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

Dishwashers are a lifesaver when it comes to tackling post-meal cleanup. During a wash cycle, water is pumped in to remove food, grease, fat, and other stubborn debris from your dishes. Before the cycle ends, the dishwasher drains out the soap, water, and any small bits of food that can pass through the filter. But if you open your dishwasher after the cycle and find it full or partially filled with water, you might be asking yourself, "Why isn’t my dishwasher draining?"

Here are seven possible reasons why your dishwasher might be backing up, along with ways to fix the problem.

Types of Dishwasher Drain Connections

Before you begin troubleshooting, it's important to understand the different types of dishwasher drain connections to identify which one your appliance uses. The four common configurations are high loop to disposal, high loop to drain, air gap to disposal, and air gap to drain.

• High loop to disposal: This setup involves a drain hose looped to the top of the cabinet, then connected to the garbage disposal. The high loop is usually secured with tape, string, or a chain to prevent water from flowing back into the dishwasher.

• High loop to drain: Similar to the first setup, but the hose connects to the drain line instead. The connection should be above the P-trap to prevent sewer gases from entering the dishwasher.

• Air gap to disposal: This involves a drain hose running up to a small, cylindrical knob (the air gap) on the back of the sink, then to the garbage disposal. The air gap prevents dirty sink water from siphoning back into the dishwasher.

• Air gap to drain: Here, the hose runs from the air gap knob to the drain line. The connection on the drain line should be above the P-trap to prevent sewer gases from escaping into the dishwasher, while the air gap stops dirty sink water from backing up into the dishwasher.

Common Causes of a Dishwasher Not Draining Properly

1. Clogged Garbage Disposal

If your kitchen has a garbage disposal, it could be why your dishwasher isn’t draining. When food and debris clog the garbage disposal, it leaves less space for the dishwasher’s wastewater to drain. Turn on the disposal and run cold water to clear the blockage.

If that doesn’t work, you may need to unclog it manually. Turn off the disposal and unplug it, or shut off the breaker. Use a flashlight and long-handled tongs or pliers to remove the blockage. Alternatively, pour 1/4 cup of baking soda and 1/2 cup of white vinegar into the disposal. Allow the mixture to sit for 5-10 minutes before rinsing with cold water.

2. Obstructed Air Gap

If you have an air gap to disposal or air gap to drain setup, the drainage issue might be due to an obstructed air gap. Located on the back edge of the sink, the air gap prevents vacuums from forming in the drainage system, stopping drain water from being siphoned back into the dishwasher.

If the air gap is clogged, remove the cap and clean inside. Disconnect the drain hose and inspect it for clogs. Clear the hose, reconnect it, and see if the problem is resolved.

3. Out-of-Position High Loop

A high loop system uses gravity to stop wastewater from draining back into the dishwasher. If the drain hose shifts or is knocked out of position, it can cause backing up. Return the hose to its proper high loop position at the top of the counter to fix the issue.

4. Incorrect Dishwasher Detergent

It’s important to use dishwasher-specific detergent. Using regular dish soap or laundry detergent can create clogs in the dishwasher. Scoop out any remaining soap and water from the bottom of the appliance. Once mostly clear, run a normal cycle with the correct detergent.

To remove leftover dish soap, pour 1/4 cup of vegetable oil into the bottom of your dishwasher and run a Quick Wash cycle without any detergent.

There's a notable difference between dish soap and dishwasher detergent: the former relies on suds to clean, while the latter uses enzymes to break down proteins and starches.

5. Drain-Basket Food Buildup

If the drain hose, air gap, and disposal are clear, the blockage might be in the drain basket at the base of the dishwasher. This part usually looks like an upside-down basket attached by screws or snap fasteners.

Remove the cover, loosen any fasteners, and pull the drain basket out. Empty its contents into the garbage, rinse any remaining debris, clean the basket, and reinstall it. Add the correct detergent and run a normal cycle to see if the issue is resolved.

6. Kinked Drain Hose

The drain hose might become kinked or crimped if a heavy object is shoved under the sink. This impedes water flow, so manually straighten the hose. If it kinks again, consider replacing it as it’s more likely to kink in the same spot.

7. Blocked Drain Hose

Similar to a kinked hose, a blocked or clogged drain hose will prevent proper draining. Disconnect the hose from the garbage disposal or drain line to inspect for obstructions. If the clog isn't visible, you may need to access the other end by removing the lower front panel of the dishwasher.

Use a flashlight to check the hose for clogs. If the blockage is near an end, carefully remove it with a thin screwdriver or wire. If it’s in the center, you might need to replace the entire hose, as they can't handle the twisting and cutting motion of a plumber's snake without getting damaged.

When to Call a Professional

While many dishwasher drainage problems can be fixed by an experienced DIYer, if you’ve tried the above solutions and your dishwasher still isn’t draining, it's time to call a professional.

Problems may involve faulty parts like drain pumps, drain motors, pump pistons, nut assemblies, or the check valve. A trained plumber or appliance repair technician can identify the issue and get the necessary parts to fix it.

More Appliance Repair Guides

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