Fixing a Pressure Sensor Switch

Updated on February 26, 2019
JesseUnk profile image

As I fix things up in my own home I share them here. I love to share my successes with others so they can improve their homes as well.

Furnace Kicks on but No Heat Blows Out

The heat is on, but the temperature keeps dropping!
The heat is on, but the temperature keeps dropping!

What Does it Mean When the Furnace Light is Blinking?

Just last night I awoke from a nap with my wife to find our house to be about five degrees colder than the thermostat was set for. I could hear the furnace continuing to kick on, but no heat was coming from any of our vents. I'm not much of a handyman, and certainly am not an expert in HVAC, so I called my uncle who happens to work in the HVAC profession. A day later I was able to fix my furnace myself with his simple instructions.

What Would Cause a Furnace to Not Kick On?

The back panel of your furnace should come off and expose a series of parts and wires that you will be able to access.
The back panel of your furnace should come off and expose a series of parts and wires that you will be able to access.

3 Blinking Lights on Furnace

You can see the small red bulb that indicates many different series of blinking lights that can mean multiple different errors. The black button above activates the furnace when it is pressed in by the metal doors.
You can see the small red bulb that indicates many different series of blinking lights that can mean multiple different errors. The black button above activates the furnace when it is pressed in by the metal doors.

How to Troubleshoot a Pressure Sensor Switch

I opened the back of my furnace and saw that the small red bulb was blinking 3 times before stopping and repeating again. On the furnace door, you'll see a sheet of paper that has various codes and what they mean. 3 blinks means there is an issue with the pressure sensor switch. This can occur for various reasons, whether that's your exhaust vent is blocked by a birds nest, a strong wind gusted in and messed up the sensors, or the sensor needs to be replaced. If it's simply a sensor issue then you can flip the breaker attached to your furnace and wait about 30 seconds. When you flip it back on everything should be right as rain! The same goes for your blocked vent. If you find the blockage you just need to clear it and your furnace should right itself shortly after.

Pressure Switch Sensor Issues

How to Test a Furnace Pressure Switch

Another way to check your switch is to take the hose from your pressure switch and gently as if you were going to whistle, suck on the end. You should hear a small click sound and another click when you take your mouth from the hose. If you don't hear that sound you need to replace your pressure sensor. If the hose appears to be brittle, cracked, or has any cuts or tears then you will need to replace your hose as well.

How to Replace a Pressure Switch Sensor

Click thumbnail to view full-size
Simply remove the screws holding the piece in place, and connect the wires to the new piece. Slide the hose over the knob and you're done!Furnace will light up as soon as you put the doors back on.
Simply remove the screws holding the piece in place, and connect the wires to the new piece. Slide the hose over the knob and you're done!
Simply remove the screws holding the piece in place, and connect the wires to the new piece. Slide the hose over the knob and you're done!
Furnace will light up as soon as you put the doors back on.
Furnace will light up as soon as you put the doors back on.

Replacing a Furnace Pressure Sensor Switch

Replacing a pressure sensor switch is so simple that my uncle who works in HVAC simply told me, attach the new piece the same way the old piece was attached and it should work. When you look at the piece you need to take the hose off, remove the two wires attached to the back, and remove the screws that hold it into the side of the furnace's metal. Grab your new sensor and screw it in. You'll need to check the back of the sensor to see which plug is positive and negative, and that's about the extent of the difficulty of the repair. Once you check it and plug it in you'll need to connect your hose. Once you have it in and secure, you can press the black button mentioned before and in a few seconds you should see the furnace begin to glow and a burst of flame will emerge and start to warm your home. If it does not light, you'll need to search for other options.

How to Get the Furnace Working

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The initial glow of the furnace.Final product as the house slowly becomes warm again!
The initial glow of the furnace.
The initial glow of the furnace.
Final product as the house slowly becomes warm again!
Final product as the house slowly becomes warm again!

How to Know Which Sensor to Use

You will need to make sure whatever sensor you buy is one that fits your model of furnace. To check this there should be a model number posted among many other things on the inside or outside of your furnace. Mine was inside the furnace, just to the left. You can call your local supplier, or even purchase your sensor on Amazon or eBay. Once you get the correct part, the replacement is as simple as 1, 2, 3.

In conclusion, even a person who is just starting to learn about home improvement can fix a pressure sensor on their furnace. Because of my uncle's information, I was able to avoid a service fee to a local repairman that would have probably been far more expensive than what the 5 minutes of work would have been worth.

How to Find My Furnace Model Number

The model number can be identified in the upper right hand corner of the information sheet.
The model number can be identified in the upper right hand corner of the information sheet.

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This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

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    © 2019 Jesse Unk

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