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What Is a Furnace Pressure Switch?

Gas furnaces feature several safety devices, one of which is a pressure switch. The pressure switch works automatically when your furnace is running. You typically won’t see it, nor will you hear it. As a safety device, though, the pressure switch is an important part of your furnace.

Overview of the Pressure Switch

The pressure is a safety device in gas furnaces that’s designed to shut down the furnace in the event of insufficient pressure. Gas furnaces generate combustion gases. A blower known as a draft inducer will force these combustion gases out of the furnace and into an exhaust pipe. If there’s not enough pressure present, the pressure switch will shut down the furnace.

How the Pressure Switch Works

When your furnace turns on, the pilot light or ignition system will burn gas inside of the combustion chamber. At the same time, the draft inducer will force the newly generated combustion gases out of this chamber – as well as the heat exchanger – and into the exhaust pipe. It will create negative pressure inside of the combustion gases.

The pressure switch will remain in an open position by default. It will switch to a closed position, however, if the pressure is too low. Low pressure means that the combustion gases won’t be able to exit the furnace. And if the furnace continues to run, the combustion gases will accumulate inside of it.

Why the Pressure Switch Is Important

Combustion gases are a health hazard. Carbon monoxide, for example, is a byproduct combustion gas that’s created by all appliances that burn natural gas. With a pressure switch, you can rest assured knowing that carbon monoxide and all other combustion gases are being safely dispelled out of your furnace.

If the pressure switch is automatically shutting down your furnace, it usually indicates a pressure problem. Maybe the draft inducer has failed and is no longer blowing air, or perhaps the exhaust pipe is clogged with debris. Regardless, you’ll need to find out what’s causing the pressure switch to trip so that you can fix it. Replacing the pressure switch won’t solve the problem. Pressure switches are designed specifically to shut down furnaces in the event of insufficient pressure.

Of course, pressure switches can fail. Failure means that it won’t be able to automatically shut down your furnace if there’s insufficient pressure. Instead, combustion gases may build up inside of the furnace and potentially leak into your home’s interior.