Water Heater Pilot Light Won't Stay Lit: The Real Fix

A pilot light usually fails to stay lit because a dirty, misaligned, or faulty thermocouple stops sending the small electrical signal that keeps the gas valve open. Cleaning it fixes many cases; replacing it fixes the rest — and it’s a cheap, common part.

Illustration of a gas water heater's pilot indicator glowing in a dim utility room. — Illustration of a gas water heater’s pilot indicator glowing in a dim utility room.

Likely Causes, Ranked

Dirty or sooty thermocouple
The most common cause — the small rod that sits in the pilot flame gets coated in soot over time.
Thermocouple not fully in the flame
Misalignment means it never heats enough to hold the valve open.
Insufficient hold time when lighting
Most units need the gas control knob held down 30 seconds to 2 minutes — releasing early is a common mistake.
Failed thermocouple
If cleaning and realigning don’t help, the part itself has likely failed.
Draft blowing out the pilot
Less common, but worth checking if the pilot goes out (rather than just failing to “hold”) right after lighting.

Step-by-Step Diagnosis

DIY SAFE
Follow the lighting instructions on the unit’s own label exactly

Hold the gas control knob down for the full time specified — releasing early is the single most common mistake.
DIY WITH CAUTION
If it lights but won’t stay lit, inspect the thermocouple

Look for soot or discoloration on the small metal rod near the pilot flame.
DIY WITH CAUTION
Clean the thermocouple gently with fine sandpaper or emery cloth

Same careful technique as cleaning a flame rod — don’t scratch through the sensing tip.
DIY WITH CAUTION
Confirm the thermocouple sits directly in the pilot flame

It needs to be bathed in flame, not just near it, to generate enough signal.
DIY WITH CAUTION
If cleaning and realignment don’t fix it, replace the thermocouple

It’s an inexpensive part and a common DIY repair for anyone comfortable with basic gas-appliance work — or a quick job for a plumber.

FAQ

How to clean a thermocouple?

Gently rub the sensing tip with fine sandpaper or emery cloth to remove soot, being careful not to bend or scratch through it.

Why does my pilot light go out as soon as I release the button?

The thermocouple isn’t generating enough signal to hold the gas valve open — usually because it’s dirty, misaligned, or simply worn out.

How do you know if your thermocouple is bad?

If cleaning it and confirming it’s properly positioned in the flame doesn’t fix the problem, the part itself has likely failed and needs replacing.

Will a pilot stay lit with a bad thermocouple?

No — a failed thermocouple is exactly why the gas valve closes and the pilot goes out shortly after you release the control knob.

Written by HotWater Decoded — water heater repair specialists. Technically reviewed by a licensed technician on our team.

Sources

Google’s AI Overview summary, a Reddit r/hvacadvice thread, and Lennox’s support page