Carrier error codes, explained
Carrier gas furnaces and light-commercial units (Bryant/Payne share the platform). Codes below: LED status codes (31, 33, 34, 13…). Each guide covers what the code means, what you can safely try yourself, when to stop and call a technician, and what the repair typically costs.
Carrier furnace Code 31 — Pressure switch did not close (or reopened)
The draft pressure switch never proved airflow through the vent system, so the furnace refuses to ignite. Per Carrier's service documentation, if it stays open more than 5 minutes the inducer shuts off for 15 minutes before retrying. Usual suspects: a blocked or restricted vent (check the outside termination for snow, ice, leaves, or nests), a weak draft inducer motor, disconnected pressure tubing, or — on high-efficiency condensing furnaces — a clogged condensate trap holding the switch open.
Carrier furnace Code 33 — Limit or flame rollout switch open
A safety circuit opened: either the high-temperature limit (the furnace overheated — almost always an airflow problem like a clogged filter, closed registers, or a dirty coil) or the flame rollout switch (flames escaped the burner box — a genuine combustion safety event). The distinction matters: limit trips are usually a filter change; a tripped rollout switch has a manual reset button and warrants professional inspection before you reset anything.
Carrier furnace Code 34 — Ignition proving failure
The burners tried to light but the control board never sensed flame. The overwhelmingly common cause is a dirty flame sensor (a $0 fix); others include the gas valve being off, low gas pressure, or a failing igniter. Three consecutive 34 failures escalate to Code 14 (ignition lockout), which auto-clears after 3 hours or with a 60-second power-off.
Carrier furnace Code 13 — Limit circuit lockout
The escalation of Code 33: the limit or rollout circuit stayed open more than 3 minutes, so the board locked out. It auto-resets after 3 hours. Same cause family as 33 — overheating from restricted airflow, or a tripped rollout switch.
How to read Carrier furnace LED codes
Carrier status codes are two-digit numbers blinked through the sight glass in the blower door: SHORT flashes are the tens digit, LONG flashes are the ones digit — so short-short-short then long = Code 31. Interrupting power for ~30 seconds clears the code; it comes right back if the fault is still present. Same scheme on Bryant and Payne (same manufacturer platform).