Bryant 355MAV Error Code 31: High-Heat Pressure Switch or Relay Did Not Close or Reopened
What Does Code 31 Mean?
Status code 31 on the Bryant 355MAV means the high-heat pressure switch input failed to close on a call for high-heat, or opened during high-heat operation. The pressure switch is a safety device that confirms the inducer is producing enough draft to vent combustion gases before and during firing.
On a call for high-heat the inducer runs at high speed, creating negative pressure the switch must sense. If the switch does not close, or reopens mid-cycle, the board shuts the furnace down rather than risk exhaust spilling into the home. Because the 355MAV is a two-stage furnace, this high-heat switch is separate from the low-heat switch tied to code 32 (Low-Heat Pressure Switch Did Not Close or Reopened), which monitors the lighter draft of low-heat firing.
The most common cause is a blocked or restricted exhaust vent or combustion-air intake — snow, ice, leaves, or nests at the outside terminations. A defective control relay or a mis-wired gas valve are less common causes the manual also lists. While a homeowner can safely look for an obviously blocked outdoor vent, confirming draft, testing the switch, and checking the relay or valve wiring is technician work on this model.
What You'll Notice
- The furnace starts the inducer but shuts down before or shortly after igniting on high-heat
- Heat may work on low-heat but fail whenever the furnace tries to step up to high-heat
- The status LED flashes code 31 (three short flashes, one long flash)
- The problem may worsen in snow, ice, or high wind that affects the vent termination
- Short-cycling or repeated no-heat calls during cold weather when high-heat is demanded
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Blocked or restricted vent/exhaust pipe | Most common | ✗ Call a pro → |
| Defective control relay | Uncommon | ✗ Call a pro → |
How This Is Diagnosed
A technician first checks the exhaust and intake terminations outside for blockage, then measures the actual draft pressure the inducer develops at high speed against the switch's rated set point. A weak inducer, a partially blocked vent, or water sagging in the piping can all leave the switch unable to close.
If draft is adequate but the switch still will not close, the switch and its tubing are tested, and finally the control relay and gas valve wiring are checked, since the manual lists a defective relay or mis-wired valve as possible causes. These draft and electrical checks require gauges and access to the inducer assembly, so they are done by a qualified technician.
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 outdoor vent and intake look clear but code 31 persists
- The inducer sounds weak, loud, or does not run up to speed
- Ice keeps reforming at the vent termination after being cleared
- The code appears mainly on windy days, hinting at an improper vent termination
- The switch, control relay, or gas valve wiring is suspected
Frequently Asked Questions
What can I safely check myself for code 31?
You can safely look outside for an obviously blocked exhaust or intake pipe — snow, ice, leaves, or a nest — and clear it. Verifying draft pressure, testing the pressure switch, and checking the relay or gas valve wiring should be left to a technician.
Why does my furnace only fail on high heat?
The 355MAV is two-stage and uses a separate high-heat pressure switch. High-heat needs more draft, so a partial vent restriction or weak inducer can fail the high-heat switch (code 31) even when low-heat still runs.
Sources
✓ Verified against manufacturer service manual — March 2026