Water Heater Pilot Light Won't Stay Lit? Here's Why

If you wake up to a cold shower and find the pilot light out on your gas water heater, relighting it is usually the first step. But if it lights and then goes out again, or will not stay on at all, something is preventing the burner's safety system from staying open. These systems are designed to shut off gas whenever they are unsure the flame is present, so the cause is usually a sensor or a dirty part rather than a dangerous condition.

Before anything else: smell for gas

Natural gas and propane carry an added odorant that smells like rotten eggs. If you notice that smell near the water heater, do not try to relight anything, do not flip light switches, and leave the house. Call your gas utility or propane supplier from outside.

1. A worn thermocouple

The thermocouple is a thin copper rod that sits in the pilot flame. When heated, it produces a tiny electrical signal that tells the gas valve the pilot is lit. Over time it wears out, or the pilot flame shifts so it no longer touches the tip. If the pilot stays lit only while you hold down the button, the thermocouple is the most likely culprit. It is an inexpensive part and a common repair.

2. A dirty pilot tube

Dust, lint, and spider webs can partially block the small pilot opening. The flame becomes weak, yellow, or flickering instead of a crisp blue, and it does not heat the thermocouple properly. Garage-installed heaters in Central Florida are especially prone to dust and insects. Cleaning the pilot assembly often restores a strong flame.

3. A clogged flame arrestor screen

Gas water heaters made in recent decades include a flammable vapor ignition resistant (FVIR) design with a screen at the bottom of the combustion chamber. Lint and dust clog this screen and starve the burner of air, which can snuff out the pilot. Some models also have a thermal cutoff that trips when it senses overheating. Never bypass these safety features. Cleaning the screen or resetting the system properly is a job for a qualified technician on many models.

Other possible causes

• •A failing gas control valve that does not hold open even with a good thermocouple signal.
• •Low gas supply, such as a nearly empty propane tank or a partially closed shutoff valve.
• •Downdrafts through the vent, especially on windy days or when bathroom exhaust fans pull air from the space.
• •A kinked or loose thermocouple connection at the gas valve.

When to call a plumber

Call if you have replaced the thermocouple and the problem continues, if the pilot flame is yellow or lazy after cleaning, if the thermal cutoff keeps tripping, or if you see scorching around the burner access. Those point to combustion or venting problems that should be diagnosed by someone licensed for gas work.

• Water heater service
• What to do if you smell gas
• Gas piping service