Bryant 355MAV Error Code 31: High-Heat Pressure Switch Did Not Close or Reopened

What Does Code 31 Mean?

Status code 31 on the Bryant 355MAV means the high-heat pressure switch failed to close when the furnace called for high-heat, or it opened during a high-heat cycle. The pressure switch is a safety device that verifies the inducer motor is pulling enough draft through the heat exchanger and venting combustion gases properly before allowing the gas valve to open.

When the inducer motor runs, it creates negative pressure in the heat exchanger and vent system. The pressure switch senses this draft and closes its contacts, signaling to the control board that it is safe to proceed with ignition. If something is restricting the airflow — a blocked vent, a plugged condensate drain, or obstructed pressure tubing — the inducer cannot generate enough draft to close the switch.

Seasonal blockages are common. In winter, ice or snow can obstruct the exhaust vent termination outside your home. Bird nests, leaves, or insect nests can also block the vent pipe. A plugged condensate drain is another frequent culprit on condensing furnaces like the 355MAV — if condensate cannot drain freely, it backs up into the inducer housing and restricts airflow.

Common Causes

How to Fix It: Check Exhaust Vent, Condensate Drain, and Pressure Tubing

What You'll Need

• Flashlight
• Mirror (optional, for checking vent pipe interior)

Steps

1. Turn off power at the breaker or power switch and shut off the gas supply valve Locate your electrical panel and turn the furnace breaker to OFF. Find the gas shutoff valve on the gas line leading to the furnace and turn it to the closed (perpendicular to the pipe) position. If you smell gas, leave immediately and call your gas company.
2. Inspect the exhaust vent termination outside Go outside and locate where the furnace exhaust vent exits your home (usually a PVC pipe through the wall or roof). Check for any visible blockage: snow, ice, bird nests, leaves, insect nests, or debris. Clear any obstructions. Make sure the vent screen (if installed) is not clogged. In winter, ice buildup around the vent termination is a common cause.
3. Check the condensate drain The 355MAV is a condensing furnace that produces condensate (water) during operation. Locate the condensate drain line — it typically runs from the inducer housing or a collector box to a floor drain or condensate pump. Check that the drain line is not kinked, clogged, or frozen. If water is pooled in the inducer area, the drain is likely blocked.
4. Visually check the pressure tubing Look at the small rubber or vinyl tubes running from the pressure switch to the inducer housing. Make sure they are connected at both ends, not kinked, cracked, or visibly obstructed. If a tube has disconnected, push it firmly back onto the barb fitting. Do not blow into the tubes — if you suspect an internal blockage, a technician should handle it.
5. Restore power and gas Turn the gas supply valve back to open (parallel to the pipe). Turn the breaker back ON. Set the thermostat to call for heat and observe whether the furnace proceeds past the inducer stage.

When to Call a Professional

Contact a licensed HVAC technician if:

• The exhaust vent and condensate drain appear clear but code 31 persists
• The inducer motor sounds unusually loud, weak, or does not start at all
• You find water consistently pooling in the inducer housing despite clearing the drain
• Code 31 appears during windy weather (may need a vent termination wind guard)
• The pressure tubing connections appear intact but the switch still does not close
• Code 31 alternates with code 32 (low-heat pressure switch issue)