Furnace Pressure Switches

White family in the kitchen in Olathe

A family gets breakfast in kitchen in winter.

What Is a Furnace Pressure Switch?

The furnace has a number of mechanisms that allow it to run safely and efficiently. One important component is the pressure switch. The pressure switch is triggered when it senses what’s called backdrafting. Backdrafting is when exhaust fumes reenter your system. Your pressure switch can also sense other failures, such as a gas leak or a mechanical problem. When the switch senses the hazard, it will automatically shut off your furnace to prevent further damage.

What Does It Look Like?

Typically, the switch will be a disc-shaped metal component connected to a hose. Standard furnaces operate with a single pressure switch. However, depending on your furnace, you may have more than one. Condensing furnaces will have two hoses, while two-stage furnaces have two entirely separate pressure switches. Modulating furnaces can even contain up to three.

What Are Some Common Problems With Furnace Pressure Switches?

Furnace pressure switches are an important feature for keeping you safe. However, malfunctions with the pressure switch can incur false positives, which cause your furnace to shut down.

Here are four commonplace errors that our Smith Service customers have experienced with their pressure switches:

1. The pressure switch is jammed shut.
This can be caused by moisture buildup, among other issues. If the furnace detects the switch is shut, it will not run. Typically, your technician will replace the pressure switch if this is the case.

2. The inducer motor fails.
The inducer motor’s role is to blow harmful exhaust out of the furnace. When this doesn’t work, the pressure switch can’t properly expel the fumes, so your furnace will stop operating. Your technician will test the voltage to see if the inducer motor is working, and if it’s not will replace it.

3. The furnace won’t ignite.
In some cases, the ignition mechanism can fail due to a bad pressure switch. If the mechanism gets stuck open, this blocks the furnace from igniting the pilot light, as well as turning on the blowers. However, this could also be a sign of an internal error that is unrelated to the switch.

4. There’s frost buildup.
Frost can develop when moisture from the exhaust mixes with cool air. Over time, the inside of the intake pipe becomes constricted, causing your furnace to shut down. Your technician will clear out the frost. He or she may also extend the exhaust vent and remove obstructions to prevent the issue from happening again.

Remember, your pressure switch is there to protect you! Keeping it in good shape will protect you from harmful gases and keep your furnace running. Call The Smith Service Company, Inc., today at 785-594-8800 if you need to schedule a repair for any make or model of heating system. In addition to repairs, we offer maintenance and installations for the residents of Baldwin City, KS, and surrounding regions.

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