Water Heater Pilot Light Won't Stay Lit: Causes and Fixes
A pilot light that keeps going out is one of the most common gas water heater problems. Most causes are inexpensive to fix.
Safety Disclaimer
Water heater maintenance involves working with pressurized systems, scalding hot water, and potentially hazardous electrical or gas connections. Always shut off power (electric heaters) or gas supply (gas heaters) and allow water to cool to a safe temperature before beginning any maintenance. Wear appropriate safety equipment including gloves and eye protection. If you're uncomfortable with any step, contact a licensed plumber.
How the Pilot Light System Works
The pilot light is a small, continuously burning flame that ignites the main gas burner when the thermostat calls for heat. A thermocouple (a heat-sensing safety device) sits in the pilot flame. When the thermocouple detects heat, it keeps the gas valve open. If the pilot goes out, the thermocouple cools down and closes the gas valve, preventing gas leaks.
Cause 1: Dirty or Bent Thermocouple
The most common cause. If the thermocouple is coated in soot, carbon, or corrosion, it cannot sense the pilot flame properly and closes the gas valve.
Fix: Clean the thermocouple tip with fine sandpaper or steel wool. Ensure it is positioned directly in the pilot flame (the tip should be engulfed by the flame, not beside it). Bend it gently if needed.
For more on this topic, see our guide on Water Heater Pilot Light Won’t Stay Lit: Causes and Fixes.
Cost: Free (DIY).
For more on this topic, see our guide on Water Heater Repair: DIY Fixes vs. When to Call a Plumber.
Cause 2: Failed Thermocouple
Thermocouples wear out over time. If cleaning and repositioning does not solve the problem, the thermocouple has failed and needs replacement.
Fix: Replace the thermocouple. Universal thermocouples cost $10-$20 and are available at any hardware store. Unscrew the old one from the gas valve, remove it from the bracket, install the new one in reverse order.
Cost: $10-$20 (DIY) or $80-$150 (plumber).
Cause 3: Dirty Pilot Tube
The small tube that supplies gas to the pilot light can become clogged with dust, debris, or spider webs (yes, spiders love pilot tubes).
Fix: Turn off the gas. Use a thin needle or compressed air to clear the pilot tube orifice.
Cause 4: Drafts
Strong drafts near the water heater can blow out the pilot light. This is common in basements with open windows, garages, or near HVAC return vents.
Fix: Identify and eliminate the draft source. A draft hood on top of the heater should prevent most downdrafts.
Cause 5: Faulty Gas Valve
If the thermocouple, pilot tube, and draft are all ruled out, the gas control valve itself may be faulty.
Fix: This requires professional replacement. Gas valve replacement typically costs $200-$400 including parts and labor. On an older heater, this repair may not be cost-effective versus replacement.