How It Works: Furnace Pressure Switch

Wondering how your furnace pressure switch works, and how to replace it? You’ve come to the right place. Read the blog below to better understand the importance of the furnace pressure switch, and find out how to remove and replace your furnace pressure switch. You can also watch the corresponding video for a visual how-to guide for replacing your furnace pressure switch.

What is a Pressure Switch on a Furnace?

As part of the furnaces ignition system, the pressure switch will close once the draft inducer fan motor reaches its maximum speed. This is a safety precaution to ensure that gas will not enter the furnace unless the toxic fumes within the burner assembly can be exhausted. If the draft inducer fan motor does not turn on or runs too slow, the pressure switch will not close, stalling the ignition sequence. A faulty pressure switch may be unable to close, preventing the ignition sequence from continuing.

You can use a multimeter to determine if there is a continuous electrical path present in the switch, provided the switch is connected to the furnace and the draft inducer fan motor is running. If there is no electrical continuity, the switch is failed and will need to be replaced.

Pressure switches are usually unique to each furnace model. You should enter the full model number of your furnace in our website search bar to find the specific pressure switch you need.

How to Fix Pressure Switch on Furnace

Before you replace the switch, first turn off the power to the furnace. We recommend shutting off the gas supply as well.

Pressure switches are normally located in the combustion chamber, close to the draft inducer fan motor. To reach it, you will need to uninstall the upper access panel. Disconnect the pressure switch wires, along with the vacuum tube or tubes. Next, unthread the mounting screw, or screws, to release the old pressure switch from the draft inducer fan motor housing or bracket.

When installing a new pressure switch you should confirm that the pressure rating matches the rating found on the original. Ratings will differ depending on your geographic location. Position the new switch on the fan motor, the housing or the bracket as required. Thread the mounting screw or screws to secure. Attach the vacuum tube or tubes, and connect the wires.

With the new pressure switch installed, replace the access panel. Turn the gas supply back on, as well as the power, and your furnace should be ready for use.

Watch our video on replacing your furnace pressure switch for a visual guide, or visit Repair Clinic for more furnace repair tips.

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