Carrier Furnace Error Code 31

Code 31 means the pressure switch did not close when the inducer motor started, or it opened back up during the heating cycle. This switch confirms that proper combustion airflow and draft are present before the furnace proceeds to ignition. If the switch stays open for more than 5 minutes, the inducer shuts off and the furnace waits 15 minutes before retrying. Common causes include a blocked vent, a faulty pressure switch, or a failing inducer motor.

Code 31 indicates the furnace's own safety controls have stopped the heating cycle because proper draft cannot be confirmed. Running the furnace without resolving the underlying cause could mean combustion gases are not being properly vented. The furnace will generally refuse to fire while the fault is active, but you should not attempt to bypass the pressure switch. Have the system inspected before resuming normal operation.

Repair costs depend heavily on the specific cause. Clearing a blocked vent or reconnecting a pressure tube is a low-cost service call in the range of roughly $75 to $150 for labor. Replacing a pressure switch typically costs between $75 and $200 including parts and labor. An inducer motor replacement is the most expensive possibility, generally ranging from $300 to $700 or more depending on the model and labor rates in your area.

Some causes of code 31 are accessible to a knowledgeable DIYer. You can inspect the exterior vent termination for visible blockages such as ice or debris, check that the pressure tubing connected to the switch is not disconnected or kinked, and verify that combustion air vents in the equipment room are clear. Electrical testing of the inducer motor voltage and pressure switch continuity requires a multimeter and comfort working near live components. Replacing the inducer motor or pressure switch is a moderately advanced repair, and if you are unsure, calling a licensed HVAC technician is the safer choice.

Cycling power to the furnace or pressing the reset button will clear the fault from memory and allow the inducer to attempt another cycle. However, if the underlying cause has not been corrected, the fault will return within the same heating cycle or shortly after. The 15-minute retry delay built into the control logic means the furnace may attempt a self-recovery on its own, but a persistent code 31 requires diagnosis and repair rather than repeated resets.