Code 43 — Furnace LPS Open HPS Closed

What does 43 mean?

This fault indicates an unusual and potentially dangerous state where the Furnace's Low Pressure Switch (LPS) is open, but the High Pressure Switch (HPS) is closed. This suggests conflicting or incorrect pressure readings.

• Faulty pressure switches
• Wiring issue to the pressure switches
• Control board malfunction misinterpreting sensor data
• Severe refrigerant system imbalance (unlikely in furnaces unless integrated HP)

Click steps to track your progress.

1. 1

   Turn off the power to the furnace at the circuit breaker for 30 seconds to reset.

2. 2

   Verify that air filters are clean and air vents are open.

3. 3

   Ensure the outdoor unit (if applicable) is clear of debris.

4. 4

   Due to the conflicting pressure readings, contact a qualified HVAC technician immediately for diagnosis.