If Your Pressure Switch on Your Furnace Keeps Faulting Out, What Could Be the Problem?

Pressure Tubes

• While there is some variation in how pressure switches manufactured by different companies look, most pressure switches have three wires: orange, yellow and blue. The blue wire is the closed wire, so if the pressure switch keeps tripping, this may be the source of the problem. Take out the blue tube and use a can of compressed air to clean out the tube, as there may be cobwebs or dust obstructing the tube and causing the airflow problem. Contact a furnace service expert if the tube cannot be cleared, as it will need to be replaced.

Blinking Error Code

• If an error light on the furnace's control board is blinking, the pressure switch may have tripped due to a bad control board connection or poor wiring. You can try to resolve the situation by disconnecting the power to the furnace and waiting a few minutes, then reconnecting the power. This may be enough to send a new electrical current to the power switch when the furnace turns on, resetting the switch. If the error code returns, however, you will need to contact a service professional for assistance.

Limit and Rollout Switches

• All rollout and limit switches should be closed and have sufficient energy -- 24 to 28 volts -- in order for the furnace to work properly. Open the furnace access door and push the reset button located in the middle of each rollout switch on the control board. Once you have reset the rollout switches, increase the heat setting for the thermostat and wait for the furnace to call for heat. If the furnace does not heat up or the pressure switch trips again, shut down the furnace and call a service professional.

Lock Mode

• Most furnaces are equipped with a safety lock feature that shuts down and locks the furnace once three unsuccessful attempts have been made to light the furnace. Once the furnace has entered the lock mode, you must manually reset the lock to turn the furnace back on. At this point, a professional furnace technician should inspect the furnace to determine if there is a problem with the airflow or heat exchanger, which can be a potentially dangerous situation if left unresolved. If you want to try one more time, however, you can find the component that looks like a light switch on the side of the furnace and turn it off and then on again. This will reset the limit control.