STEADY RED ON
Coleman
Control Board Internal Fault
Status LED is on solid red with no flashing; furnace does not respond to thermostat commands.
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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
Failed integrated furnace control board, Power surge or lightning damage, Shorted low-voltage wiring, Incorrect replacement board installed
How to Fix / Troubleshooting
Safety first: Turn off power to the furnace before touching any wiring or boards.
Steps to check:
- Verify power supply: Confirm 120 VAC is present at the furnace line terminals and 24 VAC is present between R and C on the control board. If either is missing, correct the upstream power issue.
- Inspect low-voltage wiring: Look for shorts between thermostat wires (R, W, Y, G) or wires pinched under the furnace cabinet. Repair any damaged insulation and secure wires away from sharp edges.
- Reset furnace: Turn off power for at least 30 seconds, then restore. If the LED returns to steady red with no operation, the board is likely failed.
- Board replacement: Replace the integrated furnace control with the exact Coleman OEM board or approved replacement. Transfer each wire one at a time from the old board to the new to avoid miswiring.
Because miswiring can damage the new board, board replacement is best handled by a qualified technician.
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Repair Difficulty
Hard
4/5
Required Part
Integrated Furnace Control Board
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