Pilot Light on Furnace Not Igniting

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Quick answer
Confirm the symptom
Tools and prep
Step-by-step troubleshooting
Common causes table
Parts matching
When to call a pro
FAQ
Related guides

Quick answer

Turn off the furnace power and gas. Locate the pilot light assembly, press and hold the reset button while lighting the pilot with a long match or lighter. If it won't stay lit, the thermocouple or gas valve may need adjustment or replacement.

Confirm the symptom

Furnace does not produce heat.
Pilot light is out or won't stay lit.
No gas smell when attempting to light the pilot.
Reset button on the gas valve is depressed or damaged.

Tools and prep

Long-reach lighter or long match
Screwdriver (flathead or Phillips, depending on furnace model)
Owner's manual for your furnace
Disposable gloves
Turn off power to the furnace at the circuit breaker.
Turn off the gas supply to the furnace.

Step-by-step troubleshooting

Check Gas Supply
Do: Verify the gas valve is fully open and there's no gas leak smell.
Observe: Gas valve is open, no gas odor detected.
Means: Gas supply is available and safe to proceed.
Next: Step 2
Access Pilot Light
Do: Remove the furnace access panel to locate the pilot light assembly and gas valve.
Observe: Pilot light assembly is visible and accessible.
Means: You can safely attempt to light the pilot.
Next: Step 3
Reset the Gas Valve
Do: Press and hold the reset button on the gas valve for 30 seconds.
Observe: Reset button stays depressed after releasing.
Means: Gas valve is reset and ready for ignition.
Next: Step 4
Light the Pilot
Do: While holding the reset button, use a long match or lighter to ignite the pilot light.
Observe: Pilot light ignites and stays lit while holding the button.
Means: Pilot is lit, but needs to stay lit after release.
Next: Step 5
Hold for Thermocouple
Do: Continue holding the reset button for 30–60 seconds to allow the thermocouple to heat up.
Observe: Pilot light remains lit after releasing the button.
Means: Thermocouple is functioning correctly.
Next: Step 6
Test Ignition
Do: Release the reset button and check if the pilot light stays on.
Observe: Pilot light remains lit.
Means: Pilot light is successfully ignited and stable.
Next: Done
Troubleshoot Further
Do: If the pilot light goes out, repeat the lighting process or check for blockages in the pilot tube.
Observe: Pilot light still won't stay lit.
Means: Possible issue with thermocouple, gas valve, or airflow.
Next: Contact a professional

Common causes

Cause	Likelihood	Difficulty	Part often needed
Thermocouple Failure The thermocouple senses the pilot flame and sends a signal to the gas valve to keep the gas flowing. If it's faulty, the gas will cut off.	Common	Easy–Medium	Thermocouple
Dirty or Clogged Pilot Tube Dust or debris can block the gas flow to the pilot light, preventing ignition.	Common	Easy	None (cleaning usually suffices)
Gas Valve Issues A faulty gas valve may not allow gas to flow to the pilot or main burners.	Sometimes	Hard	Gas valve assembly
Low Gas Pressure Insufficient gas pressure can prevent the pilot from staying lit.	Sometimes	Hard	Gas pressure regulator
Faulty Igniter or Spark Generator In some furnaces, an electronic igniter or spark generator is used to light the pilot. If it's defective, the pilot won't ignite.	Sometimes	Medium	Igniter or spark generator
Air in Gas Line Air trapped in the gas line can prevent gas from reaching the pilot light.	Rare	Medium	None (purging gas line usually fixes)
Incorrect Pilot Adjustment If the pilot flame is too small or not positioned correctly, it may not heat the thermocouple enough.	Sometimes	Easy	None (adjustment usually fixes)

Parts matching

Common parts needed for pilot light issues include:

Thermocouple – senses pilot flame and controls gas flow
Gas valve assembly – regulates gas to the pilot and burners
Igniter or spark generator – creates spark for pilot ignition
Gas pressure regulator – maintains proper gas pressure
Pilot light assembly – includes pilot tube and orifice

Always refer to your furnace's owner's manual to confirm the correct part numbers and compatibility.

When to call a professional

You smell gas after multiple attempts to light the pilot.
The pilot light won't stay lit despite following all steps.
You hear a hissing sound from the gas valve, indicating a gas leak.
You're unsure about the cause or uncomfortable working with gas appliances.
The furnace is older than 15 years and has recurring pilot light issues.

FAQ

How do I know if the thermocouple is bad?

If the pilot light goes out when you release the reset button, the thermocouple is likely faulty. It may need to be cleaned or replaced.

Can I relight the pilot light multiple times if it goes out?

Yes, but if it goes out repeatedly, stop and check for blockages or a faulty thermocouple. Don't exceed 5 attempts to avoid gas buildup.

Why does my pilot light go out when I release the reset button?

This usually means the thermocouple isn't heating properly, the pilot flame is too small, or there's a gas flow issue.

Is it safe to light the pilot light myself?

Yes, if you follow the manufacturer's instructions and take proper safety precautions. If you're unsure, call a professional.

Can a dirty air filter cause the pilot light to go out?

Not directly, but a dirty filter can restrict airflow and affect furnace performance. Always keep filters clean for optimal operation.