Quick answer
If your furnace pilot light keeps blowing out, check the thermocouple alignment and gas pressure. Ensure the area is clean and free of drafts. If the issue persists, replace the thermocouple or call a professional.
Confirm the symptom
- Pilot light goes out after igniting
- Pilot light flickers or burns unevenly
- Furnace fails to start after lighting the pilot
- Pilot light goes out when you release the control knob
- You hear a hissing sound near the pilot light
Tools and prep
- Screwdriver (flathead or Phillips, depending on furnace model)
- Lighter or matches
- Owner's manual for your furnace model
- Safety glasses
- Turn off power to the furnace at the circuit breaker
- Ensure the gas supply is on but the furnace is off before troubleshooting
Step-by-step troubleshooting
- Locate and Access the Pilot LightDo: Find the access panel near the bottom of the furnace and remove it to expose the pilot light assembly.Observe: You should see the pilot light tube and thermocouple.Means: You've accessed the correct area for troubleshooting.Next: Check for dirt or debris around the pilot light and thermocouple.
- Clean the Pilot Light and ThermocoupleDo: Use a soft brush or cloth to gently remove any dirt, dust, or debris from the pilot light and thermocouple.Observe: The pilot light and thermocouple should be clean and free of blockages.Means: A clean pilot light and thermocouple can ignite and stay lit properly.Next: Relight the pilot light and observe if it stays lit.
- Relight the Pilot LightDo: Press the reset button on the gas valve, light the pilot with a lighter or match, and hold the reset button for 20–30 seconds.Observe: The pilot light should stay lit after releasing the button.Means: The pilot light is functioning correctly if it remains lit.Next: If the pilot light goes out again, check the thermocouple alignment.
- Check Thermocouple AlignmentDo: Ensure the thermocouple is positioned so it is in the pilot light's flame and not touching the burner.Observe: The thermocouple should be in the blue cone of the pilot flame.Means: Proper alignment allows the thermocouple to generate enough voltage to keep the gas valve open.Next: If misaligned, adjust it carefully and relight the pilot light.
- Test Gas PressureDo: Use a manometer if available to check the gas pressure at the furnace. Refer to the manufacturer's specifications for the correct pressure range.Observe: Gas pressure should be within the recommended range specified in the manual.Means: Incorrect gas pressure can cause the pilot light to go out.Next: If pressure is low, contact a professional to adjust it.
- Check for Drafts or Air LeaksDo: Inspect the area around the furnace for any drafts, open vents, or air leaks that could be blowing out the pilot light.Observe: No noticeable drafts or air movement near the furnace.Means: Drafts can extinguish the pilot light or prevent it from staying lit.Next: Seal any leaks or adjust vents to eliminate drafts.
Common causes
| Cause | Likelihood | Difficulty | Part often needed |
|---|---|---|---|
| Misaligned Thermocouple If the thermocouple is not positioned correctly in the pilot flame, it won't generate enough voltage to keep the gas valve open. | Common | Easy | Thermocouple |
| Dirty Pilot Light or Thermocouple Dust or debris can block the pilot flame or prevent the thermocouple from sensing heat properly. | Common | Easy | None (cleaning required) |
| Low Gas Pressure Insufficient gas pressure can result in a weak pilot flame that easily goes out. | Sometimes | Hard | Gas pressure adjustment by a professional |
| Drafts or Air Leaks Air movement near the furnace can blow out the pilot light or prevent it from staying lit. | Sometimes | Easy–Medium | Sealant or vent adjustment |
| Faulty Gas Valve A malfunctioning gas valve may not supply enough gas to keep the pilot lit or may close prematurely. | Rare | Hard | Gas valve replacement |
| Failed Thermocouple Over time, thermocouples can wear out and fail to generate the necessary voltage to keep the gas valve open. | Sometimes | Easy | Thermocouple |
Parts matching
Common parts needed for a pilot light issue include:
- Thermocouple – Replaces the part that senses the pilot flame and keeps the gas valve open
- Gas valve – Controls the gas flow to the pilot and burners
- Manometer – For measuring gas pressure if you suspect low pressure
- Sealant or caulk – For sealing air leaks around the furnace area
Always purchase parts that are compatible with your furnace model. Refer to your owner's manual for specifications.
When to call a professional
- The pilot light continues to go out after cleaning and realignment
- You suspect low gas pressure and don't have a manometer
- You smell gas or hear a hissing sound near the furnace
- You're unsure about any step in the process or feel unsafe working on the furnace
- The furnace still doesn't operate correctly after attempting all troubleshooting steps
FAQ
How do I know if the thermocouple is faulty?
If the pilot light goes out when you release the reset button, the thermocouple may not be generating enough voltage. Try cleaning it first, and if the issue persists, replace it.
Can a dirty filter cause the pilot light to go out?
A dirty air filter can restrict airflow and affect furnace performance, but it typically doesn't directly cause the pilot light to go out. However, poor airflow can contribute to other issues that might indirectly affect the pilot light.
Is it safe to relight the pilot light multiple times?
Yes, it's generally safe to relight the pilot light a few times. However, if it continues to go out, stop and investigate the cause to avoid potential gas buildup.
What should I do if I smell gas?
Immediately shut off the gas supply, open windows for ventilation, and contact a professional HVAC technician or your gas company. Do not attempt to relight the pilot light or use any electrical devices.