Furnace Pressure Switch Stuck Open/Closed

One of the most important safety features on a furnace is called a pressure switch. You may have heard people refer to open and closed switches and do not understand what that means. Here, we discuss what to do if the furnace pressure switch is stuck open or closed. Understanding your heating and cooling setup is vital to maintaining it.

How Does a Furnace Pressure Switch Work?

pressure switch stuck open or closed test

The pressure switch senses pressure within the furnace. It is normally open, and when the furnace starts, it senses the negative pressure that occurs when combustion gases are vented properly. Once it senses that negative pressure, the pressure switch changes to the closed position. This completes the electrical circuit and allows the furnace to proceed to its next stage.

If the pressure switch doesn’t sense that negative pressure, then it shuts the furnace down.

Furnace Pressure Switch Stuck Closed

One way to know if the pressure switch is stuck closed is if the blower fan will not startup. You might be getting an error code that indicates the problem is with the pressure switch. The tell-tale sign is found by disconnecting one of the wires (making the position open) from the pressure switch. If the blower fan initiates, then you know the pressure switch needs replacement.

Before you buy and install a new switch, give the stuck switch a tap to see if that knocks a screw loose. Sometimes that will do the trick (but may not be a very permanent solution).

Furnace Pressure Switch Stuck Open

First of all, the pressure switch may not be stuck. It might be doing its job. It’s in the open position either because the pressure switch is faulty and needs replacement, or there is something wrong with the venting or intake in your HVAC system. In order to test this, you need to bypass the furnace pressure switch.

Once again, the fix might be just to replace the switch. If the pressure switch is working, then the most likely culprit is an obstructed vent. Check your exhaust vents, specifically the vent cap, and look for problems (snow, bird’s nest, etc.).

Buy HVAC Switches Online

If you need to replace your pressure switch, then PlumbersStock is a great place to start. We carry a variety of HVAC switches, as well as an enormous inventory of HVAC parts. Did you know that you can find member pricing here on certain items (typically name brand, MAP priced items) if you log in? For industry professionals buying in bulk, please consider contacting us directly for extra special pricing and extra savings.