Lennox Furnace Error Code 1

Error Code 1 on a Lennox furnace means the control board has detected a reverse line voltage polarity condition. This indicates that the hot and neutral wires supplying 120V AC power to the furnace are connected in the wrong positions. The furnace will not operate normally until the polarity is corrected. This is a wiring issue, not a component failure.

Yes, reversed polarity is a genuine electrical safety concern. When the hot and neutral wires are swapped, components inside the furnace that are supposed to be de-energized when a switch is open may remain energized, creating a shock or fire risk. The furnace control board is designed to detect and flag this condition to prevent unsafe operation. The wiring should be corrected by a qualified technician before the furnace is used.

The cost to fix a reversed polarity condition is typically low because no parts are required, only a wiring correction. Depending on your location and the technician or electrician you hire, labor for diagnosing and correcting the wiring typically falls in the range of $75 to $200. If the reversed polarity caused damage to any control board components, additional repair costs could apply.

Fixing this error requires identifying where the hot and neutral wires have been swapped in the furnace wiring circuit. Use a multimeter to check polarity at the furnace disconnect and wiring connections, confirming the hot conductor reads approximately 120V AC to ground. Always shut off the circuit breaker before touching any wiring. Because this involves line voltage electrical work, it is strongly recommended that a licensed electrician or HVAC technician perform the correction.

No, resetting the furnace will not clear Error Code 1. The control board checks for proper polarity as part of its startup routine, and the fault will return immediately if the underlying wiring issue has not been corrected. The error will only clear once the hot and neutral conductors are properly connected and the furnace detects correct polarity on the incoming power supply.