A dishwasher that will not drain is one of the most common appliance failures, and one of the most commonly misdiagnosed. The typical homeowner reaction is to call a plumber, but 90 percent of drain problems trace to issues the owner can fix in 30 minutes with a screwdriver and a bucket. This guide walks through the systematic diagnosis: starting at the cheapest test, escalating through the drain path, and arriving at a definitive answer. Most drain problems are at the filter, the hose, or the disposal connection. Only rarely is the drain pump itself at fault.
Step 1: confirm the symptom
A “dishwasher won’t drain” complaint usually means one of three things. The tub has standing water above the filter at the end of a cycle. The dishwasher displays a drain error code. Water leaks from the door bottom during the drain phase.
Each pattern points to a slightly different root cause. Standing water means the drain pump is not moving water out, or the water has nowhere to go. A drain error code means the pump is running but the dishwasher’s water level sensor still detects water above the threshold. A drain-phase leak means water is making it to the hose but escaping along the way.
Note which pattern you have before starting the diagnosis. It will narrow the search.
Step 2: clean the filter
This is the first check on every diagnosis. The filter sits at the bottom of the tub, under or adjacent to the lower spray arm. Most modern dishwashers have a two-piece filter: a fine mesh cup that twists counterclockwise to remove, and a coarse outer screen underneath.
Pull both filter parts out. Look at the underside of the fine mesh: a glaze of grease and food residue is normal. A complete coating that water cannot pass through is a clog.
Rinse both filter parts under hot tap water with an old toothbrush. Scrub the mesh thoroughly. Refit, making sure the filter seats fully and twists tight clockwise.
About 30 percent of “won’t drain” complaints resolve at the filter clean alone. The dishwasher’s drain pump will struggle if water cannot pass through the filter into the pump intake.
Step 3: check for visible obstructions in the sump
Pull out the filter again and shine a flashlight into the sump area underneath. The sump is a recessed cavity where the drain pump pulls water from. Common obstructions are pieces of broken glass, fruit pits, popcorn kernels, twist ties, broken plastic fragments, paper labels, and bone chips.
Wear gloves. Reach into the sump with your fingers and feel around for hard objects. Remove anything you find. If you cannot see clearly, use a wet-dry vacuum hose to suck out water and small debris.
About 20 percent of drain complaints have a foreign object in the sump that blocks the pump impeller intake.
Step 4: confirm the air gap or high loop
The dishwasher drain hose runs from the back of the dishwasher to the kitchen sink area. It must rise above the disposal or sink drain connection to prevent backflow. There are two ways to do this: an air gap (a small chrome fitting on the countertop, required by some local codes) or a high loop (the hose itself routed up under the countertop, secured with a zip tie or clip).
If you have an air gap, look at it. A clogged air gap shows water spilling out of the cap during a drain cycle. Pop off the chrome cap, lift out the inner plastic insert, and clean both with a paper towel and a small brush. Reassemble. Air gap clogs are common and 5 minutes to fix.
If you have a high loop, check that the hose actually rises to a high point. A high loop that has sagged below the disposal inlet creates a siphon condition that prevents drainage. Lift the hose up to its proper position and secure with a zip tie.
Step 5: test the disposal and disposal inlet
The dishwasher drain hose almost always connects to the side of the garbage disposal at a small barb fitting. If the disposal is clogged with food, the dishwasher cannot drain through it.
Run the disposal with cold water for 30 seconds. Listen for the normal grinding sound and watch the sink to confirm water drains freely through the disposal.
If the disposal is clogged, fix it first. The dishwasher will not drain properly until the disposal does.
Also check that the knockout plug inside the disposal’s dishwasher inlet was removed when the disposal was installed. The plug is a thin plastic disk that blocks the dishwasher port and must be punched out with a hammer and screwdriver before the dishwasher drain hose is connected. About 5 percent of “new disposal won’t drain” complaints trace to this issue.
Step 6: inspect the drain hose
The drain hose is the soft corrugated black or gray hose that runs from the back of the dishwasher up to the disposal or air gap. Disconnect the dishwasher (unplug from power and turn off water) before working on the hose.
