Fraser-Johnston
Flame Sensing Failure
Furnace starts but shuts off after a few seconds; burners light then go out repeatedly.
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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 or misaligned flame sensor, Poor burner ground, Low gas pressure, Cracked hot surface ignitor affecting flame pattern
How to Fix / Troubleshooting
Safety first: Turn off power and gas before accessing burners.
- Clean flame sensor: Remove and polish the flame sensor rod with fine steel wool. Reinstall in the same position so it is fully in the burner flame.
- Check burner flame: After reassembly, restore power and gas. Observe the flame through the sight glass. It should be steady and blue, contacting the flame sensor. Yellow or lifting flames indicate combustion issues requiring professional service.
- Verify ground: Ensure the burner assembly and IFC board ground wires are tight.
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Repair Difficulty
Medium
3/5
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