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ErrBase

Carrier Furnace Error Codes

All Carrier furnace error codes with step-by-step troubleshooting, multimeter specs, and OEM part numbers.

8 error codes

CodeMeaning
12Code 12 on a Carrier furnace means the blower motor failed to reach operating speed within the expected time after a heat call, or the motor stopped unexpectedly during a run cycle. The control board monitors blower motor performance and triggers this fault when the motor does not respond correctly.
moderateintermediate
13Code 13 on a Carrier furnace means the high limit switch or a secondary safety limit (rollout switch) has tripped. These switches are thermal cutoffs that open when the furnace detects dangerously high temperatures inside the heat exchanger or combustion chamber. The furnace shuts down completely to prevent damage or fire.
highintermediate
14Code 14 on a Carrier furnace is an extended ignition lockout triggered by repeated failed ignition attempts. The control board has tried to light the furnace multiple times (typically 3 cycles), each time resulting in Code 34 (ignition proving failure), and has now locked out entirely. The furnace will not attempt another ignition cycle until it is manually reset.
highintermediate
3 Short 3 LongCode 33 on a Carrier furnace means the pressure switch circuit is open. The pressure switch is a safety device that verifies the inducer motor has created enough negative pressure (draft) before allowing the gas valve to open. When the switch stays open during a heating cycle, the furnace shuts down to prevent unburned gas from accumulating.
highintermediate
31Code 31 on a Carrier furnace indicates the gas valve is not opening or is closing prematurely during a heating cycle. The control board sends a 24VAC signal to the gas valve solenoid at the appropriate time in the sequence, but the valve either fails to open or opens and then closes before the ignitor and flame sensor complete their cycle.
highadvanced
34Code 34 on a Carrier furnace means the furnace attempted ignition but the flame sensor did not detect a stable flame within the proving period. The control board gives the gas valve and ignitor one attempt (on most models), then shuts down if no flame signal is received within roughly 7-10 seconds of gas valve opening.
highintermediate
HUBThis hub covers all Carrier furnace LED flash fault codes. Carrier furnaces use a single LED on the control board that blinks in short and long patterns to communicate fault codes. Counting the blink sequence identifies the specific fault.
lowbeginner
RESETResetting a Carrier furnace clears the stored fault code from the control board and allows the furnace to attempt a new startup sequence. There are two levels of reset: a soft reset via the thermostat and a hard reset via the circuit breaker. A third manual reset is required for Code 13 rollout lockouts and is specific to the physical rollout switch inside the cabinet.
lowbeginner