Dishwasher Won't Drain: Every Cause, in Order

Last updated: October 2026

You open the dishwasher and the dishes are clean-ish, but the bottom of the tub is a swamp. Before anything else, one calibration: a thin film of water sitting in the sump — the recessed area under the filter — is normal. The sump never fully empties. What is not normal is deep standing water you can scoop out with a cup. If that's what you have, work this list from the top. It's ordered the way a technician works it: free and common first, parts and money last.

Step 1: Was a garbage disposal just installed?

If the draining problem started right after a new garbage disposal went in, stop here — you've almost certainly found it. A new disposal's dishwasher inlet port is sealed with a plastic knockout plug, and the installer is supposed to punch it out before connecting the dishwasher hose. When they forget, the dishwasher tries to drain into a sealed pipe. Bosch's own service documentation for its drain error code lists removing this plug as a fix, which tells you how often it happens.

With the disposal switched off, shine a flashlight into it and look for a loose plastic disc sitting in the chamber — that's the plug, already knocked out but never fished out. Or disconnect the dishwasher hose at the disposal inlet (disposal unplugged) and check whether the plug is still seated in the nipple. Either way: plug out, hose back on, run Cancel/Drain, and the swamp should clear. Cost: $0. This is also the single most expensive miss in dishwasher repair — people have paid for pumps and even control boards over a ten-cent piece of plastic.

Step 2: Clean the filter — really clean it

Pull out the bottom rack and remove the filter assembly at the bottom of the tub (on most models it twists or lifts out). Rinse it under the tap and scrub off the greasy film. A clogged filter restricts the water leaving the tub, and it's so central to drain problems that Bosch gives it its own error code (E22, filter blocked) and Samsung flags a clogged filter as 1E. While the filter is out, look down into the sump for debris — labels, seeds, fragments of glass.

Step 3: Do the listen test

This one observation splits the whole diagnosis in two. Press Cancel/Drain (or start a cycle and listen at the drain stage) and put your ear near the bottom of the machine:

• It hums or buzzes: the pump is getting power and trying. The pump is probably alive — something is blocking the water's path, or something hard is jammed in the pump's impeller. Go to step 4.
• It grinds or rattles: something is in the pump — classically a chip of glass, a fruit pit, or a bone fragment. Go to step 4.
• Total silence: the pump isn't running at all. Skip to step 5.

Step 4: Work the drain path (pump is trying)

Work outward from the tub, in this order:

1. The pump impeller. On many Bosch models there's a small cover over the drain pump in the sump. Power off, pop the cover, and clear whatever is jamming the impeller — then confirm the impeller spins freely and reseat the cover firmly. A loose or missing cover is itself a Bosch fault (E25), because it lets debris straight back into the pump.
2. The air gap. If your sink has a countertop air gap (a small chrome cylinder next to the faucet), pop its cover off and clean out the cap and inner tube. Air gaps clog quietly and stop drainage completely.
3. The hose. Check behind and under the machine for a kinked or crushed drain hose. Confirm the hose loops up to countertop height (a "high loop") before dropping to the disposal or drain — that loop matters for proper draining.
4. The sink side. Run the disposal to clear its chamber, and check that the sink itself drains freely. A backed-up house drain presents as a dishwasher drain problem.

Step 5: The silent pump — test before you buy

If the pump never makes a sound, either the pump motor has failed or the control board isn't sending it power. A two-minute test separates those two very different bills. Breaker off, access the drain pump (usually behind the lower toe-kick panel), unplug its connector, and measure resistance across the pump's terminals. Most dishwasher drain pumps read roughly 15–40 ohms; Bosch pumps typically read higher, so check your model's spec. A reading of OL (open) or 0 ohms means the pump is dead — it's a $30–100 part, reasonable DIY for the handy, or a $150–350 pro replacement. A pump that reads in range but never runs points at the control board, which is a $250–600 installed repair and technician territory.

When it's time for a tech — and when it's time for a new dishwasher

Call a technician if the drain path is clear, the pump tests good, and it still won't drain (board territory); if you find an error code pointing at the control; or if water is appearing under the machine (a drain problem plus a leak is a different job — see our guide to a dishwasher leaking from the bottom). Typical professional repairs run $160–300; a drain pump replacement $150–350. And do the age math: dishwashers live about 9–12 years, and a repair quote over half the price of a new machine ($500–1,000, plus $150–300 to install) on an older unit usually means replace. Brand-specific walkthroughs: Bosch E24 and Samsung 5C — and if yours hums but doesn't run, that sound has its own guide.