3 Reasons Why Dryer Booster Fan Is Not Working

A dryer booster fan is an essential component of your dryer, particularly if you have a long length of ductwork running from your dryer to outside of your home. A dryer booster fan creates more airflow in the dryer ductwork, which leads to more efficient drying.

Dryer booster fans are pretty simple devices, but there are a few things that can cause them to stop working. Usually, the problem lies in a faulty switch, but it’s also possible for the problem to be caused by a buildup of lint in the fan, or because the fan’s motor has failed.

In this article, we’ll be taking a quick look at how dryer booster fans work, and we’ll also go over the various problems that can affect your dryer booster fan and show you how to deal with them. 

How Does My Dryer Booster Fan Work?

Like we mentioned, dryer booster fans are necessary to have if you have a lot of ductwork connecting your dryer to the dryer vent outside your home . This is because the air, moisture, and bits of lint in your dryer’s exhaust have a harder time exiting the dryer when the ductwork is too long, which makes your dryer less efficient and your drying times a lot longer.

A dryer booster fan generates increased airflow within your dryer’s ductwork, which helps move your dryer’s exhaust and all the moisture/lint in it through the ductwork more easily. Dryer booster fans are usually installed somewhere along the length of the ductwork.

Dryer booster fans connect to your home’s power supply via a standard electrical outlet and are designed to come on automatically when your dryer is running. This is done through the use of one of two types of switches, either a pressure switch or a current relay.

A pressure switch works by sensing when there is increased pressure in the ductwork, which happens when the dryer is on and exhaust is coming from it. It switches the fan on when it detects increased pressure and switches it off when the pressure goes back to normal.

A current relay is basically the same sort of thing, except instead of detecting when the exhaust is going through the ductwork, it detects when the dryer is on and receiving power. When it detects that the dryer is using electricity, it turns on the dryer booster fan as well. Pretty simple stuff.

Other Things to Know About Your Dryer Booster Fan

If this is your first time installing a dryer booster fan in your home, there are a few things you should know beforehand. Let’s quickly go over some of these things now.

One important thing to remember is to not install your dryer booster fan too close to the dryer itself. This is because if the fan is too close to the dryer, the suction from the fan can pull excess lint into the ductwork, which can clog up the fan if enough gets in there. 

Related: Do Dryer Booster Fans Really Work?

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In general, you should try and install your dryer booster fan at least 15 feet away from your dryer itself, but if you have no choice but to install it closer, you should consider installing a lint trap to make things easier on yourself.

As for when it’s a good idea to install a dryer booster fan in the first place, this depends on how long your dryer exhaust ductwork is as well as how many bends are in the ductwork.

For straight lengths of ductwork that are 25 feet long or more, a dryer booster is probably necessary. For each bend in the ductwork, however, shorten that length by 5 feet. Therefore, if your dryer exhaust ductwork has two bends in it, the maximum length it can be before you’ll need a dryer booster fan is 15 feet.

How to Fix Your Dryer Booster Fan

If your dryer booster fan isn’t working, the correct method of fixing it depends on the reason why it’s not working to begin with. Let’s check out some of the common issues that affect dryer booster fans and explain how to fix them.

Failed Pressure Sensor

The pressure sensor usually consists of a sensing line made of vinyl that connects to a circuit board via a diaphragm. When the dryer starts running, the positive air pressure flows through the sensing line and expands the diaphragm, which in turn causes a circuit to close. The closing of the circuit is what turns on the dryer booster fan.

Why It Fails:

There are a few reasons why your pressure sensor might fail, and not all of them have to do with your pressure sensor itself. If there’s a leak in the ductwork before the sensor or if the ductwork is clogged with too much lint, it can mess with the sensor’s ability to detect differences in air pressure.

There may also be problems if moisture from the dryer manages to get into the sensing line. The line needs to be clear of any obstructions to sense pressure properly, so water or anything else in the lines can screw everything up.

It’s also entirely possible that the sensor may not be calibrated correctly to begin with. Some pressure sensors are made with leaks built in to prevent too much pressure from accumulating within the sensing lines, but these don’t always work the way they’re supposed to.

How to Fix:

Depending on what is causing the pressure sensor to act up, the solution to fix it will vary. If the ductwork is leaky, you can solve the problem by patching it up with some aluminum tape. If the ductwork is clogged with lint, clean the lint out and see if that solves your problem.

If neither of those work, try inspecting the sensing lines and see if there’s water or other unwanted stuff in there. If so, cleaning out the sensing line might solve your issue.

You can also try getting rid of the pressure relief leak in the sensing line. The leak is usually in the form of a T-connector attached to the sensing line. Remove the T-connector and plug the sensing line directly into the circuit board, and see if that works.

If all else fails, your sensor is probably broken and you’ll have to have a new one installed.

Failed Current Relay

The current relay is a type of switch that senses when power is running through it and turns itself off and on based on that. This type of switch is called a solid-state relay, meaning that it contains no moving parts. This makes solid-state relays more reliable than mechanical relays.

Why It Fails: 

Despite their reliability, current relays can still fail after a period of time. This usually happens if an abnormal current is applied to the relay, which shorts it out. When this happens, the dryer booster fan will completely fail to turn on.

How to Fix:

Unfortunately, if your current relay fails, there’s nothing you can really do about it except replace it. 

Excess of Lint in Dryer Booster Fan

Lint is tiny fibers that separate from your clothes when they get tumbled around in your dryer. Most of the lint gets caught in your dryer’s lint trap, but a small amount of it is often able to get through.

Related: Why Does Dryer Vent Keep Getting Clogged?

Why It Fails: 

If enough lint gets through your dryer’s lint trap, it will start to accumulate within your dryer’s ductwork, including in the dryer booster fan. If there’s too much lint stuck inside the fan, it won’t be able to generate a sufficient amount of airflow.

How to Fix:

You can easily fix this issue by periodically cleaning out your dryer booster fan.

In most cases, cleaning your fan should be pretty simple. Remove the ductwork connecting the dryer to the fan (after making sure to unplug the fan first). Then, just pull out all of the lint you find in there.

It’s also a good idea to shoot some compressed air into the fan intake to get rid of any remaining lint bits you might have missed.

Broken Fan Motor

Dryer booster fans are always powered by an electric motor. This is obviously the main component of the fan, and the functionality of the motor is paramount to the functionality of the entire fan.

Why It Fails:

Since the motor has moving parts, it’s inevitable that it will wear out at some point. In particular, the motor contains several bearings, which will eventually seize up after the fan has been run for long enough.

How to Fix:

If your fan motor breaks or the bearings fail, there is, unfortunately, no real way to repair it. You’ll have to buy a new motor assembly if you want to solve this issue. 


Dryer booster fans are pretty simple devices and don’t malfunction too often, but like any device, there are always a few things that can go wrong. We hope that the information we’ve shared with you today will make it easier for you to diagnose any problems with your dryer booster fan and maybe even fix them yourself. 

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