9 FLASHES
Concord Line Voltage Polarity or Ground Fault

Furnace will not operate; status LED shows 9 flashes repeating.

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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/neutral at furnace, Open equipment ground, Shared neutral issues, Faulty control board sensing circuit

How to Fix / Troubleshooting

Safety: This is an electrical wiring issue. If you are not experienced with 120 VAC wiring, contact a licensed electrician or HVAC technician.

Steps:

  • Check power source: Turn off the breaker. Remove the furnace electrical access cover. Verify that the hot (usually black) wire is connected to the L1 or HOT terminal and the neutral (white) wire to the NEUTRAL terminal on the Concord furnace.
  • Verify ground: Confirm that the green or bare copper ground wire is securely attached to the furnace chassis ground screw.
  • Inspect junction box: If the furnace is fed from a nearby junction box, open it and verify correct wire splicing and secure wirenuts.
  • Test with a meter: With power restored, use a multimeter to confirm 120 VAC between hot and neutral, and between hot and ground, and near 0 VAC between neutral and ground.

Note: If wiring is correct and the fault persists, the integrated furnace control may be misreading polarity and require replacement.

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Repair Difficulty

Hard 4/5

Required Part

Integrated Furnace Control Board
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