Won't drain on your Whirlpool DP8700XTN3
A dishwasher that won't drain is failing somewhere in a short chain from the sump to the house drain: the drain pump pushes water out of the tub, the drain hose carries it up and over a loop or through an air gap, and the water enters the house drain through either a dedicated standpipe or the inlet on a garbage disposal. Each point in that chain can clog — and the single most common cause isn't the pump. It's food debris accumulated in the sump filter at the bottom of the tub. On brand-new installations, a specific failure mode dominates: the garbage disposal inlet has a factory 'knockout plug' that the installer has to remove before connecting the dishwasher. If that plug was forgotten, no water can pass regardless of how healthy the dishwasher's pump is. Check the sump filter first on an existing install, and check the disposal knockout on a new install, before assuming a component has failed.
Safety reminders
- Kill the breaker before opening any panel: Dishwashers are typically hardwired to a dedicated 120V circuit rather than plugged into an outlet, so there's no plug to pull. Always turn off the dishwasher's breaker at the panel before removing the kick plate, accessing the drain pump, or working inside the tub. Verify power is off with a non-contact voltage tester before reaching in.
- Sharp debris in the sump and filter: Broken glass, toothpicks, fruit stickers with backing staples, and small bones or shells collect in the sump and filter. Always inspect visually before reaching in, and pull debris out with tweezers or a disposable tool — not bare fingers. A small shard of glass in the sump is easy to miss and easy to cut skin on.
- Standing dishwasher water is not clean: Water trapped by a failed drain cycle carries detergent residue, food particles, and the slippery proteins and fats from whatever was rinsed off dishes. It can irritate skin and eyes, and it smells bad if left sitting for more than a day. Wear gloves when bailing water from the tub or cleaning the sump.
- Don't force additional cycles with water in the tub: Running another cycle on top of standing water risks overflow onto the floor and through the door gasket. Cancel the current cycle, bail water out of the tub manually with a cup or sponge, and diagnose the drain path before starting any new cycle. The door gasket is not watertight against significant volume.
How to approach this
Start inside the tub. Pull the lower rack out and locate the sump filter at the bottom — a cylindrical or flat-disk assembly in the center-rear on most models. On manual-clean filters, twist counterclockwise to remove and rinse under running water; on self-cleaning filter models, check the sump area around the drain for food debris anyway, since even self-cleaning filters miss larger items like broken glass or fruit stickers. Next, if the dishwasher connects to a garbage disposal, run the disposal briefly with water to clear any backed-up water, then confirm the disposal knockout plug was actually removed at installation — shine a flashlight into the disposal inlet (dishwasher connection port) and look for an obstruction. If there's an air gap on the countertop, twist off the cap and check for food debris clogging the device. Finally, pull the lower kick plate and inspect the drain hose for kinks, and if nothing else has been found, test the drain pump by listening for its motor during a drain cycle — a hum without water movement points at a jammed impeller, silence points at a failed motor or missing control signal.
Common causes
Ordered by how frequently each component is involved, based on service manual analysis.
Clogged sump filter or sump area
Most commonFood debris that doesn't fully dissolve in the wash collects in the sump at the bottom of the tub — especially fruit stickers, rice grains, popcorn kernels, and fat-stuck residue. On models with manual-clean filters, users often don't know to rinse them monthly. On self-cleaning filter models, larger debris like broken glass still accumulates in the sump around the filter housing. Pull the bottom rack and inspect with the tub empty.
Garbage disposal knockout plug still installed (new installs)
CommonWhen a dishwasher connects to a garbage disposal, the disposal's dishwasher inlet port ships from the factory with a 'knockout plug' that must be driven out with a hammer and punch during installation. If an installer skipped this step, no water can pass from the dishwasher into the disposal — the dishwasher fills and then can't drain. This is the dominant failure mode on brand-new dishwasher installs and appears within the first few cycles.
Clogged air gap (where installed)
CommonAn air gap is a small cylindrical device on the countertop or sink deck, required in California and some other jurisdictions and common throughout the western US. It prevents contaminated sink water from backflowing into the dishwasher. Food debris and detergent residue clog the air gap internals over years, slowing or stopping drainage. Twist off the decorative cap and clean the interior with a brush and vinegar — a frequently overlooked maintenance step.
Kinked or obstructed drain hose
CommonThe drain hose runs from the dishwasher's drain pump outlet up and over a high loop (or to the air gap), then back down to the disposal or standpipe. Kinks can form when the dishwasher was pushed back into the cabinet during install, and the interior of the hose builds up grease and food residue over years. Disconnect both ends and run water through it to confirm clear flow.
Failed or jammed drain pump
CommonThe drain pump mounts below the sump and is driven by either a dedicated motor or a shared motor with the circulation pump. Foreign objects (broken glass shards, fruit stickers, small bones, pits) can jam the impeller — a hum with no water movement is the classic signature. True motor failure (open windings, bad bearings) produces silence on drain command. Access the pump by removing the kick plate and lower service panel. Replacement pumps run $50-150.
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