Dishwasher Not Draining? 6 Causes and How to Fix Them
Standing water and a sour smell usually point to a clog you can clear in an afternoon
A dishwasher full of cloudy water at the end of a cycle is one of those problems that looks worse than it usually is. In most homes the cause is a blocked filter, a greasy drain hose, or a sink drain that is already half clogged — all of which are findable with a flashlight, a towel, and about an hour.
What you should not do is keep running cycles hoping the water will clear. Standing water strains the drain pump, invites mold into the tub, and can leak under the cabinet onto flooring. Work through the checks below in order, cheapest and simplest first, and you will usually find the blockage before you reach the pump.
Start With Four Quick Checks
Before pulling the appliance out, rule out the obvious. These four checks solve a surprising share of "dishwasher won't drain" calls.
Look at the sink. Fill the kitchen sink and let it drain. If the sink drains slowly or gurgles, you have a shared drain clog, and the dishwasher is simply backing up into a restricted line.
Run the disposal. With water running, run the disposal for 15 seconds. Food paste in the disposal throat blocks the dishwasher's drain path more often than any other single cause.
Check the air gap. If you have a small chrome cylinder on the sink deck next to the faucet, pull its cap and clear any debris. A blocked air gap stops drainage completely.
Confirm the cycle finished. A pause or cancel mid-cycle, a power blip, or a door opened late can leave water in the tub with nothing wrong at all. Run a rinse-and-hold cycle and watch whether it pumps out.
The Six Causes Behind a Dishwasher That Won't Drain
Once the quick checks are done, the problem is almost always one of these six. The order matters: work from the tub outward toward the house drain.
1. Clogged filter and sump screen. Food particles, broken glass, and labels collect in the bottom of the tub. When the screen clogs, water cannot reach the pump intake. This is the most common cause by a wide margin.
2. Greasy or kinked drain hose. The corrugated hose behind the unit traps grease and grit, and a hose that was pushed back too far during installation can fold and pinch shut.
3. Blocked air gap or disposal port. The path from the dishwasher into the sink plumbing is narrow. Grease and food paste close it easily, and a new disposal installed without removing its knockout plug blocks it permanently.
4. Clogged kitchen drain line. If the sink drains slowly too, the blockage is downstream in the branch drain or trap arm, not in the appliance.
5. Stuck check valve. Many dishwashers have a small flapper or ball valve at the pump outlet that keeps dirty water from flowing back. Debris jams it open or shut.
6. Failed drain pump or impeller. If the pump hums without moving water, or is silent when it should run, the impeller may be jammed by glass or the motor may have failed.
Step-by-Step: Clearing the Drain Safely
Turn off the breaker that feeds the dishwasher and shut off the water supply valve under the sink before you touch anything inside the tub. Water and electricity in the same cabinet is not a combination to gamble with.
Remove the standing water. Use a cup, a turkey baster, and towels. Soaking it up with a wet/dry vacuum is faster if you have one.
Clean the filter assembly. Twist out the cylindrical filter and lift the flat screen beneath it. Rinse both in the sink with dish soap and a soft brush, then check the sump cavity for glass or bones with a flashlight.
Clear the air gap. Pull the chrome cap, lift out the inner body, and rinse it. Reassemble and test before moving on.
Inspect the drain hose. Pull the unit forward enough to see the hose. Look for kinks, then disconnect it at the sink end over a bucket and check for grease buildup. If the hose is coated inside, replace it rather than trying to rinse it clean.
Check the disposal connection. If the hose enters a disposal, confirm the knockout plug was removed at install. On a new disposal this is the single most common mistake.
Test the pump. With the unit powered and the tub partly filled, start a drain cycle and listen. A healthy pump gives a steady hum and water disappears within a minute. Humming with no movement means a jammed impeller; silence means an electrical or motor fault.
Clear the house drain if needed. If the sink and dishwasher both back up, the branch drain needs snaking. That is plumbing work, not appliance repair.
Water Won't Leave the Kitchen Sink Either?
Call now to speak with a local plumber about clearing the kitchen drain line behind your dishwasher.
Almost every dishwasher drain clog starts with what goes into the machine or down the sink. These habits make the biggest difference.
Scrape, don't rinse. Knock solids into the trash. Rinsing sends grease and paste straight into the drain path, where it cools and sticks.
Never pour grease down the sink. Pour it into a can, let it set, and throw it away. Hot water only moves grease a few feet down the pipe.
Run hot water at the sink first. Turn on hot water for 20 seconds before starting the dishwasher so the shared drain line is warm and flowing.
Clean the filter monthly. It takes two minutes and prevents most sump blockages.
Use the right detergent. Pods in a short cycle, or too much powder in soft water, leave residue that thickens drain lines over time.
Keep the hose looped high. The drain hose should rise before it connects to the sink plumbing. A low, sagging hose siphons dirty water back into the tub.
Run a monthly hot rinse. A cup of white vinegar in an empty hot cycle helps dissolve film before it hardens.
One more preventive note: if you are replacing a garbage disposal, follow the instructions about the knockout plug. A surprising number of "dishwasher won't drain" service calls end with a plug still sitting in the disposal port.
Frequently Asked Questions
Why is there standing water in my dishwasher after a cycle?
A little water in the sump is normal. An inch or more across the tub usually means a clogged filter or screen, a blocked air gap or drain hose, a restricted sink drain, or a failing drain pump.
Can a clogged garbage disposal stop a dishwasher from draining?
Yes. Most dishwashers drain through the disposal or sink tailpiece. If that path is blocked — or the knockout plug was never removed after a new disposal install — water has nowhere to go.
Is it safe to keep using a dishwasher that won't drain?
No. Stop running cycles. Standing water strains the pump, causes odors, and can leak under the cabinet. Clear the blockage first.
Reviewed by: First Plumbing Pro Editorial Team — Checked against manufacturer drain-path guidance and standard kitchen plumbing practice.
When to Call a Professional Plumber
Filter cleaning, air gap clearing, and hose inspection are reasonable DIY jobs. Call a plumber when the problem stops being about the appliance and starts being about the pipes.
The kitchen sink drains slowly or backs up when the dishwasher runs.
Water pools under the cabinet, on the floor, or in the basement below the kitchen.
You smell sewer gas or see repeated backups at the sink and dishwasher together.
The drain hose is clear but water still will not leave the tub — the branch drain or trap needs proper snaking.
You have already cleared the filter twice and the clog keeps returning within weeks.
The pump hums but nothing moves, and you are not comfortable testing the appliance electrically.
A kitchen branch drain that clogs repeatedly is usually telling you something about the condition of the pipe, not the dishwasher. If your sink and dishwasher are backing up together, call (888) 239-9523 to have the line inspected and cleared properly.