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Home > Error Codes > Carrier
Every documented Carrier furnace error code with causes, fixes, and the parts you may need. Also covers: Bryant, Payne.
Code 11 (1 short + 1 long)
No Previous Code
No fault has been recorded. The system memory is clear. This is normal after a power cycle.
DIY check: No action needed. This is an informational status, not a fault.
Code 12 (1 short + 2 long)
Blower On After Power Up
The blower motor runs immediately when power is applied, before any call for heat. Usually means the thermostat was calling for heat during a power interruption.
DIY check: Check thermostat settings. If the blower runs continuously with no heat, check the fan switch setting (AUTO vs ON).
Code 13 (1 short + 3 long)
Limit Circuit Lockout
The high limit or flame rollout switch has been open for more than 3 minutes continuously. The furnace locks out for safety. Auto-resets after 3 hours, or manually reset by cycling power.
DIY check: Check for a dirty air filter (most common cause), closed or blocked supply registers, undersized ductwork, or a failed blower motor. If the rollout switch tripped, do NOT reset it without a technician inspecting the heat exchanger.
Common part needed: Shop Flame Sensor →
Code 14 (1 short + 4 long)
Ignition Lockout
The furnace failed to ignite after the maximum number of retry attempts. Hard lockout requiring manual reset (power cycle). The igniter glowed but gas did not light, or the igniter itself failed.
DIY check: Check: is the gas supply on? Is the gas valve open? Try cleaning the igniter with fine-grit emery cloth. Check for cracked igniter (visible fracture = replace). Verify gas pressure if you have a manometer.
Common part needed: Shop Igniter →
Code 21 (2 short + 1 long)
Gas Heating Lockout
Gas valve energized but the control did not detect flame, or invalid model/personality plug configuration. On some boards this indicates the personality connector (PL5) is missing or jumpered incorrectly.
DIY check: Check: gas valve wiring for shorts or damage. Verify the personality plug PL5 is seated correctly. If you recently replaced the control board, ensure the correct plug was transferred.
Common part needed: Shop Control Board →
Code 22 (2 short + 2 long)
Abnormal Flame Signal / Setup Error
Flame was detected when the gas valve was supposed to be closed (could indicate a leaking gas valve), OR a setup/DIP switch error on the control board.
DIY check: If flame-related: this is a potential gas leak situation. Turn off gas and call a technician immediately. If setup-related: check DIP switches SW-1 and SW-6 are in the correct position per the installation manual.
Common part needed: Shop Gas Valve →
Code 23 (2 short + 3 long)
Pressure Switch Did Not Open
The pressure switch did not open when expected, or stayed closed when the inducer was not running. The inducer may run continuously.
DIY check: Check: is the pressure switch hose cracked or disconnected? Is the switch stuck closed? Tap it gently. Some techs replace the switch if it sticks repeatedly. Check for water in the hose.
Common part needed: Shop Pressure Switch →
Code 24 (2 short + 4 long)
Secondary Voltage Fuse Open
The 3-amp or 5-amp fuse on the control board has blown. No 24V power to thermostat or gas valve. Thermostat screen may be blank.
DIY check: Check for: short circuit in thermostat wiring (common if a wire touches the chassis), shorted gas valve coil, or shorted humidifier/accessories wired to the board. Replace the fuse only after finding and fixing the short.
Common part needed: Shop Transformer →
Code 26 (2 short + 6 long)
Flame Rollout Switch Open
The flame rollout safety switch has tripped. This switch is mounted near the burners and detects flame escaping the combustion chamber. Requires manual reset (red button on the switch).
DIY check: DO NOT simply reset the switch and run the furnace. Flame rollout can indicate a cracked heat exchanger, blocked flue, or backdrafting. Call a technician to inspect the heat exchanger before operating the furnace.
Code 31 (3 short + 1 long)
Pressure / Draft Safeguard Switch Fault
The pressure switch did not close or reopened during operation. The inducer runs but the burners will not light. This is the most common Carrier error code.
