Dishwasher Not Draining? Common Causes and How to Fix Them

You open the dishwasher at the end of a cycle and find an inch of cloudy water sitting in the bottom. It is a common problem, and it usually shows up at the worst possible time. The dishes are not clean, the smell starts to build, and it is not obvious whether the issue is the appliance or the drain.

The good news is that a dishwasher that will not drain is often a simple blockage rather than a failed appliance. Food particles, grease, a kinked hose, or a disposal connection can all stop the water from leaving. A few of the possible causes involve the drain pump or check valve, which are more involved, but most can be diagnosed in order from the easiest to the hardest.

This guide walks through the safe way to investigate, the most common causes, and when the repair should be handed to a plumber or appliance technician.

Safety First: Shut Off Power and Water

Before reaching into a dishwasher, always remove the power. Turn off the dedicated breaker that feeds the dishwasher, or unplug the unit if the cord is accessible. Water and electricity are a dangerous combination, and the heating element can be hot even after a cycle ends.

Also close the water supply valve, which is usually located under the kitchen sink. Wear gloves, and use a cup or sponge to remove standing water before working, so you can see the components. Never leave standing water in contact with an open electrical connection.

How a Dishwasher Drains

Understanding the path water takes makes the troubleshooting easier. At the end of the wash and rinse cycles, a small drain pump pushes water out through a flexible drain hose. That hose typically runs up to a high loop under the counter or to an air gap on the sink, then down to a garbage disposal or a sink drain tailpiece, and finally into the P-trap.

A blockage anywhere along that path will leave water in the tub. Because the dishwasher shares the drain with the sink and disposal, a problem in the sink plumbing can look like a dishwasher problem.

Clean the Filter and Sump

On most modern dishwashers, the first place to look is the filter and sump at the bottom of the tub. The filter catches food particles, and over time it can become clogged with grease and debris that slows drainage and leaves a film on dishes. Many units have a two-part filter that twists out; consult your model's manual for the exact removal method.

Rinse the filter under warm running water and scrub it with a soft brush and a little dish soap. Remove any debris from the sump area around it, and check the sump cover for buildup. Cleaning this area monthly prevents most slow-drain complaints and also cuts down on odors. If your kitchen sink has a smell of its own, our article on kitchen sink odors covers the related drain issues.

Check the Drain Hose for Kinks and Clogs

Next, inspect the drain hose. With the power off, pull the dishwasher partway out or access it through the adjacent cabinet. Look for sharp bends, pinched sections, or a hose that has slipped and is crushed against the cabinet. Even a partial kink can stop water from moving.

If the hose looks clear, disconnect it at the disposal or sink end and empty it into a bucket. Grease and food sludge can coat the inside of the hose until it closes off. Flushing the hose with warm water can clear a soft clog. If the hose is brittle or hard, replacement is inexpensive and makes more sense than trying to clean it.

Garbage Disposal Knockout Plug and Clogs

If the dishwasher was recently installed and has never drained, check the garbage disposal. New disposals ship with a plastic knockout plug in the dishwasher inlet, and it must be removed before the dishwasher is connected. If it is left in place, the dishwasher has nowhere to drain. This is one of the most common installation oversights.

On a disposal that has been in use, food buildup can clog the inlet where the dishwasher hose connects. Run the disposal with plenty of water before starting the dishwasher, and clear any standing food waste. For noisy or sluggish disposals, see our guide to garbage disposal troubleshooting.

Clear the Air Gap and Sink Drain

If your dishwasher drains through an air gap mounted on the sink deck, that small fitting can clog with debris. Remove the decorative cover, lift out the inner cap, and clean the chamber and the small holes. A clogged air gap lets water back up into the dishwasher even when the pump is working.

If the dishwasher discharges into the sink drain or disposal, confirm that the sink itself drains freely. A clogged P-trap or a blocked sink drain will back water up into the dishwasher. Clearing the sink drain may solve the dishwasher problem entirely. Our guide to unclogging a drain covers safe methods for the trap and branch line.

Test the Drain Pump and Check Valve

If the filter, hose, air gap, and sink drain are all clear, the problem may be inside the unit. Start a cycle and listen near the bottom of the dishwasher during the drain portion. You should hear the drain pump running. If the pump hums but no water moves, something is still blocking the impeller or the pump may have failed. If there is no sound at all, the pump may not be getting power, or it may have burned out.

A stuck or worn check valve, a small flapper near the pump, can also prevent drainage or allow water to flow back in. Replacing a drain pump or check valve requires accessing the bottom of the unit, disconnecting wiring and hoses, and often tipping the dishwasher. Many homeowners reach this point and prefer to have a professional take over.

Preventing Future Drain Problems

A few habits keep a dishwasher draining freely:

• Scrape plates into the trash before loading, especially greasy foods and starchy items like rice and pasta.
• Never pour grease or cooking oil down the sink or into the dishwasher.
• Run hot water at the sink for a few seconds before starting the dishwasher so the drain is warm.
• Run the garbage disposal before starting a cycle if the dishwasher shares the disposal drain.
• Clean the dishwasher filter monthly and run a dishwasher cleaner or a vinegar cycle every few months.

When to Call a Professional

Call a plumber or appliance technician when:

• Water still will not drain after you have cleaned the filter, hose, air gap, and sink drain.
• The drain pump is silent or hums without moving water.
• You find standing water in the cabinet, under the sink, or around the base of the unit, which can indicate a leak.
• The sink and dishwasher both back up at the same time, which points to a blockage in the shared drain line.
• You are not comfortable working around the appliance's wiring and water connections.

Repeated backups in the shared kitchen drain line can also be a sign of a larger blockage farther down the pipe. If slow drains affect more than one fixture, it is worth having the line inspected rather than repeatedly clearing the same spot.

Getting Your Kitchen Back to Normal

Most dishwasher drainage problems come down to a clog in the filter, hose, disposal connection, or sink drain, and all of those are within reach of a careful do-it-yourselfer. Work through them in order, and you will usually find the culprit without touching the pump.

If the problem turns out to be the pump, the shared drain line, or a leak you cannot locate, GoPlumberz connects homeowners with licensed plumbing professionals who can diagnose and repair it. Call (888)239-9523 or visit our services page to get help in your area.