Bryant 315AAV Error Code 43: Low-Heat Pressure Switch Open While High-Heat Pressure Switch Is Closed
What Does Code 43 Mean?
Status code 43 on the Bryant 315AAV indicates an inconsistent pressure switch state: the low-heat pressure switch is open (not making contact) while the high-heat pressure switch is closed (making contact). On a two-stage furnace, both switches should be closed simultaneously during high-heat operation. When the low-heat switch is open while high-heat is active, the control detects a contradiction in the pressure sensing circuit.
The service documentation identifies three causes: miswired pressure switches, a low-heat pressure switch stuck in the open position, and disconnected or obstructed pressure tubing on the low-heat switch circuit. Miswired switches are a common post-service issue where the high-heat and low-heat switch connectors have been swapped. A stuck-open low-heat switch means the switch diaphragm cannot close even when the inducer is running. A disconnected or blocked tube prevents pressure from reaching the low-heat switch.
A technician will verify that the high-heat and low-heat switch connectors are installed on the correct switches (they may look identical but have different calibrated trip pressures), inspect the low-heat switch tubing, and test the switch contacts with a multimeter.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Mis-wired pressure switches | Common | ✗ Call a pro → |
| Low-heat pressure switch stuck open | Common | ✗ Call a pro → |
| Disconnected or obstructed pressure tubing | Common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- Contact a technician to inspect the low-heat pressure switch wiring, tubing, and switch function
- Verify that the high-heat and low-heat pressure switch connectors are not swapped — a common error after board or switch replacement
✓ Verified against manufacturer service manual — March 2026