DIY check: Check: blocked exhaust vent (bird nests, ice, debris), clogged condensate drain/trap (very common on 90%+ furnaces), cracked or disconnected pressure hose, weak inducer motor. Clear the condensate trap first - it fixes this code about 40% of the time.
Common part needed: Shop Pressure Switch →
Code 32 (3 short + 2 long)
Low Pressure Switch Fault
On two-stage furnaces, the low-fire pressure switch did not close or reopened. Similar causes to Code 31 but specific to the low-heat stage.
DIY check: Same checks as Code 31: condensate drain, vent blockage, pressure hose, inducer motor. Also check that the correct pressure switch is installed for the furnace model (different switches for different vent lengths).
Common part needed: Shop Pressure Switch →
Code 33 (3 short + 3 long)
Limit Switch or Flame Rollout Switch Open
The high-temperature limit switch tripped due to overheating, or a flame rollout switch opened. The blower may run continuously trying to cool the heat exchanger. If open more than 3 minutes, escalates to Code 13 lockout.
DIY check: Check air filter FIRST (dirty filter is the #1 cause). Then: are all supply registers open? Is the blower wheel clogged with dust? Is the blower motor running at the correct speed? Is the A-coil above the furnace clean or iced up?
Common part needed: Shop Fan Motor →
Code 34 (3 short + 4 long)
Ignition Proving Failure / Flame Sensor
The burners ignited but the flame sensor could not detect or maintain a stable flame signal within the proving period (usually 7-10 seconds). This is the second most common Carrier error code.
DIY check: Clean the flame sensor with fine-grit emery cloth or steel wool (do NOT use sandpaper). The sensor is a thin metal rod near the burners. Remove it (one screw), clean the tip, reinstall. This fix works about 90% of the time.
Common part needed: Shop Flame Sensor →
Code 41 (4 short + 1 long)
Blower Motor Fault
The blower motor is not running, running at the wrong speed, or drawing excessive current. The control board detected an open motor circuit or the motor did not reach the target RPM.
DIY check: Check: is the blower motor humming but not spinning (bad capacitor)? Is the blower wheel jammed with debris? Is there 120V at the motor connector? On ECM/variable-speed motors, check for fault codes on the motor module itself.
Common part needed: Shop Fan Motor →
Code 42 (4 short + 2 long)
Inducer Motor Fault
The inducer (draft) motor is not running or not reaching the expected speed. On some boards, this indicates a wiring fault between the board and the inducer motor.
DIY check: Check: is the inducer motor humming but not spinning? Check capacitor if equipped. Verify 120V at the inducer connector. Listen for bearing noise (grinding = failing motor). Check for debris blocking the inducer wheel.
Common part needed: Shop Fan Motor →
Code 43 (4 short + 3 long)
Pressure Switch Calibration Fault
The low-pressure and high-pressure switch make points during the high-heat purge cycle are not within the expected calibration range. A diagnostic code, usually indicates incorrect switch installation or vent sizing.
DIY check: Verify the correct pressure switches are installed for the model and vent run length. Check for partial vent blockages that alter the pressure readings. This code may require a technician with a manometer.
Common part needed: Shop Pressure Switch →
Code 44 (4 short + 4 long)
Blower Calibration Fault
The calculated blower motor speed is below 250 RPM or above 1300 RPM. The system cannot achieve the target airflow at the configured settings.
DIY check: Check for undersized ductwork, excessively dirty filter, closed dampers, or a dirty/iced evaporator coil. On ECM motors, the motor may need replacement if it cannot maintain speed. Also check the blower wheel for buildup.
Common part needed: Shop Fan Motor →
Code 45 (4 short + 5 long)
Control Circuitry Lockout
Internal control board failure detected. The board's self-diagnostic has identified a fault in its own circuitry. Requires board replacement.
DIY check: Power cycle the furnace. If Code 45 returns immediately, the control board needs replacement. Note the board model number (printed on the board) before ordering.
Common part needed: Shop Control Board →
If the same code keeps coming back after you have addressed the obvious cause (dirty filter, flame sensor, etc.), or if you smell gas, see burn marks, or the furnace will not come out of lockout after a power cycle, call a licensed HVAC technician. Electrical and gas work carries real safety risk.