Furnace pilot light won't stay lit

Symptoms

• Pilot lights but goes out within seconds of releasing the knob
• Repeated relighting doesn't help
• No heat because the pilot keeps dying

Likely causes

• CommonDirty or misaligned thermocoupleThis safety sensor must sit directly in the pilot flame to register it and keep gas flowing.
• CommonWeak or failing thermocoupleThermocouples wear out over years and stop holding the valve open even when clean.
• PossibleDraft blowing out the pilot flameAirflow from a nearby vent or door can extinguish a small pilot flame.
• PossibleDirty pilot orifice restricting gas flowA partially clogged orifice produces a weak flame that won't heat the thermocouple enough.
• Less commonFaulty gas valveThe valve itself can fail and stop supplying gas properly to the pilot.

What to do

1. Turn the gas control knob to Off and wait 5 minutes for gas to clear before doing anything else.
2. Follow the lighting instructions printed on the furnace panel exactly, holding the pilot knob in as directed.
3. Hold the knob in for the full time listed (often 30–60 seconds) before releasing so the thermocouple heats fully.
4. If it goes out immediately when released, the thermocouple is likely dirty; let it cool and gently clean it with fine sandpaper or a cloth.
5. Check that the thermocouple tip sits directly in the blue part of the pilot flame, not off to the side.
6. If cleaning doesn't help, the thermocouple has likely failed and needs replacement, which is an inexpensive part.
7. Never bypass the thermocouple or hold the gas valve open manually to force the pilot to stay lit.

Tools and parts

• Fine sandpaper or emery cloth
• Flashlight

When to call a pro

Call a technician or your gas utility if the pilot still won't hold after cleaning the thermocouple, or if you ever smell gas.

Safety