HeatingCodes

Carrier furnace status codes

By Jason Dearmin · Last reviewed November 14, 2026

Carrier furnaces in this family report faults through a status-code LED that you can see through the sight glass in the blower door. The control also keeps recent codes in memory, which helps when a fault comes and goes.

What this table coversCodes from Carrier's SP05-59 service procedures for the Deluxe 4-way multipoise 2-stage direct-vent condensing gas furnace. Other boards can differ; the service label on the back of your main furnace door is the final authority.

How to read the display

Each status code is a two-digit number. The first digit is the number of short flashes and the second digit is the number of long flashes. So code 33 is three short flashes followed by three long flashes.

A steady LED means something different from a code. Continuous off means check for 115 VAC power at the control and 24 VAC at the transformer. Continuous on means the control has 24 VAC power. Rapid flashing means the 115 VAC line voltage polarity is reversed.

Stored codes are erased automatically after 72 hours. Code 11 appears when there is no previous code to show.

Carrier code table

CodeMeaningWhat the document says
11 No previous code Stored status codes are erased automatically after 72 hours. On red-LED boards they can also be erased when 115 VAC or 24 VAC power to the control is interrupted.
12 Blower on after power up (115 VAC or 24 VAC) Blower runs for the selected blower-off delay if the unit is powered up during a call for heat, or if the thermostat call for heat opens during the blower on-delay.
13 Limit circuit lockout Lockout occurs if a limit or flame rollout switch is open longer than 3 minutes. The control resets automatically after three hours. See code 33. Full explanation
14 Ignition lockout The control resets automatically after three hours. See code 34. Full explanation
21 Gas heating lockout The control will not reset automatically. Check for a mis-wired gas valve or a defective control (valve relay).
22 Abnormal flame-proving signal Flame is proved while the gas valve is de-energized. The inducer runs until the fault is cleared. Check for a leaky or stuck-open gas valve.
23 Pressure switch did not open Check for obstructed pressure tubing or a pressure switch stuck closed.
24 Secondary voltage fuse is open Check for a short circuit in the 24 VAC wiring.
31 High-heat pressure switch or relay did not close or reopened The control relay may be defective; see code 32.
32 Low-heat pressure switch did not close or reopened If open longer than five minutes, the inducer shuts off for 15 minutes before a retry. Check for excessive wind, a restricted vent, a defective inducer motor, low inlet gas pressure (if a low gas pressure switch is used), a defective pressure switch, low inducer voltage, inadequate combustion air, vent sizing, and disconnected or obstructed pressure tubing. Full explanation
33 Limit circuit fault A limit or flame rollout switch is open. The blower runs for 4 minutes or until the open switch closes, whichever is longer. If it stays open longer than 3 minutes the code changes to lockout 13. A flame rollout switch requires a manual reset. Full explanation
34 Ignition proving failure The control tries three more times before ignition lockout 14 occurs. See the full check list on the code 34 page. Full explanation
43 Low-heat pressure switch open while high-heat pressure switch is closed Check for disconnected or obstructed pressure tubing, mis-wired pressure switches, a low-heat pressure switch stuck open, and low inlet gas pressure (if a low gas pressure switch is used).
45 Control circuitry lockout Auto-resets after a one-hour lockout caused by a gas valve relay stuck open, a flame-sense circuit failure or a software check error. Reset power to clear the lockout. Replace the control if the code repeats.

Source: Carrier SP05-59, status code table. Only codes printed in that document are listed.

Detailed explanations

SafetyThese tables describe what the manufacturer documents say. Gas, combustion, refrigerant and line-voltage repairs are for licensed professionals. If you smell gas, leave the building and call your gas utility or 911. Safety disclaimer.

Sources