9 FLASHES
York
Line Voltage Polarity / Ground Fault
Furnace will not start; LED shows 9 flashes on York board.
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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
Hot and neutral reversed at furnace, Missing equipment ground, Shared neutral or bootleg ground, Faulty control board sensing circuit
How to Fix / Troubleshooting
Safety: This involves line voltage. If you are not comfortable working with 120V wiring, contact a licensed electrician or HVAC technician.
- Check receptacle or switch: If the furnace is plugged into a receptacle, use a plug-in outlet tester to verify correct hot/neutral/ground. If hard-wired, turn off breaker and visually inspect wiring connections in the furnace junction box.
- Verify ground: Ensure the green or bare ground wire is securely attached to the furnace chassis and that the metal cabinet is bonded.
- Panel and breaker: At the electrical panel, confirm the neutral is on the neutral bar and the hot is on the breaker. Do not move wires unless you are qualified.
- Reset furnace: After correcting any wiring issues, restore power and check if the 9-flash code clears.
- Professional help: If wiring is correct and the code persists, the control board's polarity detection circuit may be defective and require replacement.
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Repair Difficulty
Professional Required
5/5
Required Part
Integrated Furnace Control Board
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