F8
Frigidaire
Low-Heat / High-Heat Stage Fault (Two-Stage Furnace)
Furnace flashes F8; blower may start but burners do not
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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 second-stage gas valve coil, Faulty staging thermostat signal, Loose W2 wiring, Control board staging fault
How to Fix / Troubleshooting
Safety: Turn off power and gas before servicing gas valve wiring.
- 1. Check thermostat staging: Ensure your thermostat is compatible with two-stage heating and wired correctly (W1/W2).
- 2. Inspect W2 wiring: At the furnace control board, verify the W2 terminal is wired correctly and the connection is tight.
- 3. Gas valve coil check: A technician should measure resistance of the second-stage coil and verify 24V is present when W2 is energized.
- 4. Board replacement: If the gas valve and wiring are good, the control board staging circuit may be defective and require replacement.
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Repair Difficulty
Hard
4/5
Required Part
Two-Stage Gas Valve
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