9 FLASH
Armstrong Air
Incorrect Line Voltage or Grounding / Polarity Error
Furnace does not respond to thermostat; LED flashes 9 times repeatedly on Armstrong Air control 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
Reversed hot and neutral at service panel, Open neutral, Floating ground, Miswired furnace disconnect
How to Fix / Troubleshooting
Safety: This is a line-voltage wiring issue. If you are not trained in electrical work, contact a licensed electrician.
Steps to check:
- Confirm breaker and wiring: Turn off the furnace breaker. Remove the furnace electrical access cover and verify that the incoming hot, neutral, and ground are correctly connected and secure.
- Test polarity: Using a plug-in outlet tester or multimeter at the furnace service outlet (if present), verify correct hot/neutral orientation and ground presence.
- Inspect junction boxes: Trace the furnace circuit back to the main panel, checking for any intermediate junction boxes where wires may have been misconnected.
- After correction: Restore power and observe the LED. If the 9-flash code persists, the control board may have been damaged and require replacement.
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Repair Difficulty
Hard
4/5
Required Part
Integrated Furnace Control Board
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