The short answer
On the COSDWC family the usual reason a Cosmo dishwasher is leaving water in the bottom is drain hose not looped high enough, and that is where the order below departs from the brand-generic article one level up: it outranks drain hose kinked behind the machine. The filter, the hose, the air gap and the disposer inlet are owner work; the pump under the sump is not.
What you observe on these models
- Water with debris floating in it — A filter that has stopped holding anything back.
- A hum at the end of the cycle with no water moving — A powered pump that cannot turn, which is a jam rather than a failure.
- Standing water in the sump at the end of every cycle — The defining symptom, and it says nothing yet about where the blockage is.
- It started right after a new disposer was fitted — The knockout plug, until proven otherwise.
- The tub empties and then refills — Siphoning back, which is the loop or the non-return valve.
- NEAR MISS — water on the floor rather than in the tub — That is a leak, and the leak page is the one to read instead.
Causes, most likely first on the COSDWC family
- Drain hose not looped high enough — Ranked first here: without a high loop, waste water siphons back into the tub and the machine appears never to have drained even when the pump ran perfectly.
- Drain hose kinked behind the machine — Second: it ranks high because it dates the fault precisely: the machine drained yesterday and does not today, and nothing inside it changed.
- Disposer or shared branch blocked — Third: the machine shares its outlet with the sink, so a blockage downstream presents as a dishwasher fault while the sink drains slowly as well.
- Non-return valve stuck — Fourth: the valve that stops waste returning can stick open or shut. Shut, nothing leaves; open, everything that left comes back.
- Drain pump impeller jammed — Fifth: glass, a fruit stone or a length of string around the impeller stops the pump dead or leaves it humming without moving water.
- Filter and sump packed with debris — Sixth: the pump can only move what reaches it. A filter matted with paper labels, seeds and fat leaves standing water in a machine whose pump is perfectly healthy.
Check in this order, and why
- Check the hose rises high before it falls to the waste — Without a loop, water siphons straight back into the tub.
- Pull the machine forward and follow the hose. Get a second person before you pull the cabinet out or tilt it. — A kink behind the cabinet stops drainage without anything being broken.
- Run the sink and see whether it drains freely — A slow sink and a wet dishwasher share one blockage.
- Note whether the tub refills after it has emptied — Water that returns points at the valve rather than the pump.
Before you open anything
Safety
Isolate the machine at the switched spur and close the supply valve before removing any panel. The door interlock must stay in circuit — it is what stops a hot wash spraying out at head height, and there is no safe reason to bypass it. Assume there is broken glass in the sump and use a cloth rather than your fingers. Dry the floor before working on an appliance whose wiring runs a hand's width from the water.
Models in the COSDWC family
Reference| Model number | Family key |
|---|---|
| COS-DWC24TTG | cosmo:dishwasher:cosdwc |
| COS-DWC24TTR | cosmo:dishwasher:cosdwc |
When to call a technician
Call when the filter, the sump, the hose, the air gap and the disposer inlet are all clear and the tub still holds water. At that point the pump is the remaining candidate, and it sits under the sump where the wiring and the water meet.
