A dishwasher drains water from the tub through a pump, a hose, and — on most built-in installations — a connection to either your garbage disposal or a countertop air gap. When any link in that chain is blocked, water stays right where it is. Four causes account for the large majority of cases, and most of them are fixable in under half an hour with no tools beyond a screwdriver.
Sometimes it's not the dishwasher at all
If a nearby sink also drains slowly, the blockage may be in your home's plumbing rather than the appliance. It's worth running the sink faucet and checking for backup before assuming the dishwasher itself has failed.
The most common causes, in order of likelihood
1A dirty filter
This solves the problem more often than any other single step. The filter assembly sits at the bottom of the tub, usually accessible after removing the bottom rack. Twist it counterclockwise to unlock, pull it out, rinse it under warm water, and scrub away any food residue with a soft brush before reinstalling. Food particles and small debris restrict flow here constantly, especially if dishes aren't pre-rinsed before loading.
2A kinked or clogged drain hose
The hose that carries water from the dishwasher to the sink connection can develop a kink during installation, or get pushed against by items stored under the sink. Lint and soap residue can also build up inside it over time. Pull the dishwasher out slightly, check the hose's full length for bends, and confirm it has a proper high loop secured under the counter — without that loop, wastewater can actually flow backward into the dishwasher.
3A garbage disposal issue
Most built-in dishwashers drain through the garbage disposal. If the disposal itself is clogged or full, water has nowhere to go. Run the disposal with cold water for 30 seconds to clear it. There's also a commonly overlooked installation issue worth checking: every new disposal ships with a plastic knockout plug inside the dishwasher inlet, and it has to be physically knocked out with a screwdriver and hammer before water can flow through. If your dishwasher stopped draining right after a new disposal installation, this is very likely the cause — and it's a surprisingly common oversight even among professional installers.
4A blocked air gap
If your kitchen has one, the air gap is the small chrome or plastic cap mounted on the countertop near the faucet. It's there to prevent dirty water from siphoning back into the dishwasher, and its internal passages can clog with food debris and grease over time. If you notice water shooting out of the air gap during the drain cycle, that's the telltale sign it needs cleaning — remove the cap and clear it out with a small brush.
Filter's clean, hose is clear, disposal runs fine — still not draining?
The remaining causes are a failed drain pump, a stuck check valve, or an electrical control issue. Our technicians diagnose these on the same visit.
Call (814) 246-1412Less common causes worth knowing about
- A failed drain pump. If the pump motor has jammed — sometimes from a piece of broken glass or a stray utensil — or burned out entirely, you may hear a humming sound during the drain cycle with no water actually moving. This requires disassembly and isn't a typical DIY repair.
- A stuck check valve. This valve prevents drain water from flowing back into the tub. If it sticks closed, water can't leave even though the pump is working normally — less common, but worth ruling out if everything else checks out clean.
- An interrupted cycle. If the dishwasher's cycle was interrupted partway through, it can sometimes leave standing water without any actual component failure. Try resetting the dishwasher and running a fresh cycle before assuming something is broken.
When it's worth calling a technician
If you've cleaned the filter, checked the hose, run the disposal, and cleared the air gap but water is still standing in the tub, the cause is likely a failed pump, valve, or control issue — components that require proper diagnostic testing rather than guesswork. Continuing to run cycles on a dishwasher that isn't draining can also lead to odor and repeat problems, so it's worth addressing sooner rather than later.