What To Do If Your Gas Furnace Pressure Switch is Stuck Open

Before we dive into why your pressure switch is stuck open, we should first talk about the purpose of this switch. Simply put, the job of this component is to monitor the pressure within the system. As your furnace powers up, the draft inducer motor will kickstart to create negative pressure within the furnace. This is to ensure the combustion gases are vented. You will typically find the furnace pressure switch in the OPEN position.

Once the switch senses pressure in the system, it then goes to the CLOSED position. This will allow it to complete an electrical circuit and move to the next stage of the starting process—turning on the burner and blower to create heat, then moving that heat throughout the home.



If the pressure were to remain in the system, the switch would stay open and the furnace wouldn't be vented. This ultimately means the furnace wouldn’t start up and work. As furnace combustion gases include dangerous carbon monoxide, improper ventilation can be deadly. If the system isn’t venting correctly, those harmful gases can stay in the unit, and even circulate through your home if the furnace starts up.

Given the dangers associated with a furnace, it’s a good idea to always be safe when handling this machinery. Before trying a DIY diagnostic or repair, always power off the system by using the switch on the unit. It looks just like a standard light switch. When you can’t find the switch, another option is to power down the system at the breaker box.

Pressure switch stuck open on furnace? If this problem is happening to you, there are a few possible culprits.

The pressure switch stuck open issue is usually caused by:

• Inadequate venting
• Broken furnace pressure switch
• Malfunctioning pressure switch
• Clogged pressure switch hose
• Disconnected pressure switch hose



Check out more information below:

If your furnace isn’t venting correctly, the pressure switch may be stuck open. This is often caused by a blocked flue pipe, which makes it hard for the system to eliminate combustion gases. The flue pipe can easily get trapped with leaves, feathers, dirt, and other debris. During the winter months, it can even get clogged with ice and snow.



One way to check out the venting situation is to simply look at your flue pipe. You can usually find it on your roof, or it may be on the side of your house. If you notice any debris inside, simply remove it if possible. Once removed, crank on your furnace to determine if the issue is solved. If the problem isn’t fixed, or if you can’t reach the debris in the flue pipe, call an HVAC technician for assistance.

If there’s a furnace pressure switch stuck open, it may be due to a broken or malfunctioning switch. Luckily, this issue is an easy fix. While we recommend calling an HVAC technician, the repair bill shouldn’t be that high. All they have to do is test the switch and replace it. While this can be a DIY project, it’s not recommended. Whenever you’re dealing with electrical components and combustion gases, it’s best to leave it to the professionals. If your furnace is installed or repaired incorrectly, it could make your home very dangerous.

Another common issue associated with a furnace pressure switch stuck open is when the hose is clogged or disconnected. The pressure switch hose is used to detect if the inducer motor is working properly. When the hose is damaged, clogged, or detached, the pressure switch can stay in the OPEN position.



As this problem can be fixed on your own, it’s better to call an expert. They will be able to tell where the issue is coming from, and they can also provide a quick, professional repair. While it’s easy to tell that the hose is broken or detached, fixing the problem is much more challenging.

When there’s a pressure switch stuck open on furnace, you can usually point to the causes above. However, there are a few other potential reasons for this issue.

Although less common, the switch may be stuck open due to:

Fresh air is needed for your furnace to work as it should. When enough air isn’t available, no combustion can happen. And after the combustion process, the combustion gases need to vent. If the air intake or exhaust is clogged with debris, the pressure switch can remain in the OPEN position. This is because blockages prevent the inducer fan from creating negative pressure.

A furnace pressure switch stuck open is a common problem for many homeowners. Be sure to follow the tips above to fix the issue and restore comfort to your home.