Furnace LED flashes code 42; inducer or blower may run unexpectedly, or furnace may short-cycle. Often indicates inducer or gas valve relay fault.
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: Turn off power before inspecting the control board.
- Power reset: Turn furnace power OFF for 5 minutes, then ON, and observe whether the inducer or blower still runs when there is no call for heat.
- Check for overheating: Smell for burnt electronics near the control board. Look for discoloration or burn marks on the board around the relays.
- Inspect inducer/blower wiring: Ensure there are no shorts or melted insulation on the motor leads.
If the inducer or gas valve is being energized without a call for heat, the control board relay is likely stuck. The integrated furnace control board should be replaced by a qualified technician.
Repair Difficulty
Required Part
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