Why Is My Dishwasher Not Draining? 7 Common Causes of a Backup

Find out why a dishwasher might not be draining properly and how to fix it.

Updated on December 13, 2023

Dishwashers help make quick work of messy dishes after a big meal. Water is pumped into the appliance during a wash cycle to remove food, grease, fat, and other stuck-on debris. Before the cycle is complete, the dishwasher drains the soap, water, and any bits of food small enough to pass through the filter. But if you return after the cycle is complete and find it's still full or partially full of water, you'll probably wonder, "Why is my dishwasher not draining?"

These are seven possible reasons for a dishwasher backing up and ways to resolve the situation.

dishwasher in island in farmhouse kitchen — Emily Followill

Dishwasher Drain Connection Types

Before getting started with the troubleshooting process, it's necessary to have a basic understanding of dishwasher drain connection types so you can identify the type of connection your appliance has. The four common configurations include high loop to disposal, high loop to drain, air gap to disposal, and air gap to drain.

A high loop to disposal configuration has a drain hose that is looped up to the top of the cabinet and connects to the garbage disposal. This high loop is typically held in place with tape, string, or a chain, ensuring that water doesn't flow back into the dishwasher.
A high loop to drain setup has a drain hose that loops up to the top of the cabinet and connects to the drain line. The connection should be placed above the P-trap on the drain line to prevent sewer gases from entering the dishwasher.
An air gap to disposal configuration has a drain hose that runs to the top of the cabinet and connects to a small, cylindrical knob at the back of the sink before running to the disposal. The knob at the back of the sink is known as an air gap. The purpose of this air gap is to prevent dirty sink water from draining back into the dishwasher.
An air gap to drain setup has a drain hose that runs to an air gap knob at the back of the sink before running to the drain. The connection on the drain lines should be positioned above the P-trap to prevent sewer gases from exiting into the dishwasher, while the air gap prevents dirty sink water from flowing back into the dishwasher.

Common Causes of a Dishwasher Draining Improperly

1. Clogged Garbage Disposal

Not every kitchen has a garbage disposal, but if your configuration includes one, it may be the reason you're wondering, "Why is my dishwasher not draining?" When food and debris block a garbage disposal, there's less space for the wastewater from the dishwasher to drain. To resolve this problem, turn on the disposal and run cold water to help clear the blockage.

If the disposal remains clogged, you may have to dislodge the clog physically. Turn the disposal off and unplug it, or turn off the breaker to the appliance. Use a flashlight and a pair of long-handled tongs or pliers to identify and remove the obstruction. Alternatively, you can attempt to clear the clog by pouring 1/4 cup of baking soda into the disposal, followed by about 1/2 cup of white vinegar. Give the mixture five to 10 minutes to work, then rinse the disposal with cold water.

2. Obstructed Air Gap

For kitchens with an air gap to disposal or an air gap to drain configuration, the dishwasher drainage issue may result from an obstructed air gap. An air gap is a small, cylindrical knob positioned on the back edge of the kitchen sink. The purpose of an air gap is to prevent vacuums from forming in the drainage system, which in turn stops drain water from being siphoned back into the dishwasher.

If the air gap is clogged or obstructed, you'll need to clear the air gap by removing the cap to clean inside. Disconnecting the drain hose that runs to the air gap is also recommended so you can inspect it for any clogs. Clear the drain hose and reconnect it to the air gap, then check to see if this resolves the problem.

3. Out-of-Position High Loop

A dishwasher can back up if the drain hose shifts or gets knocked out of position in a high loop to disposal or high loop to drain kitchen configuration. A high loop system uses gravity to prevent wastewater from draining back into the dishwasher. Still, if the drain hose is not secured to the top of the counter, it may prevent water from properly draining out of the appliance. If this is the only problem with the dishwasher, the fix is relatively easy. Return the drain hose to the proper high loop position at the top of the counter to resolve the dishwasher drainage issue.

4. Incorrect Dishwasher Detergent

Typically, you should use dishwasher-specific detergent in your appliance. Using the wrong detergent or soap in the dishwasher can create a clog or blockage in the bottom of the appliance that prevents water from draining correctly. If you've used regular dishwashing liquid or laundry detergent instead of dishwashing detergent, you can usually resolve the problem by scooping out any remaining soap and water from the bottom of the dishwasher. When the bottom of the appliance is mostly clear of soap, water, and any other debris, run the dishwasher through a normal cycle with the correct detergent.

5. Drain-Basket Food Buildup

If the drain hose, air gap, and disposal all seem to be clear of obstructions, the blockage might be due to a buildup of food, fat, and other debris in the drain basket located at the base of the dishwasher. This part of the dishwasher typically looks like an upside-down basket that is attached by one or two screws or held in place with simple snap fasteners.

Remove the cover on the drain basket, loosen any fasteners, and pull the drain basket out of the dishwasher. Empty the contents of the basket into the garbage, then rinse out any remaining debris. Lightly clean the drain basket before reinstalling it in the base of the dishwasher. Add the appropriate detergent and start a normal wash cycle to determine if this resolved the issue.

6. Kinked Drain Hose

In some cases, the drain hose that leads from the dishwasher to the disposal or to the drain line may become kinked or crimped. This can happen if a large, heavy object is unceremoniously shoved under the sink without realizing that it's pushing against the drain hose. The kink in the line can fully or partially impede the movement of water through the hose, so you will need to manually straighten the hose to fix the dishwasher drainage issue. Also, it's important to note that once a drain hose kinks, it has an increased risk of kinking again in the same place. If this problem keeps occurring, it's recommended to replace the drain hose.

7. Blocked Drain Hose

Like a kinked drain hose, a blocked or clogged drain hose prevents a dishwasher from draining properly. Disconnect the hose inside the cabinet where it connects to the garbage disposal or drain line to inspect the hose for any food, grease, or other debris. If you can't spot a clog at that end of the hose, remove the lower front panel of the dishwasher to access the other end, where it connects to the dishwasher.

Place an old towel under the dishwasher, then disconnect the hose from the pump. Use the appliance manual provided by the manufacturer if you aren't sure what to look for or how your hose connects to the dishwasher. Once you've disconnected it, use a flashlight to look into the hose for any signs of blockage. If the clog is close to one end or the other, you can carefully remove it with a thin screwdriver or a piece of metal wire.

If the clog is in the center of the drain hose, you may need to replace the entire hose to resolve the issue. Drain hoses aren't designed to withstand the twisting and cutting motion of a plumber's snake. While a plumber's snake may be able to break up or remove the clog, there is a high chance that using a snake could cut, tear, or otherwise damage the dishwasher drain hose.

When to Call a Professional

There are various dishwasher drainage problems that an experienced DIYer can resolve on their own without needing to pay a professional plumber or dishwasher repair technician. However, if you've attempted the above fixes for a backed-up dishwasher and you're still asking, "Why is my dishwasher not draining?" it's recommended that you contact an appliance repair professional to resolve the problem.

Parts that may lead to drainage problems include faulty drain pumps, drain motors, drain pump piston and nut assembly, and the check valve. Trained plumbers and appliance repair technicians will be able to troubleshoot the situation, identify the problem, and source any necessary replacement parts to fix the issue.