Lennox Furnace Error Code E111

E111 means the furnace has detected that its line voltage polarity is reversed, indicating the hot and neutral wires supplying 120V power to the unit are swapped. This is a wiring fault, not a component failure. The furnace control board monitors incoming polarity and triggers this code when the conductors are in the wrong positions. The system will resume normal operation about 5 seconds after the correct wiring is restored.

Yes, reversed polarity is a genuine safety concern. With the hot and neutral wires swapped, certain components inside the furnace can remain energized when they should be isolated, which creates a potential shock hazard for anyone servicing the unit. It is important to correct the wiring before operating the furnace and to have the repair performed by a qualified technician or electrician.

Since E111 is a wiring issue rather than a parts failure, repair costs are typically limited to labor. If the fix is simply reversing two wires at the furnace terminal block, an HVAC technician visit could range from around $75 to $150 depending on your area. If the problem is at the breaker panel and requires a licensed electrician, costs could range from $100 to $250 or more depending on the complexity of the work.

Fixing E111 requires identifying where in the electrical circuit the hot and neutral wires are reversed and correcting that wiring. Start by turning off power at the breaker, then inspect the wiring at the furnace terminal block, any disconnect switch, and junction boxes in the circuit. Once the polarity is corrected and power is restored, the furnace should recover on its own within 5 seconds without needing a manual reset.

No, simply resetting the furnace will not clear E111 because the control board will continue to detect the reversed polarity every time power is applied. The fault clears automatically once the actual wiring is corrected. After fixing the polarity, the system resumes normal operation approximately 5 seconds after the fault condition is resolved.