Furnace Ignitor Not Glowing: Troubleshooting Guide
Quick answer
If your furnace ignitor isn't glowing, first check the power supply and thermostat settings. If those are fine, inspect the ignitor for cracks or damage and test the gas valve. Replace the ignitor if necessary.
Confirm the symptom
- Furnace fan runs but no heat
- No clicking or ignition sound
- Thermostat set to heat but no response
- Furnace makes noise but doesn't fire up
- Ignitor visible but doesn't glow when powered on
Tools and prep
- Multimeter — To test electrical components
- Screwdriver set — To access furnace panels
- Infrared thermometer — To check heat output
- Flashlight — To see inside the furnace
- Work gloves — For safety when handling hot parts
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Prep & safety
- Turn off the furnace power at the circuit breaker to prevent electrical shock.
- Allow the furnace to cool completely before inspection.
- Wear heat-resistant gloves to avoid burns from hot components.
- Ensure the gas supply is turned off before working on gas connections.
Step-by-step troubleshooting
Check Power Supply
Do: Verify the furnace is receiving power by checking the circuit breaker and wall switch.
Observe: Breaker is on and wall switch is in the 'on' position.
Means: Power is available to the furnace.
Next: Check Thermostat Settings
Check Thermostat Settings
Do: Ensure the thermostat is set to 'heat' and the temperature is set higher than room temperature.
Observe: Thermostat is set correctly and shows a call for heat.
Means: Thermostat is functioning properly.
Next: Inspect Ignitor
Inspect Ignitor
Do: Use a flashlight to look for cracks, damage, or carbon buildup on the ignitor.
Observe: Ignitor appears intact and clean.
Means: Ignitor may be working or needs cleaning.
Next: Test Ignitor Voltage
Test Ignitor Voltage
Do: Set the multimeter to AC voltage and test the ignitor's voltage when the furnace is calling for heat.
Observe: Voltage reading is within the manufacturer's specifications.
Means: Ignitor is receiving power.
Next: Check Gas Valve
Check Gas Valve
Do: Verify the gas valve is open and not blocked. Listen for a gas flow sound when the furnace starts.
Observe: Gas valve is open and gas flows when the furnace starts.
Means: Gas supply is available.
Next: Replace Ignitor if Necessary
Replace Ignitor if Necessary
Do: If the ignitor is damaged or not receiving power, replace it with a new one of the same model.
Observe: New ignitor glows when the furnace is powered on.
Means: Ignitor is functioning correctly.
Next: Test Furnace Operation
Common causes table
| Cause | Why | Likelihood | Difficulty | Part often needed |
|---|---|---|---|---|
| Faulty Ignitor | Cracks or carbon buildup prevent proper heating. | High | Medium | Yes |
| Low Voltage to Ignitor | Wiring issues or a failed control board prevent power delivery. | Medium | High | Yes |
| Blocked Gas Valve | Gas valve is closed or partially blocked, preventing fuel flow. | Medium | Low | No |
| Thermostat Issues | Incorrect settings or a faulty thermostat prevent heat call. | Low | Low | No |
| Dirty Air Filter | Restricted airflow can cause the furnace to shut down prematurely. | Low | Low | No |
| Failed Control Board | A malfunctioning control board fails to send power to the ignitor. | Low | High | Yes |
| Incorrect Ignitor Installation | Improper installation can prevent the ignitor from receiving power. | Low | Medium | Yes |
| Gas Supply Issues | Low gas pressure or a closed main gas valve prevents fuel delivery. | Low | Low | No |
Parts matching
When replacing the ignitor, ensure the new part matches the following specifications:
- Ignitor model: match the manufacturer and model number from the furnace label
- Voltage rating: ensure it matches the furnace's electrical requirements
- Length and shape: must fit the furnace's ignitor slot
- Material type: ceramic or silicon carbide as specified in the manual
Consult the furnace manual for exact part specifications and installation instructions.
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When to call a pro
- If the ignitor is damaged beyond cleaning or replacement
- If the control board shows signs of failure or error codes
- If gas supply issues persist after checking the main valve
- If you're unsure about electrical testing or component replacement
- If the furnace still doesn't ignite after replacing the ignitor
FAQ
How often should I replace my furnace ignitor?
Replace the ignitor every 5-7 years or if it shows signs of wear, cracks, or carbon buildup.
Can I clean the ignitor instead of replacing it?
Yes, gently clean the ignitor with a soft brush if it has minor dirt or debris. Avoid using harsh chemicals.
Why is my furnace making noise but not igniting?
Noise without ignition may indicate a faulty ignitor, gas valve issues, or a failed control board.
Is it safe to test the ignitor myself?
Testing the ignitor is safe if you follow proper safety precautions and turn off the power before inspection.