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

Dec. 17, 2019

If your furnace is showing a pressure switch error, it can be concerning. The good news is that usually, an open pressure switch error isn’t an extremely extensive (or expensive) fix. 
Possible reasons your furnace pressure switch is stuck open include:
  • Obstructed venting 
  • A disconnected or damaged pressure switch hose
  • A malfunctioning pressure switch 
Below, we’ll go into more detail about what a pressure switch does, as well as the issues above that can cause the pressure switch to stick open. 

If you’d rather have an expert come and take a look at your furnace, we’d be happy to help. Regardless of the specific issue, we can accurately diagnose your unit and make any necessary furnace repairs.

Schedule furnace repair
 

What is a pressure switch and what does it do?


Your furnace’s pressure switch is a safety feature that ensures the gases created in the combustion process exit your home and aren’t reintroduced into your system—an issue called “backdrafting”.

Backdrafting can cause the dangerous gases created in the combustion process (like carbon monoxide) to enter into your home’s air supply. Backdrafting can also cause small explosions in your heat exchanger, the core of your furnace. 

Here’s how your pressure switch prevents backdrafting:
  1. Your furnace creates gases (some of which are poisonous) during the heat-creation process.
  2. The draft inducer motor sucks those gases out of your heat exchanger and out of your home via a flue pipe.
  3. The pressure switch monitors the draft inducer to make sure it’s properly getting rid of those gases. If the draft inducer is working properly, your pressure switch will close to complete the circuit  (or “turn on”).
  4. If there is an issue with your draft inducer motor, your pressure switch will open (or “turn off”), shutting down your furnace down by preventing it from igniting.
So, to some degree, an open pressure switch is a good thing...it means your furnace’s safety features are working (and preventing dangerous gases from entering your home).
However, if your furnace is showing you an error saying that the pressure switch is stuck open or staying open, you likely have an issue with the pressure switch itself or another part of your furnace. 

Let’s look at what can cause your pressure switch to stick open, below. 
 

What can cause your pressure switch to stay stuck open? 


The most likely reason that your pressure switch is stuck open is due to:
  • Obstructed venting (chimney/flue pipe) 
  • Disconnected or clogged pressure switch hose
  • Malfunctioning pressure switch 


1. Obstructed venting:


If your furnace’s flue pipe is obstructed, your system will have trouble getting rid of combustion gases, which can cause the pressure switch to stay open.

A clogged flue pipe isn’t that uncommon, as flue pipes can become clogged with debris like leaves, dirt, feathers, etc. or can become frozen or clogged with ice and snow during the winter.

To check your furnace’s venting, simply take a look at your flue pipe. The flue pipe will either be located on your roof (if you have a conventional furnace) or will be a white PVC pipe located on the side of the house (if you have a conventional furnace).

If you notice debris that is easy to reach, simply clear it away and turn your furnace on again. If this doesn’t solve the issue, you should reach out to a technician. There could be a clog farther down in your system that’s preventing your furnace from getting rid of those combustion gases. 


2. Disconnected or damaged pressure switch hose


The pressure switch is able to tell whether the inducer motor is doing its job via a hose. If this hose is damaged (cracks, holes) or disconnected, it can cause the pressure switch to get an inaccurate read and stick open. 

While this is something you can check and potentially fix on your own, we would suggest calling a professional to come to take a look. It should be fairly easy to tell if the pressure switch hose is disconnected from the inducer draft blower, but reattaching it can be more difficult. 

If for some reason the hose is damaged, a technician should be able to quickly (and inexpensively) replace the hose. 
 

3. Malfunctioning pressure switch 


If you didn’t notice any obstructions in or on top of the flue pipe and you checked that the pressure switch hose was connected, you may just have an issue with your pressure switch. 

A technician will test your switch with a digital multimeter and replace it if necessary. 

This is another repair that you can complete on your own, but we wouldn’t recommend it. If this part of your furnace is installed incorrectly, it could cause long-term damage to your furnace and potential safety issues for you and your household. 
 

Still having issues with your furnace pressure switch? Contact a team of (Air) Experts!


If you think you’re experiencing one of the issues listed above (or think something else is wrong with your furnace), you likely need an experienced technician to fix it. We have over 25 years of experience helping New Jersey homeowners with all of their furnace issues, and we’d be happy to help you too.

Schedule furnace repair