Furnace starts normally but shuts down when the blower starts.
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.
Possible Causes
How to Fix / Troubleshooting
Safety first: This symptom can indicate a cracked heat exchanger and potential carbon monoxide risk. Install CO detectors and consider the furnace unsafe until inspected.
Steps to check:
- Observe flame: Through the sight glass, watch the burner flame as the blower starts. If the flame lifts, flickers violently, or is pulled away from the burner, shut down the furnace and call a technician.
- Check electrical connections: Tighten neutral and ground connections in the furnace junction box and on the control board.
- Clean flame sensor: Ensure the flame sensor is clean and properly positioned.
A licensed HVAC professional must inspect the heat exchanger and blower performance. Do not continue to operate the furnace until cleared.
Repair Difficulty
Required Part
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