Start here: does it light at all?
- It lights but goes out when you release the pilot button: this is almost always the thermocouple or thermopile. Start at step 3.
- It stays lit for minutes or hours, then goes out: suspect airflow (step 4), drafts (step 5) or venting (step 6).
- It won’t light at all: check that the gas supply valve is open and other gas appliances work, then check for a tripped flammable-vapor sensor (step 7).
Troubleshoot step by step
- Relight correctly. Follow the lighting instructions on the heater’s label exactly, including holding the pilot button for the full time it states (often 30–60 seconds) after the pilot lights.
- Look at the flame. A healthy pilot is steady and mostly blue, and it wraps the top of the thermocouple. A small, yellow or lazy flame points to a dirty pilot orifice or low airflow.
- Check the thermocouple. Make sure it’s firmly connected at the gas valve (snug, not overtightened) and that its tip sits in the flame. If it’s more than a few years old, replacing it is cheap and fixes most cases. See our thermocouple guide.
- Clean the air intake screen. On sealed-burner heaters there’s a screen or flame arrestor around the base. Vacuum lint, dust and pet hair from it with the heater off. A clogged screen is a very common, often-missed cause.
- Stop drafts. Open windows, fans, dryer exhaust or a garage door near the heater can blow out a weak pilot. Make sure the outer burner door is in place.
- Check the venting. With the burner running, the flue should draw. A blocked chimney or a disconnected vent pipe can starve the flame or cause backdrafting. This is a carbon monoxide risk, so call a pro if you suspect it.
- Check for a vapor-sensor lockout. If the heater won’t relight and shows a lockout code on the status light, the flammable-vapor sensor may have tripped. Remove any gasoline, paint or solvents stored nearby. Resetting usually needs a pro or replacement parts. Look up your code: Rheem, Bradford White, A.O. Smith.
Causes at a glance
| Cause | Clue | Fix | Pro price |
|---|---|---|---|
| Worn thermocouple / thermopile | Goes out when you release the button | Replace it (DIY-friendly) | $215 |
| Dirty pilot orifice | Small, yellow, weak flame | Clean the pilot assembly | $215 |
| Clogged air intake screen | Goes out after running a while | Vacuum the screen | — |
| Drafts | Goes out at random | Block the draft, refit the door | — |
| Venting problem | Soot, scorch marks, CO alarm | Call a pro now | — |
| Failing gas control valve | New thermocouple didn’t help | Replace the valve | $450 |
When to call a pro, or replace the heater
Call a pro if you see soot or scorch marks, smell gas, your CO alarm sounds, or a new thermocouple didn’t fix it. If the heater is 10 or more years old and needs a gas valve, compare that cost with a new water heater. Not sure how old yours is? Look up its age by serial number.
Frequently asked questions
Why does my water heater pilot light keep going out?
The most common causes are a weak or failing thermocouple (or thermopile), a dirty pilot orifice that makes a small, weak flame, and a clogged air intake screen on sealed-burner heaters that starves the flame of air. Drafts, a tripped flammable-vapor sensor and a failing gas control valve are less common causes.
My pilot still goes out after a new thermocouple. What now?
Check the pilot flame (it should be steady, blue and wrap the thermocouple tip), clean the air intake screen at the bottom of the heater, and look for drafts or venting problems. If those are fine, the gas control valve may not be holding the thermocouple signal, which is a job for a pro.
Is it dangerous if the water heater pilot keeps going out?
The gas control shuts off the gas when the pilot goes out, so it isn’t usually dangerous by itself. But if you smell gas, see scorch marks around the burner door, or your CO alarm sounds, leave the house and call your gas utility.
Can a dirty air intake screen make the pilot go out?
Yes. Most gas water heaters built since the mid-2000s have sealed combustion chambers with a screen or flame arrestor at the bottom. Lint, dust and pet hair can clog it, which starves the burner of air so the pilot weakens and goes out.