Lennox Furnace Error Code 9 Flashes

9 Flashes on a Lennox furnace with Control 103085 indicates that the control board has detected incorrect line voltage polarity at the furnace power connection. This means the hot (line) and neutral wires are connected to the wrong terminals. The furnace will not operate until the polarity is corrected. This is an electrical wiring issue, not a mechanical or component failure in most cases.

Yes, reversed line voltage polarity is a legitimate electrical safety concern. When hot and neutral are swapped, components like switches and controls may remain energized even when they appear to be off, creating a shock hazard. The furnace control board flags this condition and refuses to operate specifically because of these risks. The wiring should be corrected before the furnace is returned to service.

If only the wires need to be switched at the furnace power connection, the repair is typically a low-cost service call, generally in the range of $75 to $150 for a technician's time. If the issue involves rewiring a disconnect, junction box, or panel correction, costs could rise to $150 to $400 or more depending on the scope of work. No parts are typically required unless the control board was damaged by prolonged operation with reversed polarity.

To fix this error, turn off power to the furnace at both the local disconnect and the circuit breaker. Then switch the line and neutral wires at the furnace's power connection terminals. Restore power and observe whether the fault clears. If it does not clear, verify polarity at the upstream disconnect or junction box using a multimeter to confirm the issue is not further back in the circuit.

No, resetting the furnace will not clear the 9 Flashes error if the underlying polarity problem has not been corrected. The control board continuously detects the reversed polarity condition at startup and will re-issue the fault code. The wiring must be corrected first, after which the board should clear the fault automatically when power is restored.