Pilot Light Won't Stay Lit

If you have a standing-pilot gas furnace (mostly 1990s and older), the pilot light stays lit continuously and provides the flame that ignites the main burner when the thermostat calls for heat. When the pilot won't stay lit, no main burner ignition can happen — no heat. Modern furnaces (roughly 2000+) use hot-surface igniters and don't have pilot lights, so if your furnace is newer than 2000, see our furnace won't ignite guide instead.

Most Likely Causes

1. Failed thermocouple (most common)

The thermocouple is a small metal rod tip that sits in the pilot flame and generates a tiny voltage that tells the gas valve 'the pilot is lit, it's safe to keep gas flowing to the pilot.' When the thermocouple weakens with age (typical life 5-8 years), it can't generate enough voltage — the gas valve shuts the pilot off within 30 seconds of you releasing the pilot button. Fix: replace thermocouple, $80-$160 including labor.

2. Dirty or clogged pilot orifice

Dust, spider webs, or corrosion in the pilot orifice can produce a weak, yellow, or flickering flame that doesn't properly heat the thermocouple. Result: pilot lights but goes out. A cleaning restores it.

3. Draft blowing the pilot out

Downdraft in the flue, a nearby door being opened repeatedly, or a fan blowing air across the furnace closet can extinguish the pilot. Investigate whether pilot outages coincide with wind or door activity.

4. Failed gas valve

The gas valve itself controls both the pilot and main burner gas flow. If the pilot section of the valve fails, the pilot may light momentarily but the valve won't hold it open. Replacement runs $420-$640.

5. Interrupted gas supply

If the gas is off at the main shutoff, a nearby valve was closed, or you're on propane and the tank ran low, the pilot won't stay lit for a lack of fuel. Verify your gas service is on — check by lighting a stove burner.

Try These Steps Before You Call

• Safety first: If you smell gas near the furnace, do NOT attempt to relight. Leave the house, call your gas utility from outside, then call us.
• Locate the pilot light and gas valve at the base of the furnace. There's usually a diagram on the door.
• Set the gas valve knob to 'OFF' and wait 5 minutes for any residual gas to clear.
• Set the valve to 'PILOT', press and hold the reset button, and light the pilot with a long lighter or match.
• Hold the reset button down for a full 60 seconds after the pilot lights — this gives the thermocouple time to heat up.
• Release the reset button. If the pilot immediately goes out, the thermocouple has failed — call us.
• If the pilot stays lit, turn the valve to 'ON' and set the thermostat to call for heat.
• If the pilot lights but the flame is yellow, weak, or flickering, the pilot orifice needs cleaning.

Other Common Heating Problems

See also: AC problems