CODE 12
Fraser-Johnston
Flame Sense Low or Intermittent
LED flashes one short and two long blinks; furnace lights but shuts down intermittently.
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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, Low microamp flame signal, Loose flame sensor wiring
How to Fix / Troubleshooting
Safety first: Turn off power and gas before removing the burner access panel.
- Clean flame sensor: Remove the flame sensor from the burner assembly. Gently polish the rod with fine steel wool until shiny. Do not use sandpaper that leaves deep scratches. Reinstall and tighten the mounting screw.
- Check ground connections: Ensure the burner rack is firmly attached to the furnace chassis and that ground wires from the IFC board are secure.
- Inspect wiring: Follow the flame sensor wire back to the control board. Look for loose spade connectors or damaged insulation.
- Observe operation: Restore power and gas, then run the furnace. If burners still shut off after a few seconds, a technician should measure the flame signal in microamps and evaluate the sensor and control board.
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Repair Difficulty
Medium
3/5
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