Furnace starts normally but shuts off when the blower comes on, then tries again.
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
Critical safety: This symptom can indicate a cracked heat exchanger and potential carbon monoxide risk. Install a CO detector if you do not have one and consider the furnace unsafe until inspected.
Steps to check (visual only):
- 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 off the furnace.
- Check return air: Ensure the return air grille is not blocked, which can cause abnormal pressure.
When to call a technician: Immediate professional inspection of the heat exchanger and combustion system is required.
Repair Difficulty
Required Part
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