Day & Night
Flame Sensing Failure
Furnace starts then shuts down after a few seconds; burners light but go out quickly.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Dirty flame sensor, poor burner ground, reversed line polarity, weak flame signal due to low gas pressure
How to Fix / Troubleshooting
Safety first: Turn off power and gas before servicing.
- Clean flame sensor: Remove the flame sensor and gently clean the rod with fine abrasive pad until shiny. Reinstall and reconnect the wire.
- Check ground and polarity: Ensure the furnace is properly grounded and that hot and neutral are correctly wired at the service switch or outlet.
- Inspect burners: Clean burner ports of rust and debris to ensure a strong, even flame that engulfs the flame sensor.
If the problem persists, a technician should measure flame rectification current and gas pressure.
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Repair Difficulty
Medium
3/5
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