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 flags a disagreement between the two staged pressure switches: the low-heat pressure switch is open at the same time the high-heat pressure switch is closed. That combination should not happen in normal operation, because the low-heat switch proves draft at the lower firing rate and would normally be closed whenever the high-heat switch is closed.
This code is closely tied to codes 31 and 32. Code 31 concerns the high-heat pressure-switch proof and code 32 the low-heat pressure-switch proof; code 43 is specifically the logical conflict between the two — the control seeing a high-heat proof without the corresponding low-heat proof. Bryant lists the causes as mis-wired pressure switches, a low-heat pressure switch stuck open, low inlet gas pressure (where a low gas pressure switch is used), and disconnected or obstructed pressure tubing.
Because every listed cause involves the pressure-switch wiring, the switches themselves, or the pressure tubing on this induced-combustion furnace, code 43 is diagnosed and corrected by a technician rather than the homeowner.
What You'll Notice
- The furnace fails to run a normal heating cycle and flags a pressure-switch conflict
- The status LED flashes four short then three long flashes
- The problem may appear right after pressure-switch or tubing service, if switches were swapped or tubes mis-routed
- Heating is unreliable because the control cannot confirm a consistent draft proof across stages
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 → |
How This Is Diagnosed
A technician checks the pressure-switch circuit against the wiring diagram to rule out mis-wired or swapped low-heat and high-heat switches, then tests whether the low-heat switch is stuck open. They inspect the pressure tubing to each switch for disconnection or obstruction and, where a low gas pressure switch is used, consider low inlet gas pressure. The goal is to explain why the high-heat proof is present without the low-heat proof.
When to Call a Professional
This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:
- The furnace will not run a normal cycle and reports a pressure-switch conflict
- The code appeared after pressure-switch or pressure-tubing service
- A low-heat pressure switch is suspected stuck open or a tube is disconnected
- Any pressure-switch wiring or tubing diagnosis, which is not a homeowner repair
Frequently Asked Questions
What does code 43 mean on my Bryant 315AAV?
It means the low-heat pressure switch is open while the high-heat pressure switch is closed — a contradictory state. Common causes are mis-wired switches, a stuck-open low-heat switch, or disconnected pressure tubing.
How is code 43 related to codes 31 and 32?
Did my recent repair cause this?
It can. Mis-wired or swapped pressure switches and mis-routed pressure tubing are listed causes and often trace to recent service, so a technician should verify the connections against the wiring diagram.
Sources
✓ Verified against manufacturer service manual — March 2026