Error Code 43

Bryant 355MAV Error Code 43: Low-Heat Pressure Switch Open While High-Heat Pressure Switch Is Closed

TL;DR

Low-heat pressure switch is open while the high-heat pressure switch is closed. Most likely cause: plugged condensate drain.

Disclaimer

This article is for informational purposes only and does not guarantee the accuracy or completeness of the information provided. Always turn off power and gas supply before attempting any repairs. If you smell gas, leave immediately and call your gas company. Consult a licensed HVAC technician for diagnosis and repair. Any actions taken based on this information are at your own risk.

What Does Code 43 Mean?

Low-heat pressure switch is open while the high-heat pressure switch is closed.

Common Causes

Cause	Likelihood	DIY?
Plugged condensate drain	Most common	✓ DIY fix →
Low inlet gas pressure (if LGPS used)	Common	✗ Call a pro →
Stuck open low-heat pressure switch	Common	✗ Call a pro →
Disconnected or obstructed pressure tubing	Common	✗ Call a pro →
Water in vent piping (sagging pipe)	Uncommon	✓ DIY fix →
Improper pressure switch wiring	Rare	✗ Call a pro →

When to Call a Professional

Contact a licensed HVAC technician if:

Basic troubleshooting did not resolve the error
You smell gas at any point during the process
You are not comfortable working around gas lines or electrical components
The unit needs a gas valve, control board, or motor replacement

Sources

Bryant 355MAV Troubleshooting Manual, Component Test (Page 8)