Combustion Air Switch Failed To Close? (Possible Causes & Fixes)

Upgraded Home Team
by Upgraded Home Team

The furnace pressure switch, aka air switch, is a safety measure device found near the draft inducer motor. Its job is to ensure that the furnace only works when the venting air pressure is appropriate.

So, if the display shows this error ‘combustion air switch failed to close’, chances are that your furnace isn’t functioning at all. The good news here is that air switch fails are easy to fix.

Inspect the flue pipe for debris and clean it out if there is a blockage. A combustion air switch can fail if the air hose detaches, and you’ll need to reattach it. Turn off your heater and replace the air switch if it is outdated or broken.

Read on through this guide to learn more about the ‘combustion air switch failed to close’ error, and learn ways to fix it once and for all.

Related Content: Main Parts Of A Furnace | Furnace Brands To Avoid | Pressure Switch Open With Inducer On? | Why Is My Goodman Furnace Pressure Switch Stuck Open?

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Why Is A Pressure Switch Necessary?

The air switch is a safety device that aids in the removal of gases made in the combustion process from your house. Without it, they’d be stored in the system and may even make their way back into your home, that’s known as backdrafting.

What Kind Of Damage Can Backdrafts Do?

It can cause lethal gases such as carbon monoxide to blend with the house’s air supply. According to one stat, 784 people died in 2009 due to the exposure to these lethal gases in the US.

How Air Switch Stops Backdrafts?

Your draft inducer motor draws dangerous gases from the heat exchanger with the help of a flue pipe. The air switch checks your draft inducer motor to ensure it’s working correctly, and then it closes, i.e., turns on.

However, if there happens to be a problem with the draft motor, the air switch will stick open or fail to close. It means there’s a problem with the pressure switch or some other furnace part that you should address as soon as possible.

HVAC Pressure Switch Opened Or Closed

Other Causes Of The ‘Air Switch Fail To Close’ Error

The most likely causes for your air switch’s failure to close are:

Obstructed And Clogged Venting

If the flue pipe is blocked, your furnace will likely face problems venting out combustion gases. As a result, it can cause your air switch to fail and remain open.

An obstructed flue pipe isn’t unusual. It happens all the time due to debris such as dirt, leaves, feathers, and others. In fact, it can also get clogged with snow or ice during extreme winter.

Damaged Or Detached Air Switch Hose

The air switch can quickly tell if the inducer motor works fine as long as the hoses are adequately connected.

For any reason, if one or more of the rubber hoses break, develop cracks or holes, or get detached, you may face a problem with your air switch. Since it no longer gets proper reading form the hose, it fails to close and thus remains stuck open. Later on, we’ll tell you how to check and fix it.

Malfunctioning Air Switch

The problem may lie with your air switch itself. You can check your air switch by multimeter and replace it accordingly. Make sure you turn the heater off before trying to do that.

Disconnect all the wires connected to the air switch – pull off the connectors from the switch terminals before proceeding further. We’ll tell you all about how to resistance test the air switch, further down below.

Equipment/Tools You Need To Fix The Air Switch

Ready to troubleshoot your combustion pressure switch? Here are a few things you’ll need:

  • Multimeter
  • Screwdrivers
  • Flashlight
  • Air switch hose, if required

How To Fix A Combustion Air Switch That’s Failed To Close

By now, you should have a fair idea of what goes into troubleshooting and fixing this error. Once you have gathered the necessary tools, it’s time to fix the pressure switch that’s stuck open.

Here’s a step-by-step guide to fixing pressure switches that fail to turn on. Let’s get started:

Step 1: Turn The Power Off

Before proceeding with the operation, switch off the power by turning off the disconnect switch placed alongside the furnace. If you don’t see any disconnect switch near the furnace, switch off the breaker in the house service panel or breaker box.

Step 2: Examine The Rubber Hoses

Detach the main access panel at the front of the furnace. Now, look at the hose (or hoses) attached to the air switch. Make sure that they are properly connected on both sides and in a good state.

Also, carefully inspect the hoses to ensure that they aren’t obstructed from within. But don’t blow into the hose(s) while connected, as it can damage the air switch. Instead, use a cloth and a wire switch to clean them thoroughly. If any of them are found broken or loose, replace them stat.

Step 3: Inspect The Port

Use the flashlight to check the insides of the hose port on the air switch. Make sure they look clear with no obstructions of any kind.

Now, take the screwdriver and remove all debris you find within. Do it carefully as you don’t want to poke the air switch body. Again, don’t blow into the inlet s) to take out the debris or other obstructions. Reconnect the hoses when done.

Step 4: Check The Furnace Cover

Examine the ventilation slots on the cover of the furnace to ensure they’re clean. However, if you find dirt and debris, remove it. Then, replace the cover.

Step 5: Inspect The Vent Pipe For Obstruction

If the air switch is of a condensing type, then you need to scrutinize the vent pipe for any blockage. Typically, the vent pipe is made from PVC, and it stretches out all through the roof of your home or into the sidewalls.

Step 6: Test The Air Switch

Detach the wires connected to the air switch by removing the wire connectors from their terminals. Grab your multimeter to test the air switch for resistance.

Touch the tester probe to any of the switch terminals and record the reading. If it’s 0 or near to 0, there’s no resistance, and your switch is in perfect working order.

However, if the reading is higher than zero, then you need to replace the air switch ASAP as it is malfunctioning. Don’t replace it yourself. Let a professional technician handle the job.

Step 7: Test The Furnace

Remember to reconnect the wires to the air switch and reinstall the access panel to the furnace. Also, fix the condensation trap so that you can be sure that the furnace gases are being trapped.

Now, please turn on the power to the furnace and test its operation. Hopefully, you won’t see the error again and find the equipment to be in perfect working order.

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The Bottom Line

It is crucial to understand that trying to complete this repair on your own can be dangerous. Incorrect installation of a pressure switch can damage your furnace and also lead to possible safety issues for your home.

Instead, call on expert technicians to fix the problem for you. By scheduling a furnace repair, you’ll have the peace of mind that a professional did the right job.

Upgraded Home Team
Upgraded Home Team

We are a team of passionate homeowners, home improvement pros, and DIY enthusiasts who enjoy sharing home improvement, housekeeping, decorating, and more with other homeowners! Whether you're looking for a step-by-step guide on fixing an appliance or the cost of installing a fence, we've here to help.

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