05
American Standard
Flame Sensed But Lost During Run
Error code 05 and furnace starts then shuts down after a few seconds of flame
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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 mispositioned flame sensor, Poor burner ground or loose ground wire to burner rack, Low gas pressure causing unstable flame, Cracked heat exchanger causing flame disturbance
How to Fix / Troubleshooting
Safety: Turn off power and gas before servicing burners or flame sensor.
Error 05 indicates the control board senses flame initially but then loses the signal.
- Clean and reposition flame sensor:
- Remove the flame sensor and clean the rod with fine abrasive pad.
- Ensure the sensor tip is directly in the burner flame path when reinstalled.
- Check grounding:
- Verify the green ground wire from the control board is securely attached to the furnace chassis.
- Ensure burner rack screws are tight and free of rust, providing a solid ground path.
- Inspect burner flame:
- With the front panel in place and viewing through the sight glass, observe flame color and stability.
- Flames should be mostly blue and steady. Yellow tipping or lifting indicates combustion issues that require professional adjustment.
- If flame dropout persists, have a licensed technician check gas pressure, burner alignment, and inspect the heat exchanger for cracks.
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Repair Difficulty
Hard
4/5
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