Carrier furnace Status code 31: Pressure switch did not close, or reopened
Code 31 means the inducer ran and the pressure switch never closed, or closed and then reopened. If it stays open more than five minutes, the inducer shuts off for fifteen minutes before retrying.
Applies to: Carrier 58MCB four-way multipoise condensing gas furnaces and related models using the same integrated furnace control. Bryant and Payne furnaces of the same generation use the same control and code set.
What it means
This is the draft-proving failure, and on condensing furnaces it is the most common fault code there is. The control runs the inducer and waits for the pressure switch to close, confirming enough air is moving to carry combustion products safely out of the house. Carrier documents specific timing: if the switch is open longer than five minutes, the inducer shuts off for fifteen minutes before trying again. That produces a furnace that appears to attempt heating periodically and give up. Carrier also notes that if the switch opens during the blower on-delay period, the blower will run for the selected blower off-delay — normal behaviour worth recognising rather than treating as a second fault.
Most common causes
- A restricted vent, which Carrier lists explicitly.
- Improper vent sizing.
- Excessive wind at the termination, which Carrier documents as a cause.
- Inadequate combustion air supply.
- A defective inducer motor, or low inducer voltage.
- A defective pressure switch.
- Disconnected or obstructed pressure tubing.
- Low inlet gas pressure, where a low gas pressure switch is fitted.
How to diagnose it
- Look at the outside vent termination first. Snow, ice, leaves, and nests are the highest-yield check and need no tools.
- Listen for the inducer. If it runs and nothing follows, the switch is not seeing the draft.
- Note the timing pattern — a five-minute wait followed by a fifteen-minute pause matches Carrier's documented behaviour and confirms the code.
- Note the weather. Carrier lists excessive wind as a cause, and this fault clustering on windy or freezing days is meaningful.
- Check the condensate drain and trap for standing water.
How to fix it
- Clear the vent termination if blocked, and keep both pipes clear of snow, ice, and vegetation.
- Clear a blocked condensate drain — reasonable homeowner work on most installations.
- The pressure switch, tubing, inducer, and vent system inside the cabinet are technician work.
- If vent sizing is wrong for the furnace, have it corrected rather than worked around. A furnace that only just proves draft faults intermittently for years.
- Never bypass the pressure switch. A blocked flue with a firing burner is how carbon monoxide enters a house.
Notes
Carrier explicitly lists excessive wind among the causes, which is unusual and useful. A furnace that fails only in particular weather is not necessarily faulty — the termination may be exposed in a way the installation did not account for.