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DIY Troubleshooting Guide
How to Fix a Furnace That Won't Ignite
Safely troubleshoot a gas furnace that attempts to turn on but fails to produce heat.
DifficultyModerate
Est. Time⏱️ 20 minutes
Required ToolsFlashlight
1
1Step
Verify Gas Supply
Ensure the gas valve on the line feeding the furnace is fully in the "Open" position (parallel to the pipe) and that your home’s main gas service is active.
Context / Why
A furnace obviously cannot ignite without a steady supply of fuel.
2
2Step
Watch the Ignition Sequence
Turn the thermostat to Heat. Look through the small observation window on the furnace door. Note if the igniter glows orange but the flame fails to light.
Context / Why
Observing the sequence helps narrow down whether the issue is a bad igniter, a faulty gas valve, or a flame sensing problem.
3
3Step
Clean the Flame Sensor (If Needed)
Turn off the power, remove the sensor rod, gently clean it with fine steel wool, and reinstall.
Context / Why
A dirty flame sensor fails to detect the flame and will immediately shut down the furnace as a safety precaution.
Still experiencing issues?
If you completed the DIY steps and your system is still not functioning properly, it may require a professional diagnosis.
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