What Does Combustion Air Switch Failed To Close Mean?

Your combustion air switch is a safety mechanism that helps regulate combustion in your home to ensure it doesn’t go out of control. Combustion switches are so important because they can prevent fires from occurring and save you a lot of money on repairs. 

If you’re having any issues with your combustion air switch, this post is going to help you tackle them appropriately. The good news is that we’ll share some simple steps that you can easily implement without the need to hire a professional technician. 

Although it’s always recommended to consider hiring a technician to diagnose any combustion air switch issues, there are some DIY ways we’ll share here to help you out.

Importance of a Pressure Switch

The good thing about the air switch is that it offers safety against the removal of gases made in the combustion process of your house. Without the combustion air switch, they would be stored in the system and make their way back into your house, causing a backdraft. Backdrafts can cause lethal gases such as carbon monoxide to blend with the air supply in your house.

Fortunately, an air switch can stop the backdraft. It does this by checking your draft inducer motor to ensure it’s working correctly, and then it closes or turns on. But, if there is an issue with the draft motor, the air switch will fail to close or stick open. When that happens, then it shows there is an issue with the pressure switch.

Reasons Why Combustion Air Switch Failed to Close

There are several other causes of combustion air switch failed to close. When your switch encounters issues, chances are it might not be just one thing. You need to consider other factors before you realize the major issue that affected the air switch. Check out these issues below.

1. Vent Issues

If you have a blocked flue pipe, your furnace will experience problems vent out combustion gases. Therefore, this can cause your air switch to fail and refuse to close. If you have a damaged flue pipe, then you need to know that it’s not unusual. This is a common thing caused by debris such as leaves, dirt, and feathers, among other things. Ice or snow can also lead to clogging, so you need to care during the extreme winter season.

2. Malfunctioned Air Switch

The second thing that may cause your combustion air switch to encounter issues is if it has malfunctioned. One way to check if this is the case is by a multimeter. If you find out that the problem lies within the switch itself, you need to consider replacing it. But, ensure you turn the heater off before trying to replace it. You also need to disconnect all wires connected to the air switch. 

3. If the Air Switch Hose is Detached or Damaged

If the hoses are well connected, it’s easy for the air switch to tell whether the inducer motor works or not. However, if one or more of the rubber hoses break, develop cracks, or get detached for any reason, you’re likely to face a huge problem. This makes the air switch fail to close because it’s no longer getting a proper reading from the hose. 

How to Fix a Combustion Air Switch that Has Failed to Close

If your combustion air switch failed to close, the good news is that there is a way you can fix it. In this section, I’ll share some excellent tips that you can consider and implement to help fix your air switch.

Some of the things you need for the job include screwdrivers, a flashlight, a multimeter, and an air switch hose if it’s needed. Below are some of the steps to take during the repair process.

1. Turn Off the Power

Before you begin the fixing process, you need to turn off the power. You should do this by turning off the disconnect switch that you’ll find alongside the furnace. If there’s no disconnect switch close to the furnace, consider switching off the breaker in the house service panel or simply the breaker box. 

2. Thoroughly Inspect the Rubber Hoses

The second step involves thoroughly inspecting the rubber hoses. For that, you need to detach the main access panel at the front of the furnace. Then, take a closer look at the hose or the attached hoses on the air switch. Ensure they are well connected on both sides and that they are in good condition. 

Additionally, you need to carefully inspect the hoses to ensure they aren’t obstructed from the inside. However, avoid blowing into the hoses while connected since it can easily damage the switch. Therefore, consider using a cloth and a wire for cleaning. If you find that any of them has been broken, then consider replacing them.

3. Carefully Inspect the Port

Use the flashlight to inspect the port on the air switch carefully. Ensure they are completely clear without any obstructions. Once you confirm this, take your screwdriver and remove any debris you’ll see inside.

Ensure you do it carefully to avoid poking the air switch body and resulting in damages. You also need to remember you’re not supposed to blow into the inlet when taking out the debris. When you’re done removing the debris, reconnect the hoses.

4. Keenly Check the Furnace Cover

You also need to consider examining the ventilation slots on the furnace cover to make sure they are sparkling clean. If you check the furnace cover and find dirt and debris, make sure you remove it completely. You should also replace the cover.

5. Check the Vent Pipe for Any Obstruction

If you have a condensing type air switch, it’s important to inspect the venting pipe for obstruction. Usually, the vent pipe is made from PVC material, and it stretches throughout the roof of your home and into the sidewalls. 

6. Properly Test the Air Switch

Detach the wires which are connected to the air switch by removing the wire connectors from their terminals. Once you’ve done that, take your multimeter to test the air switch for any resistance. You need to touch the tester probe to any of the switch terminals and then record the reading. 

If the reading says 0 or close to 0, then there’s no resistance. This means that your air switch is in good condition. But, if the reading is higher than zero, then it’s important to consider replacing the air switch as soon as possible before it completely malfunctions. I would recommend calling a professional technician to come and replace it for you.

7. Appropriately Test the Furnace

Before testing the furnace, you need to reconnect the wires to the air switch and reinstall the access panel to the furnace. You should also fix the condensation trap to ensure the furnace gases are properly trapped. After doing all of that, turn on the power to the furnace to test its operation.

If you don’t see any errors, it shows the equipment is in perfect condition, and you can go ahead and use it. However, if you encounter any errors, it’s important to seek assistance from a professional.

What Is Air Proving Switch?

This a switch made from a die-cast aluminum body, and it contains no plastic or stamped tin parts. The good thing about this switch is that it’s durable and can detect small air pressures, vacuums, or changes in air pressure. 


As you’ve seen, many factors cause the combustion air switch to fail. Luckily, we’ve also shared some tips on how to fix the issue. So now you can solve combustion air switch problems on your own!

The good news is that anyone can do it. All the tips above are easy to follow, but you can also seek professional assistance if you find it challenging to do it yourself. 

If you have any questions, feel free to reach out through email, and I’ll be happy to assist however I can.