Code 31: Pressure / draft safeguard / aux-limit switch did not close, or reopened
Homeowner checks
The big venting code on this family. Manual list: vent sizing, restricted vent, weak or dead inducer motor, bad pressure switch, excessive wind, disconnected or blocked pressure tubing, inadequate combustion air. If it opens after ignition, you get a 90-second recycle delay; open past five minutes and the inducer rests 15 minutes.
From the table: Two-digit status codes — short flashes, then long flashes — source: Carrier 58YAV Service section - status code table (read the document, fetched 2026-10-30). Covers: Carrier 58-series and their Bryant/Payne twins. First digit = number of short flashes; second digit = number of long flashes. Code 33 is 3 short, pause, 3 long.
Read the manual's list slowly, because it is ordered like a diagnosis: proper vent sizing; restricted vent; defective inducer motor; defective pressure switch; excessive wind; disconnected or obstructed pressure tubing; inadequate combustion air supply. Two behaviors modify the story: if the switch opens after ignition, you get a 90-second recycle delay instead of a hard stop; and if it stays open past five minutes, the inducer shuts off for fifteen minutes before the next retry — a furnace that seems to give up and then mysteriously tries again later is often just living inside this code.
The homeowner end of the list is the outdoor vent terminal and, on condensing furnaces, the condensate drain — a slow drain backs water into exactly the wrong places and trips this same switch.
Homeowner checks — the safe list:
- Go outside and look at the vent and intake pipes. Snow, ice, leaves, a nest, or a mulch pile against the terminal can cause exactly this code.
- On a condensing (90%+) furnace, check the condensate drain: a backed-up drain or frozen drain line trips the same switch.
- Air filter: a starved furnace is a furnace that overheats and behaves badly in several code families.
- Make sure the blower door is fully seated after you look at the light.
31 versus 32
Carrier's 48XL manual carries a near-twin, code 32 — "pressure switch or relay did not close or reopened." Different Carrier documents split this fault across the two numbers with slightly different wording. If your board shows 32, the diagnosis path is the same venting list; your model's manual decides which number your board prints.
The two rules that outrank everything on this page.
1. Smell gas? Stop reading. Leave the house and call your gas utility or 911 from outside. No code is worth diagnosing through a gas smell.
2. Never bypass a safety switch — no jumping a pressure switch, no taping a limit, no propping a rollout. Those switches are the only thing between a furnace fault and a fire or carbon-monoxide problem. This library explains codes; it does not teach repairs inside the cabinet.
One honesty note before the tables: codes change between control boards, sometimes inside the same brand and the same decade. Every table below names the board and the manual it was transcribed from. The chart glued inside your own blower door is the final word for your furnace — if it disagrees with this page, believe the door.