What This Error Means

Carrier Error Code 31 indicates that the furnace control board did not receive the proper signal from the pressure switch during the heating cycle. The pressure switch confirms that the inducer motor is creating the correct draft for safe combustion before the burners are allowed to operate. In many cases, this fault is caused by a blocked vent pipe, clogged condensate drain, damaged pressure switch tubing, or an inducer motor that is not producing adequate draft. Less commonly, the pressure switch itself or the control board may be at fault. The furnace prevents ignition or shuts down the heating cycle because it cannot verify safe venting conditions. The underlying cause should be corrected before the furnace is returned to normal operation.

Symptoms You May Notice

• The furnace does not produce heat.
• The status LED flashes Error Code 31.
• The inducer motor may run without ignition.
• The furnace may attempt to start several times before shutting down.
• The heating cycle stops before the burners ignite.

Common Causes

• Blocked intake or exhaust vent
• Clogged condensate drain or trap
• Kinked or disconnected pressure switch tubing
• Faulty pressure switch
• Inducer motor not producing adequate draft
• Blocked condensate collector box
• Control board issue

Safe Troubleshooting Steps

1. Turn off power to the furnace before performing any inspection.

2. Inspect the intake and exhaust vent pipes for visible obstructions such as leaves, nests, snow, or debris.

3. Check the condensate drain and trap for obvious blockages or standing water.

4. Inspect the pressure switch tubing for cracks, kinks, or loose connections.

5. Restore power and restart the furnace.

6. If Error Code 31 returns, discontinue troubleshooting and contact a qualified HVAC technician.

Parts Commonly Involved

• Pressure switch – Verifies that the inducer motor has established proper draft before ignition.

• Inducer motor – Creates the airflow needed to safely vent combustion gases.

• Vent piping – Carries combustion gases outdoors and supplies combustion air where applicable.

• Condensate drain and trap – Removes condensation from high-efficiency furnaces; blockages can affect pressure readings.

• Control board – Monitors the pressure switch and records fault conditions.

When to Call a Technician

If Error Code 31 returns after completing the recommended homeowner checks, additional diagnosis is needed. A qualified HVAC technician can determine whether the problem involves the pressure switch, inducer motor, venting system, condensate drainage, or another component.

Call a qualified HVAC technician if:

• The error repeatedly returns.
• The inducer motor does not operate normally.
• The vent system appears damaged or blocked internally.
• The pressure switch or tubing appears damaged.
• Electrical testing or component replacement is required.

Safety Notice

Error Code 31 indicates that the furnace cannot verify safe venting conditions. Do not bypass or tamper with the pressure switch or its tubing. If the error continues after completing the recommended checks, have the furnace inspected before returning it to normal operation.

Manufacturer Documentation