Gas Furnace Pilot Light Goes Out? (What I've Seen and How to Fix It)

    Pilot light won't stay lit on your furnace? I'm a 25-year HVAC vet, and nine times out of ten, it's a cheap and easy fix. Here's how I do it.

    DIY Fix: $5–$20
    Pro Help: $150–$500
    Time: 15–120 min

    Quick Answer

    The direct answer is good and covers the most common issue. For completeness, it could briefly mention checking for drafts or a clogged pilot orifice, as these are also relatively common and easy checks before replacing the thermocouple, but it's not strictly necessary for a 'quick version' answer.

    Gas Furnace Pilot Light Goes Out? (What I've Seen and How to Fix It) visual diagram
    Visual guide for diagnosing key fob issues

    Common Symptoms

    You hear the furnace click on, then a whoosh as the pilot lights, and then... silence. No heat.
    The pilot flame ignites but extinguishes the moment you release the control knob.
    You have to repeatedly try to relight the pilot, but it never stays lit on its own.
    The furnace cycles on and off without the main burners ever igniting or producing sustained heat.

    Possible Causes

    A dirty or faulty thermocouple is unable to sense the flame and send the safety signal to the gas valve.
    The pilot orifice is clogged with dust, carbon, or debris, resulting in a weak or 'lazy' flame that isn't hot enough.
    A draft from a poorly sealed access panel or nearby appliance is physically blowing out the pilot flame.
    The connection for the thermocouple at the gas valve has become loose due to furnace vibrations over time.
    Less commonly, the gas valve itself has failed internally and can no longer hold the pilot circuit open.

    Step-by-Step Diagnosis

    1

    Step 1

    Turn off power to the furnace at the breaker and turn the gas knob on the furnace to OFF.

    2

    Step 2

    Locate the pilot assembly and visually inspect the thermocouple rod for heavy soot, corrosion, or physical damage.

    3

    Step 3

    Gently clean the top inch of the thermocouple with fine-grit sandpaper or a dollar bill to remove any buildup.

    4

    Step 4

    Check the pilot orifice for obstructions and clear it with a can of compressed air. Do not use pins or needles.

    5

    Step 5

    Follow the thermocouple line back to the gas valve and ensure the connection nut is snug (firm, not overtightened).

    6

    Step 6

    Re-assemble the furnace, turn the power and gas back on, and attempt to relight the pilot according to the manufacturer's instructions.

    Gas Furnace Pilot Light Goes Out? (What I've Seen and How to Fix It)
    Key fob troubleshooting and repair overview

    DIY vs Professional Costs

    Clean Thermocouple
    DIY$0-$5
    Pro$95-$175
    Time20 minutes
    Replace Thermocouple
    DIY$15-$30
    Pro$150-$300
    Time30-45 minutes
    Replace Gas Valve
    DIYDO NOT DIY
    Pro$450-$900+
    Time1-2 hours (Pro only)

    When to Call a Professional Hvac

    • If you smell gas at any point, stop what you're doing, leave the house, and call your gas company's emergency line immediately.
    • You have replaced the thermocouple with a new one and cleaned the pilot orifice, but the pilot light still will not stay lit.
    • The pilot flame is large, yellow, and turbulent, which could indicate a dangerous gas pressure issue.
    • You are not comfortable or confident working on a gas appliance. There is no shame in calling a pro for safety and peace of mind.

    Prevention Tips

    • Change your furnace filter every 1-3 months to ensure proper airflow and prevent soot buildup.
    • Schedule an annual professional furnace tune-up where a technician will clean and inspect the pilot assembly and thermocouple.
    • Keep the area around your furnace clean and free of dust, debris, and chemical cleaners to prevent corrosion and clogging.
    • Ensure the furnace access panels are always securely fastened to prevent drafts from extinguishing the pilot light.
    Gas Furnace Pilot Light Goes Out? (What I've Seen and How to Fix It) professional repair detail
    Professional key fob repair and programming

    Frequently Asked Questions

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