Informational Guide

Dishwasher Backing Up Into The Sink (Causes & How To Fix)

Dishwashers can cause various problems. This guide talks about how to deal with a dishwasher that keeps backing up your sink.

by Ian Haynes

Dishwashers are one of the most useful appliances to have at home, but they can cause many problems. Dishwashers attach to the water lines through your kitchen, so if something goes wrong with it, it can often cause problems in your sink.

Today, we will talk about how to deal with a dishwasher that keeps backing up your sink.

Why Does The Sink Back Up When I Run the Dishwasher? (And How to Fix)

Here are the most common reasons for your dishwasher backing up your sink and how to fix them.

Blocked/obstructed dishwasher

The most common cause of your dishwasher backing up into your sink is because your dishwasher is not draining properly. If the drain or filter of your dishwasher is clogged, then it can cause water to back up into the pipes and into your sink.

How To Fix:

Check the drain to make sure that it is not obstructed and also check the drainpipe to make sure that it is secured correctly and that there is nothing clogged in it. If there is a clog, you can remove it manually with a drain snake or with chemicals. Vinegar and baking soda can be poured down the drain and left overnight to loosen any clogs.

Jammed/slow garbage disposal

The problem could also be due to your garbage disposal. If the drain plug in the garbage disposal is clogged, then water may not run properly from your dishwasher. This can occur if you have an old garbage disposal that has not been cleaned in a long time or you have a new one that has not been installed correctly.

How To Fix:

In either case, clearing the blockage from the drain plug in the garbage disposal should fix the problem. If the problem persists, then your garbage disposal might be broken and needs to be replaced. You will know the problem is fixed if running your garbage disposal causes the sink level to lower.

Clogged kitchen sink

A clogged sink can also be the culprit. Your sink might be clogged, which can prevent the dishwasher from draining properly. A clogged sink can be dealt with in a couple of ways. You can run the garbage disposal to make sure that no food is blocking the drain, then snake out any physical clogs.

How To Fix:

You can buy a sink snake from your local hardware store. You can also use vinegar and baking soda to clear out and blockages in your sink drain. If none of these tricks work, then you might want to consider calling a professional to fix the issue.

Blocked kitchen sink air gap

When air gaps are working correctly, they prevent the sink from backing up due to water in the dishwasher. Over time though, food and grease can fall into the air gap and cause blockages. The result is that dishwasher water backs up into your sink. You need to clear this clog to get rid of the problem.

How To Fix:

Start by removing the cover and cap of the air gap and removing any material near the top. You can use a drain snake to get rid of anything that is further down in the air gap. You want to make sure there are about 2 inches of space to keep water from backing up.

Blocked drain plug

Lastly, the problem could be that the drain plug in your dishwasher is blocked. If the drain plug is blocked, then you should see standing water in your dishwasher. You can clear a blocked drain plug either manually or with a homemade solution of vinegar and baking soda.

How To Fix:

Pour your mixture into the basket at the bottom of the washer and let it settle for about 10-15 minutes. Once you have let it sit for a while, pour a pot of boiling water into the basket and see if it drains. Repeat if the clog still has not been fully cleared.


When to Call a Pro?

If none of our proposed solutions work, then it might be time to call a professional in to help resolve the issues.

Most of the time, you can fix a simple drain blockage on your own. But if the problem is due to broken components, like a cracked drain pipe or a broken valve piece, then your best bet might be to call a professional plumber.

You may also need to call a professional if the leaking has caused any extra damage to your kitchen.


Can I run my dishwasher if my sink is clogged?

If your sink is clogged, then running your dishwasher will likely cause a backup and overflow of water.

How do you unclog a dishwasher drain line?

You can unclog a dishwasher drain line either manually with a drain snake or chemically with a mixture of vinegar and baking soda.

How do you use vinegar and baking soda to unblock a dishwasher?

Pour in the baking soda first, then let it settle. Next, add in the vinegar slowly until you see the frothy mixture bubble up. Don’t put the vinegar in too quickly, or else it will likely start to spurt when it reacts with the baking soda. Then, flush out the mixture with a pot of boiling water.

Can sewage back up into the dishwasher?

If sewage backs up into your dishwasher, this could mean that there is a backup in the main sewer line. Blocks in your main sewer line should be handled by a professional.

Can you put drain cleaner in the garbage disposal?

Yes, you can use drain cleaner in the garbage disposal. Make sure you read the instructions on the drain cleaner, so you know what kinds of materials it is safe for.

Can I pour boiling water into the dishwasher?

Yes, boiling water will not hurt your dishwasher and is actually one of the better ways to fix clogs in the filter and drain.

How much does it cost to replace a dishwasher drain pump?

A typical dishwasher pump costs anywhere between $100-$300 to replace. Replacing a higher-end model may take above $400. In many cases, you may want to compare the price of purchasing a new dishwasher to the repair. 

purchasing a new dishwasher


No doubt that your dishwasher backing up into your sink is a frustrating problem to deal with. It’s better if you fix the issue sooner rather than later, so take steps now and save yourself a headache in the future.

And if you're in the market for a new dishwasher, check out our article on the quietest dishwashers available.

Ian Haynes is an expert writer who has successfully deployed over 500 plumbing pages and other related content. He has an excellent understanding of home plumbing issues and translates his experiences via Plumbing Lab so readers can have a better understanding of common household problems. Outside of his work, Ian likes exploring Brooklyn with his Labrador.