Furnace Not Igniting No Gas

Quick answer

If your furnace isn't igniting and there's no gas smell, first check the gas supply valve and emergency shutoff. Ensure the pilot light is lit, and verify the thermocouple is functioning. If these steps don't resolve the issue, contact a professional HVAC technician.

Confirm the symptom

• Furnace does not ignite at all
• No gas smell when attempting to start furnace
• Pilot light is out or won't stay lit
• Thermostat is set to heat but furnace does not respond

Tools and prep

• Screwdriver (flathead and Phillips)
• Flashlight
• Gas leak detector or soapy water solution
• Owner's manual for your furnace
• Disposable gloves and safety goggles
• Ensure the area is well-ventilated

Step-by-step troubleshooting

1. Check Gas Supply
   Do: Locate the gas supply valve near the furnace and ensure it is fully open.
   Observe: Gas valve is open and not obstructed.
   Means: Gas supply is not the issue if the valve is open.
   Next: Check for gas flow using a gas leak detector or soapy water on connections.
2. Check Emergency Shutoff Valve
   Do: Look for an emergency gas shutoff valve near the furnace and ensure it is in the 'on' position.
   Observe: Shutoff valve is fully open with no signs of tampering.
   Means: If closed, gas won't reach the furnace.
   Next: If closed, turn it on and attempt to relight the pilot light.
3. Inspect Pilot Light
   Do: Look at the pilot light assembly to see if it is lit.
   Observe: Pilot light is either lit or unlit.
   Means: An unlit pilot light prevents ignition.
   Next: If unlit, follow manufacturer instructions to relight it.
4. Test Thermocouple
   Do: Use a multimeter to test the thermocouple for proper voltage output when the pilot is lit.
   Observe: Voltage reading should be between 20–30 millivolts.
   Means: Low or no voltage indicates a faulty thermocouple.
   Next: Replace the thermocouple if it's faulty.
5. Check Gas Valve Solenoid
   Do: Inspect the gas valve solenoid for damage or wear.
   Observe: Solenoid shows no visible damage and is securely connected.
   Means: A faulty solenoid can prevent gas flow.
   Next: Replace the gas valve if the solenoid is damaged.
6. Inspect Pressure Switch
   Do: Check the pressure switch for proper operation and connections.
   Observe: Pressure switch is closed and connected properly.
   Means: A faulty pressure switch can prevent gas flow.
   Next: Replace the pressure switch if it's faulty.
7. Check for Gas Leaks
   Do: Apply soapy water to gas connections and look for bubbles.
   Observe: No bubbles form on connections.
   Means: Bubbles indicate a gas leak, which is dangerous.
   Next: Turn off gas supply immediately and call a professional.

Common causes

Parts matching

Common parts needed for a furnace not igniting with no gas include:

• Thermocouple
• Gas Valve Assembly
• Pressure Switch
• Gas Line Repair Kit

Always match parts to your furnace model and consult the owner's manual for compatibility.

When to call a professional

• If you detect a gas leak (smell or bubbles from soapy water)
• If the pilot light won't stay lit after multiple attempts
• If the furnace still doesn't ignite after checking all basic components
• If you're unsure about any step or lack the proper tools
• If the furnace is old and requires major repairs

FAQ

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