Lennox E111 Error Code

What does Lennox E111 mean?

E111 indicates that the line voltage power and neutral wires to the furnace are reversed. The Lennox communicating control board detects polarity and flags a reversed-polarity condition as a Service Soon/Urgent alert. The system shuts down and will not operate safely with reversed polarity. The alert clears five seconds after polarity is corrected and power is restored.

Symptoms

• E111 or 'Line Polarity Reversed' displayed on the thermostat.
• Furnace fails to start; system is shut down by the control.
• Alert appears immediately after initial installation or after wiring work on the circuit.
• No other mechanical symptoms — this is a pure wiring fault.

Common causes

• Line and neutral wires swapped at the equipment terminal block during installation.
• Reversed polarity at the electrical outlet or disconnect serving the equipment.
• Wiring error at the circuit breaker panel — line and neutral reversed on the branch circuit.
• Wiring error at a junction box upstream of the equipment.

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Diagnostic steps

1. Turn off power to the furnace at the circuit breaker

   De-energize the branch circuit fully before inspecting any wiring. Verify with a non-contact voltage tester at the equipment before proceeding.

2. Check polarity at the equipment terminal block

   Identify the line (hot) and neutral conductors at the furnace terminal strip. The hot conductor should connect to the Line terminal, the neutral to the Neutral terminal. On most systems, black = line, white = neutral.

3. Trace and correct reversed wiring

   If wires are confirmed reversed at the terminal block, swap them to the correct terminals. If they appear correct at the equipment, check the outlet, disconnect, and junction boxes upstream for the reversal.

4. Restore power and confirm E111 clears

   After correcting polarity, restore power. The control resumes normal operation five seconds after detecting correct polarity. Confirm E111 is no longer present and the furnace completes a normal startup.

When to call a professional

If the polarity reversal cannot be traced to the equipment wiring and appears to originate in the wall wiring or panel, a licensed electrician must correct the branch circuit. Reversed-polarity wiring is a National Electrical Code violation and a shock hazard on any equipment connected to the circuit.