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

InterCounty Supply • Nov 04, 2021

Is the gas pressure switch stuck open on your furnace? If so, this is a common HVAC problem you’re experiencing. Luckily, finding a solution is typically pretty simple. While you may be worried you have a costly issue on your hands, the fix is actually affordable.


In this post, we’ll discuss what a furnace pressure switch is, how it gets stuck open, and how to find a trusted solution.

What’s a furnace pressure switch?

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.

Why does the pressure switch stay stuck open?

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:

Venting problems

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.

Broken or malfunctioning pressure switch

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.

Blocked or detached pressure switch hose

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.

Other possible causes

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:

Blocked condensate drain

Many furnaces out there have a condensate drain. As these can get clogged with debris, they can experience a blockage. When this clog occurs, it can cause a backup in the blower fan housing. This can lead to furnace pressure issues, including a furnace pressure switch stuck open.

Clogged air intake or exhaust

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.

Homeowner Looking For Reliable Heating, Cooling Or Plumbing Supplies?

Our dedicated specialists are standing by to help.

Most homeowners in need of new heating or cooling equipment will do an internet search to get information. Such a search will typically yield two results: what to buy or where to buy but not why to buy. At InterCounty Supply, as a wholesale supply house, we present all the options for what to buy and why it would be the best choice for YOUR situation. After all the options are presented a homeowner can decide for themselves what they need. ICS then has a licensed, factory trained contractor who SPECIALIZES in the equipment you need come to your home to provide the complete installation cost for the equipment you need. ICS will also handle all the paperwork for any rebates that are applicable.


Have questions, give us a call 914-939-4350 or fill out the form and one of our specialists will be in touch shortly.


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