What This Error Means

The integrated furnace control detects that the incoming line and neutral polarity is reversed. The control is polarity sensitive and proper wiring is required for safe ignition and flame sensing.

Symptoms You May Notice

Furnace may not ignite; intermittent ignition or flame-sensing problems; electrical fault appears after installation, service or power wiring changes.

Common Causes

Hot and neutral conductors reversed; incorrectly wired service switch or receptacle; neutral wiring problem; generator or inverter connection issue; incorrect field wiring.

Safe Troubleshooting Steps

1. Turn off furnace power. 2. Do not move conductors unless qualified to perform line-voltage electrical work. 3. Inspect recent wiring changes. 4. A qualified technician or electrician should verify line, neutral and ground at the furnace, service switch and upstream circuit. 5. Correct polarity and confirm proper grounding before operating the furnace.

Parts Commonly Involved

Line-voltage supply; service switch; junction box; neutral conductor; integrated furnace control; grounding system.

When to Call a Technician

Yes. An HVAC technician or licensed electrician should correct the supply wiring.

Safety Notice

Line-voltage wiring can cause shock, fire or equipment damage. Disconnect power and use a qualified professional.

Manufacturer Documentation