5 Ways to Fix a Dishwasher That Won’t Drain, According to a Plumber

published Dec 24, 2023
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A woman puts a plate in the dishwasher rack
Credit: Joe Lingeman/Kitchn

Dealing with dishwasher problems is stressful. Along with accumulating piles of plates, cups, and silverware in and around your sink, you’re tasked with figuring out what exactly is going on with your appliance (and, eventually, how to fix it). 

One common issue is a dishwasher not draining properly, resulting in standing water at the bottom of your appliance. This can happen for several reasons, and it’s important to pinpoint the correct issue so you can fix it. I asked Mark Snell, owner of Polestar Plumbing, how to diagnose the root issue of standing water. Below, he shares simple steps you can follow to figure out exactly why your dishwasher won’t drain — and what you can do to remedy each problem.

Why is there standing water in the bottom of my dishwasher?

When your dishwasher consistently has standing water after a cycle, the culprit could be one of many components inside the appliance or plumbing issues in another part of your sink. According to Snell, here are five of the most common potential causes for standing water in the bottom of a dishwasher.

Your dishwasher’s filter is clogged.

The filter or trap captures food particles and debris to prevent them from clogging the drain. It’s usually located at the bottom of your dishwasher, below the lower rack. “If the filter is extremely dirty or clogged, it can hinder the drainage process,” says Snell. To help prevent this from happening, preemptively clean your filter every few weeks, Jennifer Rodriguez, chief hygiene officer at Pro Housekeepers, previously told Kitchn. 

Credit: Volodymyr Bushmelov / Getty Images

Your drain hose is kinked or clogged.

If the filter isn’t the issue, Snell says it could be a problem with the drain hose that carries wastewater from the dishwasher to the water supply. A kinked, clogged, or improperly fitted drain hose — usually located under your sink or behind the dishwasher itself — can impede proper drainage, leading to standing water in your appliance. 

The air gap is blocked.

Dishwashers also have what’s called an air gap to prevent water from the sink from flowing into the dishwasher — it’s usually a chrome cylinder next to your faucet. Snell says you might experience drainage problems in your dishwasher if this part is blocked or malfunctioning. 

The garbage disposal is clogged.

If your dishwasher drain hose is connected to your garbage disposal, it can get obstructed. Food stuck inside the disposal won’t allow water to flow properly out from the dishwasher, which can lead to standing water. 

Snell says problems can also occur if the disposal is incorrectly installed. “If your dishwasher is connected to a garbage disposal unit, make sure the knockout plug inside the unit is removed,” he says. The plug is a small disc that covers the drain opening on the actual garbage disposal below your sink, and all you have to do is knock it out with a hammer and a screwdriver. (You can do this yourself with a tutorial if you’re confident; otherwise, call a plumber.)

Other dishwasher components are faulty. 

The drain pump, located inside the dishwasher, is responsible for expelling water from the dishwasher, so if it’s not functioning correctly, Snell says standing water may accumulate. 

Dishwashers also have a check valve under the filter that prevents water from re-entering the machine after draining. Damage to or blockage of this valve can also lead to standing water. 

Lastly, dishwashers are equipped with a safety feature known as the float switch, a part on the bottom of your appliance that monitors the water level. If this switch is faulty, it can hinder proper drainage.

How do you fix a dishwasher that will not drain?

Once you know what is wrong with your dishwasher, you can try to repair it. The fix you use for a dishwasher that’s not draining depends on the source of the problem. 

Credit: Joe Lingeman

If standing water has only happened once, it could be that you’re overloading your dishwasher (easy fix). “Too much in the dishwasher, or large items that obstruct the sprinkler, can lead to insufficient water circulation and stagnant water,” says Snell. Try loading fewer dishes per cycle and see if that resolves the issue.

If it’s an ongoing problem, follow the below steps to help diagnose the problem. Always consult your dishwasher’s owner’s manual for specific troubleshooting steps. 

Clean the filter.

Remove the filter from the bottom of your dishwasher by twisting it out. If it’s dirty or clogged, wash it thoroughly in the sink with water, getting rid of the largest debris. According to Rodriguez, you should soak the filter in hot water and dishwashing detergent and use a sponge or old toothbrush to get rid of all the dirt and food particles. Rinse the filter until it runs clear, and reinstall it before running another cycle. 

Unkink or clean the drain hose.

Before doing anything with the drain hose, disconnect the dishwasher from the power supply, a Bosch appliance website instructs. Once you’ve located the drain hose, see if it’s twisted. To unkink it, straighten it out, and have a bucket ready to drain the water into. With your hose secured and your dishwasher reconnected to the power supply, you can address a clog with a mixture of equal parts baking soda and vinegar into the bottom basket of the dishwasher (by the filter) and let it sit for 15 minutes, according to The Home Depot. Then, pour hot water into the basket and run the rinse cycle.

Credit: Sarah Crowley

Clean the air gap. 

When you find a clog in the air gap, Snell says to remove any debris causing the issue and then secure the plastic and chrome covers in place before running another cycle.

Unclog or clean the garbage disposal. 

You can tell if your garbage disposal is clogged if water drains slowly or accumulates in your sink, according to Snell. It might also have a foul odor. In that case, he says to run the water and turn on your disposal to try to remove the clog. For more stubborn clogs, you can also turn off and unplug the unit and try plunging away the clog, according to The Home Depot. If that doesn’t work, you should call a plumber. Remember: Never stick your hand down a garbage disposal!

Call a pro if needed.

If these steps don’t result in your dishwasher draining properly, then it may be time to enlist a professional to address other components of your dishwasher. In many cases, you should call a professional appliance repair technician. 

“But if your sink and drain pipes are also holding water, it’s possible that the issue is a clog in your home’s plumbing, in which case you’d need a plumber,” says Snell.