also a good place to start troubleshooting, since it’s an inexpensive part and relatively straightforward process for someone with basic DIY skills. “It involves shutting off the gas, removing the burner assembly, replacing the thermocouple and reassembling the unit,” says Pete Duncanson, vice president of training and development at ServiceMaster Restore. “However, if you’re unsure or uncomfortable working with gas lines, it’s better to call a professional.” If you suspect your thermocouple might have gone bad, here is how to replace the part and keep your hot water heater working for years to come.

Replace a Thermocouple to Fix a Pilot Light

The No. 1 cause of pilot lights that won’t stay lit is a worn-out thermocouple. It’s easy to replace, and a new one costs $5 to $10. Rather than trying to unfasten the thermocouple inside the water heater’s burning chamber, it’s easier to remove the whole burner and thermocouple assembly. Then, detach the thermocouple from the burner and take it with you to the home center or hardware store to ensure you buy the right replacement.

First, shut off the gas valve on the water heater and the gas valve on the gas line near the heater. Then unfasten the three nuts that hold the thermocouple and the two gas tubes to the valve.

Tools Required

• Adjustable wrench
• Wrench set

Materials Required

• Replacement thermocouple

Project step-by-step (3)

Step 1

Unscrew the thermocouple lead along with the two gas tubes.

Water Heater Maintenance: Extend Water Heater Life Step 2

Burner assembly

The burner typically sits loosely—or under clips—in the burning chamber and just slides out.

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Vacuum

This is a good time to vacuum out the burner compartment, check for water leaks and remove debris in the burner ports. Attach the thermocouple and reinstall the burner assembly. Light the pilot following the instructions on the water heater. Check for gas leaks by applying soapy water to joints and looking for bubbles while the main burner is firing.

Troubleshooting Common Water Heater Repairs

Learn how to troubleshoot and fix common water heater problems, from pilot light issues to leaks, with simple step-by-step solutions and maintenance tips.

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• How to Dispose of a Water Heater
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• Water Heater Leaking from Drain Valve? Here’s What to Do
• A Water Heater Vent Installed Like This Can Have Lethal Consequences
• How to Fix a Water Heater Pilot Light
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• Is Your Water Heater’s TPR Valve Leaking? Here’s What to Do
• Water Heater Anode Rod Replacement
• Top Water Heater Brands

FAQ

What is a water heater thermocouple?

A water heater thermocouple is a safety device that detects whether the pilot light is on in a gas water heater.

“If the pilot light goes out, the thermocouple shuts off the gas supply to prevent leaks, a critical safety feature,” says Myles Robinson, home expert at UK Composite Doors. “You’ll know the thermocouple might be bad if the pilot light won’t stay lit or you have trouble igniting it in the first place.”

Does replacing a thermocouple improve water heater performance?

No, a thermocouple doesn’t technically improve performance, but a water heater won’t work without one.

“Replacing a thermocouple restores functionality to the water heater by ensuring the pilot light stays lit,” says Duncanson. “While it doesn’t directly improve performance, it’s essential for the heater to operate safely and effectively.

About the Experts

• Myles Robinson is a home expert, founder at UK Composite Doors and previously owned and operated Boiler Central, a multi-million dollar boiler repair business.
• Pete Duncanson is vice president of training and development at ServiceMaster Restore, where he has worked since 1995.