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.
Related
- Status code 23 — Pressure switch did not open
- Status code 33 — Limit circuit fault — a limit or flame rollout switch is open
All codes for this manufacturer
Carrier, Bryant and Payne furnace status codes — every code, with what differs between models.
Do it yourself or call a technician?
The homeowner checks for this code are outdoors and at floor level, which is what makes them safe: the vent termination (snow, ice, leaves, nests — clear whatever you can see and reach from the ground) and the condensate trap and drain. Both are documented causes, neither requires opening the cabinet, and together they account for a real share of cold-snap appearances of this code. The third homeowner contribution is a weather log: Carrier lists excessive wind as a cause, and "it only happens on windy days" is a diagnosis-grade observation no technician can make in a single visit. Everything inside the cabinet — the switch, its tubing, the inducer, and any question of vent sizing — is professional work, and the pressure switch is never a component to bypass: it is the only thing standing between a blocked flue and a firing burner.
One cause only applies to some furnaces
Carrier's cause list ends with low inlet gas pressure, qualified "if LGPS used" — the low gas pressure switch is optional equipment, marked "when used" on the service manual's wiring schematic. On furnaces without one fitted, low gas pressure shows up as ignition-side codes instead of this one. Worth knowing before assuming the whole cause list applies to your unit.
The same fault on other brands
The stuck-open pressure switch is the most heavily documented fault in this site's index — the pressure switch codes hub tracks 47 codes across 12 control families, most of them this direction of failure. Direct equivalents: Goodman's 3 flashes, Lennox alert 223, Trane's E32, and Rheem's *RC controls' 2 blinks — did not close within 10 seconds. Carrier's version documents the retry rhythm the others mostly leave out: five minutes of trying, fifteen of waiting.
What the fix costs
Two parts dominate the paid outcomes in the repair cost guide: the pressure switch at $150–400 installed — the guide's note, check for a blocked flue first, is this code's whole story — and the inducer motor at $300–900, where brand parts availability drives the spread. The free outcomes are just as real: a cleared vent termination or condensate trap costs nothing, and a wind-exposed termination may need correcting rather than any part replacing. If the diagnosis is undersized venting, expect a quote for vent correction instead of a component — the durable fix for a furnace that only just proves draft and has faulted intermittently for years because of it. Inducer-side equivalents across brands: inducer motor codes.
What this looks like
From the outside, this usually shows up as the inducer spins up but the burners never fire — that walkthrough covers what to check in order, and when it stops being a homeowner job.