Why a dishwasher stops draining
A dishwasher drains through a short, crowded path: from the sump under the filter, through the drain pump, past a check valve, up the drain hose to a high loop or an air gap, and into the disposal or the sink drain. Any of those points can hold water back. Food and glass collect in the filter and the sump; a pit or a shell jams the pump impeller; the check valve sticks and lets water fall back; a hose without a high loop lets sink water return; and a disposal installed with its knockout plug still in place blocks the outlet entirely. The pump motor and the control that runs it fail less often, usually after a surge.
Charleston kitchens bring their own patterns. Panel-front Bosch and Miele units South of Broad, in Ansonborough and across Daniel Island drain quietly, so the first sign is a smell or a wet toe-kick, and on heart-pine that matters. Oyster shell, shrimp shell and pistachio hulls jam more pumps here than anywhere we know. Summer storms send surges through control boards from Mount Pleasant to West Ashley. Rentals near the College and turnover houses in North Charleston run a load a day with little rinsing. The water is not the trouble: Charleston Water System and Mount Pleasant Waterworks are moderately soft, so scale is rare; what we find is debris, a stuck valve or a hose routed wrong.
The usual causes, most to least common
| Cause | What you notice | What we do |
|---|---|---|
| Filter and sump clogged with food and glass | Cloudy water left in the tub, a sour smell, dishes coming out gritty; often after a holiday load. | Clear the filter, sump and pump inlet, check the impeller for damage, and run a full cycle to a dry tub. |
| Disposal knockout plug never removed | The dishwasher has not drained since a new disposal went in, though it worked before. | Confirm the outlet is blocked, remove the plug through the disposal inlet, and test the drain path end to end. |
| Drain pump impeller jammed | A hum at the end of the cycle, then silence and standing water; sometimes a drain error on the display. | Open the pump, clear the shell or pit, check the impeller and the seal, and run a drain under load. |
| Check valve stuck | Drains, then some water comes back into the tub; a small puddle every morning. | Clean or replace the check valve at the pump outlet, and confirm the tub stays dry between cycles. |
| Drain hose kinked or without a high loop | Slow drain, or sink water showing up in the dishwasher; common after a kitchen remodel. | Reroute the hose with a proper high loop under the counter, clear any kink, and test a full drain. |
| Air gap blocked | Water bubbling out of the chrome cap on the sink deck while the dishwasher drains. | Clear the air gap and the short hose to the disposal, and confirm the drain runs without backing up. |
| Drain pump motor or control board failed | No hum at all when the drain should run, everything else in the cycle normal; often after a storm. | Meter the pump windings and the board output, replace the failed part, and run a complete wash to a dry tub. |
Safe things to check before you call
- Run the garbage disposal for thirty seconds with the water on, then start a drain cycle.
- Lift out the filter in the tub floor, rinse it, and check the sump for glass or shell.
- Look under the sink for a drain hose that is kinked or lies flat with no loop.
- If there is a chrome air gap on the sink deck, lift the cap and clear it.
- Bail the standing water with a cup and a towel so the technician can see the sump.
- Note whether the dishwasher hums at the end of the cycle; that detail helps the diagnosis.
When to stop and call
Call when the filter is clean, the disposal has run, the hose has a loop and the tub still holds water, or when the pump hums and nothing moves. Call sooner if water is showing at the toe-kick or the cabinet beside the machine feels damp, because a slow leak under a panel-front unit finds heart-pine and cabinet bases before it finds you. Meanwhile, bail the tub, leave the door ajar so it airs, and wash by hand rather than rerunning cycles. Most dishwasher visits across the peninsula, Mount Pleasant, West Ashley and James Island are next day, with pumps and check valves for the common brands on the van.
Questions about this symptom
We just had a new garbage disposal installed and now the dishwasher will not drain. Related?
Almost certainly. New disposals ship with a plug in the dishwasher inlet, and if the installer did not knock it out, the dishwasher has nowhere to send its water. It is the first thing we check after a disposal change in any Charleston kitchen. The fix is quick, and the technician tests the whole drain path while there so nothing else is waiting.
Is standing water in the bottom of the dishwasher normal?
A small amount in the sump under the filter is normal on many machines and keeps the seals wet. An inch across the tub floor after the cycle ends is not, and neither is water that returns overnight. The second case usually means a check valve or a hose that has lost its loop; the first means a jam, a clog or a pump.
Do you work on panel-front dishwashers in downtown Charleston kitchens?
Yes, most weeks. Bosch, Miele, Thermador and KitchenAid panel-front units in South of Broad, Ansonborough and the French Quarter are routine, and on Daniel Island as well. The panel comes off, the pump and check valve are serviced, and the panel goes back flush with the cabinet run. The $99 diagnostic is inside the written number you approve.
Why does a dishwasher in Charleston jam so often?
Shell. Oyster and shrimp shell, crab, pistachio hulls and olive pits go down with the plates and stop at the pump impeller, where they hold it still until the motor hums and quits. A sink strainer and a quick scrape before loading stop most of it. When it happens anyway, clearing the pump is a same-visit repair from the van.
Is a dishwasher that will not drain an emergency?
Not usually, and we schedule it next day across Charleston and the areas within twenty minutes of Laurens Street. It becomes urgent when the water is escaping onto a wood floor or into a cabinet base, and we treat it that way. We work six days a week, so a Saturday call can get a Saturday window when the route allows.