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How do I Check a Gas Furnace Draft Pressure Switch?

Posted Apr 7, 2017

A draft pressure switch is a device that is placed on a gas furnace as a safety measure. When a furnace is not receiving enough airflow, the draft pressure switch will stop the electrical current to the furnace, which will prevent the furnace from igniting. If your gas furnace is not working, there may be a problem with its draft pressure switch.

How to Check the Draft Pressure Switch on a Gas Furnace

1. Cut off the power to your furnace. To cut off the power to your furnace, you should turn the power switch on your furnace to the off position. You should also turn off the furnace’s power at the circuit breaker.

2. Find the draft pressure switch. You should be able to find the pressure switch by looking for the switch on the outside of the furnace. The switch is circular and bolted to the furnace; it should be located close to the draft inducer motor. A metal tube connects the draft inducer motor to the draft pressure switch.

3. Use a volt-ohm meter to check the amount of voltage going through the draft pressure switch. Begin by touching the tips of your volt-ohm meter’s prongs together to make sure the meter is at zero. Set your volt-ohm meter to 24 volts. Ground the volt-ohm meter by connecting the black probe to the furnace. Put the red probe on top of the metal tube that connects the draft inducer motor and the draft pressure switch.

4. Check the volt-ohm meter. The volt-ohm meter should have a reading of 24 volts or higher if the draft pressure switch is working correctly. If the reading on your volt-ohm meter is less than 24 volts, you should contact a heating and cooling company to check your furnace.

Other Problems That Can Prevent a Gas Furnace From Working

Many gas furnaces are meant to be replaced every 15 to 20 years, so a gas furnace that has stopped working may have simply reached the end of its lifespan. If a furnace stops working before it has reached the end of its lifespan, there are several things that may be the cause. Some of the most common reasons that a gas furnace stops working are a blocked pilot light, an overloaded motor, or a lack of gas.

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