- DIY difficulty
- Moderate
- Time
- 30–60 minutes
- Parts cost
- Thermocouple or OEM pilot assembly
- Pro price
- $215
Tools & materials
- Replacement thermocouple / pilot assembly (exact model)
- Open-end wrenches (7/16", 3/8")
- New inner-door gasket (sealed burners)
- Flashlight
- Multimeter (optional, for testing)
Symptoms of a failing thermocouple
- The pilot lights while you hold the button, then goes out when you release it.
- The pilot goes out at random, leaving no hot water.
- The status light on the gas valve flashes a pilot or flame-sense error code. Check the label on your valve. Look up your code: Rheem, Bradford White, A.O. Smith.
Before you buy parts, look at the pilot flame. It should be steady, blue, and wrap the tip of the thermocouple. A weak, yellow flame points to a dirty pilot orifice, not a bad thermocouple.
Which part does your heater use?
| Heater type | How to tell | Replace with |
|---|---|---|
| Older open burner | Removable outer and inner access doors, pilot visible | Universal or OEM thermocouple |
| Sealed combustion (FVIR) | Sealed inner door with a sight glass, push-button igniter | OEM pilot assembly (thermocouple, pilot and igniter) plus a new door gasket |
| Thermopile valve | Gas valve with a status LED and no 120V power | OEM thermopile |
How to replace a water heater thermocouple
- Turn the gas control to “Off” and close the gas shutoff valve on the supply line. Wait at least 10 minutes for the burner to cool.
- Remove the access doors. On sealed burners, unscrew the inner door carefully so you don’t tear the gasket.
- Disconnect the lines at the gas valve: the thermocouple nut, the pilot tube and the igniter wire.
- Slide out the burner assembly and remove the old thermocouple or pilot assembly.
- Install the new part. Thread the thermocouple nut into the valve by hand, then snug it about a quarter turn with a wrench. Don’t overtighten.
- Reinstall the burner, fit a new gasket if required, and refit the doors.
- Turn the gas back on and relight, following the lighting instructions on the heater’s label. Leak-test the pilot tube fitting with soapy water. Bubbles mean a leak.
When to call a pro
- A new thermocouple didn’t fix it. Work through our pilot light troubleshooter. The gas control valve may be failing.
- You see scorching around the burner door, or the heater has a tripped flammable-vapor sensor.
- You’re not comfortable working on gas connections.
A fair price for a pro thermocouple or pilot assembly replacement is about $215, including a pilot cleaning and a gas leak test.
Frequently asked questions
How do I know if my water heater thermocouple is bad?
The pilot lights while you hold the pilot button but goes out as soon as you let go. That usually means the thermocouple (or thermopile) isn’t producing enough voltage to hold the gas valve open. A dirty pilot or a bad gas valve can cause the same symptom.
What is the difference between a thermocouple and a thermopile?
A thermocouple makes a small voltage that holds the gas valve’s safety magnet open. A thermopile is a bundle of thermocouples that makes more voltage, enough to power the whole valve on many newer heaters. They aren’t interchangeable. Replace like with like.
Can I use a universal thermocouple?
On older open-burner heaters, often yes. Most heaters built in the last two decades use sealed combustion chambers (FVIR) with a manufacturer pilot assembly, and those should get the OEM part, plus a new inner door gasket.
Does a propane water heater use the same thermocouple?
The thermocouple itself is often similar, but the pilot assembly and orifice are specific to propane (LP) or natural gas. Always order parts for your heater’s exact model and gas type.