Furnace LED flashes code 42. The inducer or blower may run unexpectedly, or the furnace may short-cycle. This often indicates an 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 the furnace power OFF for 5 minutes, then turn it ON, and observe if the inducer or blower still runs when there is no call for heat.
- Check for overheating: Check for the smell of 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 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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