Why won't my water heater pilot stay lit?

By Dana Whitlock. Updated October 2026. Repair or replace?

A pilot that lights and then dies is the gas control doing its job. The heater uses a small safety sensor in the flame to prove the pilot is burning, and if that proof is weak or missing, it shuts off the gas. The cause is usually the sensor wearing out, a dirty or weak pilot flame, a draft, or a combustion air problem. You can rule out a few outside factors yourself. The repair itself is gas work and belongs to a licensed plumber.

Likely causes

A worn flame sensor or thermocouple Pro job

The thermocouple (or a thermopile on some models) sits in the pilot flame and generates the tiny signal that holds the gas valve open. Years of heat wear it out. Swapping one involves the gas control and pilot assembly, so this is a job for a licensed plumber.

A dirty or weak pilot flame Pro job

Dust, lint or spider webs can clog the pilot orifice, leaving a small, yellow flame that cannot heat the sensor. Cleaning it means taking apart the burner compartment. Leave it to a technician.

Drafts or blocked combustion air Safe to check

A door left open to a windy garage, a box pushed against the base, or lint drawn in from a nearby dryer can starve or blow out the pilot. Modern tanks carry a flammable vapor resistant air intake screen at the bottom that can clog with dust. You can look for obvious blockages around the base without touching anything.

Gas supply problems Safe to check

A partly closed supply valve, low utility pressure, or an empty propane tank will starve the pilot. You can confirm the supply valve position and the propane gauge. Pressure testing is for the gas utility or a plumber.

The heater sensed flammable vapors Pro job

Many newer gas heaters have a safety system that locks out if it detects vapors from gasoline, paint or solvents stored nearby. Once tripped, some models need a technician to inspect and reset or replace parts.

Safe things to check first

• Confirm the gas supply valve on the pipe feeding the heater is fully open (handle parallel to the pipe). Look, do not adjust the heater's own control.
• On propane, check the tank gauge. A nearly empty tank can still feed a weak pilot.
• Clear storage away from the base and remove gasoline, paint thinner or solvents from the room.
• Close doors or windows that send a draft across the heater.
• Relight only per the instructions printed on the unit's label. A. O. Smith tells owners to wait 10 minutes between attempts, and if it fails after three tries, stop and call.

When to stop and call

Call a licensed plumber if the pilot goes out again within a day, if the label instructions fail after the stated number of tries, or if a status light flashes an error. Any smell of gas changes the plan entirely. Do not try to light anything, do not use switches, and leave the house. Phone the gas utility or 911 once you are outside.

Repair or replace?

Start with its age. Type the serial from the label:

A worn thermocouple on a young heater is a modest repair. Age matters more than the part. DOE puts the average gas storage heater at about 14.5 years, and a 2007 builders' survey listed gas water heaters at about 10 years. Date the unit with the age decoder above. Past 10 years, with rust at the base or rumbling too, a pilot repair is likely the first of several. Compare against the replacement range above before approving the work.