9 FLASH
Miller
Line Voltage Polarity or Ground Fault
Furnace will not run; Miller LED flashes 9 times in a repeating pattern.
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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
Reversed hot and neutral at furnace, Open equipment ground, Shared neutral issues, Faulty control board sensing circuit
How to Fix / Troubleshooting
Safety: This involves line-voltage wiring. If you are not comfortable working with 120V circuits, contact a licensed electrician or HVAC technician.
- Turn off breaker: Shut off the furnace circuit at the main panel.
- Inspect junction box wiring: Remove the cover on the furnace electrical junction box. Verify that the black (hot) wire is connected to the L (line) terminal, the white (neutral) to N, and the green or bare wire to ground.
- Check outlet (if cord-connected): Use a plug-in outlet tester to confirm correct polarity and ground at the receptacle serving the Miller furnace.
- Tighten ground connections: Ensure the ground wire is securely attached to the furnace chassis and that there is continuity between the chassis and the electrical panel ground.
- Board replacement: If wiring and supply are correct but the code persists, the control board's line-sensing circuit may be defective and require replacement.
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Repair Difficulty
Hard
4/5
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