Dishwasher Not Draining? Check These Five Things

Water sitting in the bottom of the dishwasher after a cycle means the drain path is blocked or the drain pump is not running. Start with the filter basket and the sump, then the drain hose where it meets the garbage disposal, then the air gap on the counter if you have one. If the dishwasher is new and has never drained once, go straight to the disposal knockout plug, because that is almost certainly your answer.

How much standing water is normal

A cup or less of clean water below the filter, down in the sump, is normal and intentional. It keeps the pump seal from drying out between uses. Water covering the floor of the tub, water above the heating element, or dirty water with food floating in it is a failed drain.

One case fools people. Clean water that appears after somebody uses the kitchen sink is sink water siphoning backward, which is a high loop or air gap problem covered below.

Start with the filter basket

Nearly every dishwasher built in the last fifteen years has a filter at the bottom center: a cylinder that twists out counterclockwise, inside a flat coarse screen that lifts out after it. Bosch, KitchenAid, Whirlpool, Samsung and LG all use a version of this.

Wash both pieces in hot water with dish soap and a soft brush. Here is the part manufacturers do not emphasize: water is hard across this metro, and grease plus dissolved minerals builds a waxy film on that fine mesh you cannot see or feel. A filter that looks clean can still be nearly closed, so soak it in white vinegar for 20 minutes.

With the filter out, put a flashlight in the sump. The regular offenders:

• Fruit stickers. Those labels are close to indestructible and pass straight through the mesh.
• Broken glass, especially a thin shard from a wine glass.
• Popcorn kernels, fruit pits and small bones.
• Chips off a plate rim.

Older machines, mostly pre-2010 Whirlpool and GE, use a hard food disposer instead of a filter. Nothing to clean there, but the chopper jams on bones and glass.

The knockout plug that strands brand new dishwashers

Most dishwashers here drain into the garbage disposal, and every new disposal ships with a molded plug sealing the dishwasher inlet, because plenty of installs never use it. The installer has to knock that plug out with a screwdriver and hammer and fish the slug out of the disposal body.

Skip that step and the dishwasher cannot drain a drop, on day one, forever. The tell is unmistakable: a new dishwasher, or one installed during a remodel, full of water after its first cycle, with a drain pump you can hear running normally. The pump is fine. It is pumping into a sealed wall.

Check it yourself. Shut off power to the disposal, put a bucket underneath, and pull the drain hose off the inlet. Solid plastic instead of an opening is your answer.

Drain hose, high loop, and air gap

The hose has to rise to the underside of the countertop and be strapped there before it drops to the disposal or standpipe. That rise is the high loop, and it keeps sink water from running back into the dishwasher. Missing high loops are common in older Kansas City kitchens where the dishwasher was added long after the house was built.

Then check the hose itself. It gets crushed when the machine is pushed back into its opening, especially during a remodel when new flooring made the space tighter. The corrugated section collects grease and scale, and it clogs most reliably in the last few inches where it necks down to fit the disposal inlet. That stretch is the most common clog point in the system.

The air gap is the small chrome cylinder on the counter beside the faucet. Not every kitchen has one, but plenty here do. When the line downstream clogs, water spills out of it during the drain, which is the clearest signal a dishwasher gives you. Twist off the chrome cover, lift the plastic cap underneath, and clear the body with a bottle brush.

One more check: fill the sink and let it out. If it drains slowly or gurgles, a clogged kitchen drain is backing up into the dishwasher, and that is a plumber's job.

The drain pump and a check valve stuck open

If the filter, hose and disposal inlet are clear, the pump is next. Modern dishwashers use a drain pump separate from the wash pump. Listen during the drain portion, which starts about a minute into any cycle.

• A hum with no water moving means a jammed impeller, usually on a glass shard or a fruit sticker.
• Silence means no power to the pump or an open winding.
• A loud rattling buzz means a damaged impeller.

Codes help. Bosch shows E24 for a blocked drain and E25 for a blocked drain pump, and LG shows OE. Many machines show no code and just blink a light the manual decodes.

The check valve is the part most people have never heard of. It is a small rubber flapper in the drain outlet that lets water out and not back in. Debris or hard water scale can hold it partly open, so water just pumped out slides back into the tub even though the pump ran perfectly. It is replaced with the pump or sump assembly.

Drain pump replacement sits inside our normal $150 to $400 range for parts and labor, with a one year warranty. See what else we handle under dishwasher repair and how we price it in our pricing section.

What to clear yourself, and what to leave alone

Do these yourself. Clean the filter and the sump. Clear the air gap. Check the hose for kinks and the disposal inlet for a knockout plug. Bail the standing water before we arrive.

Do not do these. Do not keep starting cycles hoping it clears, because running a drain pump against a blockage is how a jammed pump becomes a burned out pump. Do not pour chemical drain cleaner into a dishwasher, ever. Do not take the sump or pump apart unless you are ready to replace the gaskets.

Long term, hard water is what works against you. A cup of white vinegar through an empty hot cycle once a month keeps scale off the filter mesh, the check valve and the spray arms. The same applies to laundry, which we cover in our post on a washer that won't drain.

Call (816) 555-0123 when you want it handled. Call before noon and we can usually get there the same day with a two-hour window, and the $109 diagnostic fee is credited to the repair when you approve the written quote.