Carrier 58MVC Error Code Status Code 31: Medium-Heat Pressure Switch or HPSR Relay Did Not Close or Reopened

What Does Code Status Code 31 Mean?

The pressure switch is a safety device that verifies the inducer motor is creating enough draft to safely vent combustion gases out of your home. On the 58MVC, code 31 specifically relates to the medium-heat pressure switch — it either failed to close when the inducer started (meaning insufficient draft was detected), or it opened during medium- or high-heat operation (meaning draft was lost mid-cycle).

The most common cause is a physical blockage somewhere in the venting system. This can be debris, ice, bird nests, or even a disconnected vent pipe. A plugged condensate drain is also a frequent culprit — when condensate water cannot drain properly, it backs up into the inducer housing or vent system and blocks airflow. Disconnected or cracked pressure tubing between the inducer and the pressure switch can also prevent the switch from sensing proper draft.

Less commonly, this code can indicate low inlet gas pressure (if a low gas pressure switch is installed), a defective inducer motor that is not generating sufficient draft, or a failed pressure switch itself. If you also see code 32 (low-heat pressure switch), the issue is likely in the shared venting or condensate system rather than a switch-specific problem.

Common Causes

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

What You'll Need

• Flashlight
• Wet/dry vacuum (optional, for condensate drain)

Steps

1. Turn off power at the breaker or power switch AND shut off the gas supply Locate the furnace circuit breaker and turn it OFF. Find the gas shutoff valve on the supply line to the furnace and turn it to the closed position (perpendicular to the pipe). If you smell gas, leave immediately and call your gas company.
2. Inspect the exhaust vent pipe for blockages Follow the PVC exhaust vent pipe from the furnace to where it exits the building. Look for any obvious blockages, disconnections, sagging sections, or damage. If the vent terminates outside, check the exterior opening for ice buildup, debris, bird nests, or insect nests. Clear any obstructions you can safely reach. Make sure vent pipes have proper slope (no sagging sections where water can pool).
3. Check the condensate drain for clogs Locate the condensate drain line — it is a small-diameter PVC pipe that exits the furnace (typically from the inducer or collector box area). Check that it is not plugged, kinked, or frozen. If the drain trap is accessible, check that it has water in it (a dry trap can allow exhaust gases to escape). If the line appears clogged, you can try clearing it with a wet/dry vacuum on the drain end.
4. Inspect the pressure tubing connections Look for small rubber or silicone tubes running from the inducer housing to the pressure switch(es) on the control board area. Make sure these tubes are firmly connected at both ends, are not cracked or split, and are not kinked or filled with water. If a tube has water in it, carefully disconnect it and drain the water, then reconnect.
5. Restore power and gas, then test Turn the gas supply valve back to the open position (parallel to the pipe). Turn the breaker back ON. Set your thermostat to call for heat and observe whether the furnace completes its startup sequence without triggering code 31 again.

When to Call a Professional

Contact a licensed HVAC technician if:

• Code 31 returns after clearing vent blockages and checking the condensate drain
• You cannot access or inspect the full length of the exhaust vent
• The inducer motor sounds abnormally loud, is vibrating, or does not start at all
• The pressure switch tubing appears intact but the switch still does not close
• You also see code 32 and the problem persists after basic checks
• The furnace is a high-efficiency (condensing) model and condensate is backing up repeatedly