Residential heating systems are remarkably resilient to prolonged daily use, but things occasionally go wrong. One common issue homeowners face is a furnace pressure switch stuck open or closed, which causes the burner and blower to run inefficiently. We’ll help you troubleshoot common furnace pressure switch issues and identify the signs that it’s time to call the professionals for assistance!

What Does a Pressure Switch Do on a Furnace?

The furnace pressure switch is one of many safety mechanisms designed for home heating systems. The switch makes sure the furnace exhaust system drafts properly before the burner ignites. This prevents the build-up and release of carbon monoxide (CO) produced by the furnace’s natural gas or propane combustion.

What Does a Furnace Pressure Switch Look Like?

There are two types of furnace pressure switches available, and you can tell which kind you have based on its appearance.

  1. A mechanical furnace pressure switch looks like a spark plug in a car. Mechanical switches are cylindrical and typically two to three inches long. Their most recognizable feature is the operating piston, which reacts to furnace pressure changes. When pressure reaches a certain level, it contracts the piston to a point where it triggers an electrical signal that turns on the inducer fan.  
  2. An electronic furnace pressure switch measures furnace pressure using a piezo resistor, strain gauge, or capacitive sensor. Most electric switches are square or rectangular, and some have digital displays showing the current pressure within the system. The switch also releases an electrical signal when pressure reaches a pre-determined level.

Three Reasons Your Furnace Pressure Switch Is Stuck Closed or Open

There are several possible reasons why a mechanical or electronic pressure switch could be stuck open or closed. In many cases, these three issues are behind the problem.

1. Blocked Exhaust Vent

Blocking or clogging the exhaust vent will impact the amount of pressure that builds up in the system, causing the switch to stay in the open position. A complete blockage will cause your furnace to stop working entirely. Check the opening of your exhaust vents for debris, bird nests, or other obstructions, then see if your system works correctly.

2. Malfunctioning Suction Tube

Pressure switches detect negative pressure in the suction tube. A cracked or clogged suction tube won’t allow pressure to build up enough to trigger the pressure switch, leaving it in the open position.

3. Damaged Furnace Pressure Switch

Furnace pressure switches can wear out over time, causing malfunctions or unreliable readings. A faulty pressure switch may stay open or closed regardless of internal pressure conditions, increasing the risk of CO leaks and inhibiting overall system efficiency. If your local One Hour Heating & Air Conditioning® technician spots a bad switch, expect recommendations on furnace pressure switch replacement options.

Related Content: Why Won’t My Furnace Turn Off?

Two-Step Furnace Pressure Switch Troubleshooting

For most homeowners, replacing a furnace pressure switch requires professional assistance, but there are two important things you can do to triage the situation.

  1. Inspect the Exhaust Vent. As noted above, one of the most common causes of a pressure switch problem is a blocked vent. Inspect the exterior exhaust vent, remove debris, and try your system again.
  2. Inspect the Pressure Switch. Using your owner’s manual or an online resource from the furnace manufacturer, locate the furnace pressure switch and inspect it for signs of wear or damage. Electronic switches are often easier to inspect, as they may have a blank display or won’t react when you hit the “reset” or “test” button.

If you can’t detect any obvious issues with your visual inspections, it’s time to contact your local One Hour Heating & Air Conditioning® for a professional diagnosis. Remember, the pressure switch is a key safety mechanism. If you suspect it isn’t working, stop using your furnace immediately to prevent potential CO exposure.

Make The Switch to One Hour Heating & Air Conditioning®

For prompt and professional furnace pressure switch replacement and repair, look no further than One Hour Heating & Air Conditioning®. We provide fast, friendly HVAC services with a 100% satisfaction guarantee, so you know we’ll get the job done right. We’re ready to help; find a location near you or call 800-893-3523 to schedule an appointment today!