What Happens When a Furnace Pressure Switch Goes Bad?

A furnace pressure switch is one of the most important parts of a furnace. It is a safety component that controls power to the system, and if it stops working, the furnace will not function. Read on to learn about what happens when a furnace pressure switch goes bad and how Hillsdale's furnace maintenance  team from Gladiator Services can help.

How Pressure Switches Work on Furnaces 

A furnace heating system has numerous components which, when functioning properly, keep your home at the perfect, warm temperature. When the temperature hits a certain degree, the thermostat signals the furnace to heat up. The inducer motor will kick in before the system ignites, creating a draft to ensure no remaining gasses are in the heat exchanger.

The pressure switch connects to the motor, and it senses changes in operation. It signals the motor to open or close the unit’s entry. 

As a crucial safety feature, the pressure switch automatically shuts the furnace down when it detects negative pressure to prevent back-drafting. Backdrafting occurs if the draft inducer motor lets exhaust fumes into the system, which can lead to combustion, fires, or in more extreme scenarios, explosions.

Signs of a Bad Pressure Switch 

On a gas furnace, the pressure switch is typically a standard component and will probably need repair or replacement at some point. Some of the most common signs of a pressure switch malfunction include: 

• There is no hot or warm air coming from your vents.
• Your furnace shuts down.
• Your furnace cannot function, even when turned on.
• An error code indicator light flashes on the circuit board.

Types of Pressure Switches

There are two types of pressure switches: electronic and manual. Additionally, pressure switches in different furnace types include: 

• Single-stage conventional furnace: includes one pressure switch and hose that connects to a draft inducer fan
• Single-stage condensing unit: includes one switch and two hoses
• Two-stage furnaces have two pressure switches: a high-pressure switch and a low-pressure switch 

What Causes a Furnace Pressure Switch Failure?

Like most electronic components, pressure switches have limited lifespans, and at some point, they meet their end. What happens when a furnace pressure switch goes bad? If the switch goes bad, you likely need a replacement to ensure the furnace can run properly. 

If your furnace is not working, the first thing to check is the pressure switch if the electricity is connected. Since it’s an automatic safety feature, your furnace will not function without it. 

A pressure switch going bad has no sole cause. Here are some common reasons it may occur: 

• Physical damage: Any type of physical damage, like cracks, on the unit’s diaphragm, can cause the pressure switch to stop working. Usually, you can see the damage upon inspecting the switch. 
• Age: Pressure switches can eventually go bad from wear and tear and environmental exposure after prolonged use.
• Debris: Though not common, debris can clog up a switch and force it to remain in its open position.
• Dirty diaphragm: If the pressure switch diaphragm becomes coated with filth, it can interfere with the switch’s sensors, inhibiting its function. 
• Damaged diaphragm: A busted diaphragm may make a flapping sound, similar to a flat tire.
• Blockage: A block in the port that connects the collection chamber can cause failure. 
• Damaged hose: Whether from age or a puncture, a pressure switch hose can receive damage, requiring it to need a replacement.

How to Test a Pressure Switch 

Testing the pressure switch is fairly simple, and you can often test it without needing a technician. First, disconnect the furnace’s power source, either through the disconnect switch or the circuit breaker. Then, check the following parts of the pressure switch:

• Examine the hose and look for holes or leaks; if you find any, the hose will need replacing.
• Check the hose port for damage or cracks, which will make it necessary to replace either the port, the switch, or both.
• Check the furnace cover for debris or dust obstructions, which can interfere with the pressure switch’s function.
• Check for ventilation pipe obstructions; this can cause a buildup of exhaust fumes in the motor, which will shut the pressure switch off.

Replacing a Pressure Switch 

The best way to find a replacement pressure switch is by contacting your system's manufacturer.  Another option is to look around online; you may find the right pressure switch through a contractor supply retailer. 

However, if you plan on having a technician do the replacement, it’s best to let them handle ordering the replacement part. Often, technicians will not use parts supplied by owners because: 

• Owners may unknowingly purchase the wrong part, model, or specification.
• What if the problem is not the pressure switch? Your problem may require a different solution not evident until inspection.
• There is potential for liabilities if something fails after installation when a tech uses parts they did not supply. 

Replacing a pressure switch yourself is possible if you are up for the challenge; however, we do not recommend it. Locating and ordering the correct part and replacing the old one is a potentially challenging ordeal. Instead, let a professional HVAC team take care of it for you.

We’re Here to Help with All of Your Heating Challenges

We hope you feel well-informed now that we’ve covered what happens when a furnace pressure switch goes bad. If you are unsure about evaluating your pressure switch or would prefer an experienced HVAC technician to take care of it, our team at Gladiator Services offers fast, reliable service throughout Bergen County, NJ, and the surrounding areas. We can handle the pressure switch testing, troubleshooting, and replacement to keep your home comfortable all winter long.



Our team can assess the issue and find a solution quickly and efficiently; we know how important having a warm, comfortable home is. Whether you have more questions about what happens when a furnace pressure switch goes bad or how furnace maintenance works, we are happy to help.

For further assistance on replacing a furnace pressure switch or troubleshooting a gas furnace with electronic ignition issues, contact our experts at Gladiator Services today at (201) 903-9784.