Run your hand along the length of the hose feeling for kinks or hard lumps. A kink restricts flow. A hard lump usually means a food mass has accumulated inside.
Disconnect the hose at the dishwasher end. Hold it over a bucket and pour 1 gallon of warm water through it from the disposal end. The water should flow freely through to the bucket. If it does not, the hose has an internal clog.
To clear an internal clog, run a plumber’s snake through the hose, or replace the hose entirely. A universal drain hose costs $15 to $25 at any hardware store. Manufacturer-specific hoses run $35 to $60 but are not necessary for most dishwashers; the universal hose fits the standard barb fittings on both ends.
Step 7: check the drain pump
If the filter is clean, the sump is clear, the disposal works, and the hose flows freely, the problem is the drain pump itself.
The drain pump is located underneath the dishwasher tub and is accessed by either removing the bottom kickplate (most North American models) or laying the dishwasher on its back (most European models). The pump is a small motor with an inlet from the sump and an outlet to the drain hose.
Common drain pump failures are foreign objects jammed in the impeller (small bones, glass shards, plastic fragments), worn impeller blades, and motor failure.
Spin the impeller by hand. It should rotate freely with no grinding. If it does not spin or is rough, there is debris jammed in or the impeller is worn.
Drain pump replacement costs $40 to $120 for the part and 1 to 2 hours of work for a competent DIYer. If you are not comfortable with this level of disassembly, this is the point to call a service technician.
Step 8: rule out the wall drain or sink stack
In rare cases, the dishwasher drain is fine but the wall drain serving the kitchen sink is partially blocked. Symptom: water backs up into the sink whenever the dishwasher drains.
Test by running the dishwasher with the sink open and watching whether the sink drains freely. If water rises in the sink during the drain phase, the wall stack is restricted and a plumber is needed.
Cost expectations
Filter clean, sump cleanout, air gap or high loop fix, and disposal cleanout: 10 to 15 minutes each, no parts. Drain hose flush or replacement: 30 minutes, $15 to $25 for new hose. Drain pump replacement: 1 to 2 hours, $40 to $120 for the part. Wall stack plumber call: $200 to $400.
The vast majority of drain complaints resolve at steps 2 through 5 with no parts purchased. For smell-related drain issues, see our dishwasher smells causes and fixes guide. The methodology page covers our full appliance test framework.
Frequently asked questions
How much standing water is normal at the bottom of a dishwasher?+
A quarter to half a cup of water at the very bottom of the tub, right around the filter, is normal. It is residual rinse water that did not fully drain at cycle end and serves to keep the drain pump seals from drying out. More than half a cup, or water that rises above the filter housing, indicates a drain problem.
Why does my dishwasher only drain partially?+
Partial drain usually means a partial clog in the drain hose or a worn drain pump impeller. A fully clogged hose stops drain entirely; a partial clog slows it. Inspect the hose for soft spots, kinks, and obvious clogs. Run your hand along the length of the hose with the dishwasher running on drain mode; you should feel water moving freely through the hose.
Can I use Drano or chemical drain cleaner in a dishwasher?+
No. Caustic drain cleaners damage the rubber seals and gaskets in the dishwasher drain pump and hose. Use only mechanical methods (snake, hose flush, disposal cleanout) and mild cleaning agents like vinegar and baking soda. Chemical drain cleaners are also not effective on the typical dishwasher clog, which is grease and food residue, not the hair and soap mass that drain cleaners are formulated to dissolve.
Should I replace the drain hose or just clean it?+
Clean first, replace if cleaning fails or the hose shows visible damage. A new universal drain hose costs $15 to $25 and installs in 20 to 30 minutes. Manufacturer-specific hoses for Bosch, Miele, and KitchenAid run $35 to $60. Replace if the hose is over 10 years old, has cracked sheathing, or has a permanent kink that cannot be straightened.
Why did my dishwasher drain stop working right after I installed a new garbage disposal?+
The knockout plug. Every new disposal ships with a plastic knockout plug blocking the dishwasher drain inlet. The plug must be removed with a hammer and screwdriver before connecting the dishwasher drain hose. If the plug is still in place, the dishwasher pumps water against a sealed inlet and either backs up into the tub or leaks at the hose connection.
