What Is a Dishwasher Air Gap and Why Is It Important?

In more than 30 years as an appliance repair technician, I’ve seen hundreds of dishwashers stop working because of a mysterious gizmo called an air gap. And within five minutes, I can get these dishwashers working again.

That strange round silver R2-D2-looking thing, to the side of the kitchen faucet, is the dishwasher’s air gap. When it gets full of gunk from debris left on dishes, the dishwasher can’t drain. If it can’t drain, it can’t start. More than 60% of the calls I get from homeowners involve a dishwasher that doesn’t work because of clogged air gaps.

Most homeowners have no idea what the air gap is, and not all homes with dishwashers have air gaps. It really depends on what state you live in. Here’s what you need to know.

About the Expert

Scott Flint (aka Scott the Fixit Guy) has 30 years of expertise as an appliance tech and teacher, fixing washers, dryers, dishwashers, refrigerators, stoves and ovens. He has three YouTube DIY channels with more than 60,000 subscribers and an average of 1,000,000 views per month.

What Is a Dishwasher Air Gap?

It’s part of the dishwasher’s drain system. It’s about three inches tall, round and usually chrome (silver) or white.

What’s the Purpose of a Dishwasher Air Gap?

It allows air to mix with the drain water so it can easily flow away from the dishwasher. If there’s no mixing with air, it takes much more force for the drain water to move. (The other drain plumbing in your home has air gaps, too!) All brands of dishwashers can be set up to use air gaps.

How Does a Dishwasher Air Gap Work?

Air gaps bring in fresh air from the kitchen, filling the vacuum and equalizing air pressure, which allows the dishwasher to drain. As dirty water moves down the drain tube, it compresses air ahead of it and creates a small vacuum behind it.

Air gaps also prevent dirty water inside the sink’s garbage disposal from flowing backward down the drain tube, flooding the dishwasher.

In owner’s manuals, most brands offer two ways to install a dishwasher — one with an air gap, and one without. In the latter, the drain tube bends in a high upward arch under the sink, achieving the same effect as an air gap. The arch needs to be higher than the garbage disposal.

Do You Really Need an Air Gap for a Dishwasher?

Yes. You need some way to keep dirty sink water from flowing backward into your dishwasher, and some way to mix air with the drain water to help it flow.

You can avoid a clogged air gap by rinsing off your dishes before loading them.

What Are the Disadvantages of an Air Gap?

There are four disadvantages:

• An air gap is prone to clogging with food debris, which stops your dishwasher.
• It requires a hole to be drilled in the countertop or sink.
• Many people don’t like the way it looks.
• Installation is expensive, costing more than $200.

Which States Require Dishwasher Air Gaps?

In California, Washington, Minnesota and Hawaii, a dishwasher air gap is a mandatory residential plumbing procedure.

Here in California, I’ve had numerous customers ask me to install air gaps for them, because big box store contractors refuse to hook up a dishwasher without one. Check the building code for your area to see if an air gap is required.

A few years ago, I removed my dishwasher’s air gap and put a soap dispenser in its place. I bent my dishwasher drain tube in a high arch and secured it to the wall under my sink. It’s been working great ever since. But I know if we ever sell our house, I’ll need to reinstall that air gap to bring it up to code.

Why Is Water Coming Out of the Air Gap on the Dishwasher?

If you ever have water shooting out of your air gap into the sink, check the big black rubber drain hose that goes between the air gap and the garbage disposal. It’s likely clogged with food debris, or crimped somewhere so it’s no longer round.

There could also be a clog in the plastic tube on the garbage disposal where the air gap drain tube connects. Or the plastic plug that comes with a new garbage disposal hasn’t been removed, and drain water can’t enter the garbage disposal. These problems are all relatively easy to fix it.

How Do You Clear a Dishwasher’s Air Gap?

It only takes five minutes to clear a clogged dishwasher air gap.

• Lift the silver or white outer cover of the air gap straight up with a slight turning motion.
• Remove the air gap top piece by unscrewing or gently prying off the top with a flat-head screwdriver. The one that needs prying is more common.
• Now you’ll probably see the food debris clogging it. Remove the debris and set your dishwasher to drain. You should see a one- to three-inch column of water shooting straight up from the center hole of the air gap. If there’s just a dribble of water, go to the next step.
• With a straightened wire clothes hanger, go down around 10 inches into the center hole where you can see a little water coming out. Do this while the dishwasher tries to drain. Move the wire coat hanger up and down until you see the one- to three-inch column of water
• Put the cap back on.
• Put the silver or white cover back on with its front opening facing toward the sink.

You should now have a functioning dishwasher again, and you’ve avoided an expensive repair service call.