The short answer
On the COSDWI family the usual reason a Cosmo dishwasher is leaving water in the bottom is disposer or shared branch blocked, and that is where the order below departs from the brand-generic article one level up: on the disposer-connected build it outranks filter and sump packed with debris. The check that confirms which build you have is simple — look under the sink: a drain hose entering the side of a food disposer means the machine drains through it. 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
- The tub empties and then refills — Siphoning back, which is the loop or the non-return valve.
- It started right after a new disposer was fitted — The knockout plug, until proven otherwise.
- The sink drains slowly as well — A shared blockage downstream, which is plumbing rather than appliance.
- Standing water in the sump at the end of every cycle — The defining symptom, and it says nothing yet about where the blockage is.
- Water with debris floating in it — A filter that has stopped holding anything back.
- 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 COSDWI family
- Disposer or shared branch blocked — Ranked first here: the machine shares its outlet with the sink, so a blockage downstream presents as a dishwasher fault while the sink drains slowly as well.
- Filter and sump packed with debris — Second: 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.
- Non-return valve stuck — Third: the valve that stops waste returning can stick open or shut. Shut, nothing leaves; open, everything that left comes back.
- Air gap or a disposer knockout still in place — Fourth: the air gap on the worktop is a small chamber that silts up, and a newly fitted disposer that still has its knockout plug gives the water nowhere at all to go.
- 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.
- Drain hose kinked behind the machine — Sixth: it dates the fault precisely: the machine drained yesterday and does not today, and nothing inside it changed.
Check in this order, and why
- Run the sink and see whether it drains freely — A slow sink and a wet dishwasher share one blockage.
- Lift the filter out and clear the sump by hand — The one that needs no tools.
- Note whether the tub refills after it has emptied — Water that returns points at the valve rather than the pump.
- Lift the air-gap cover on the worktop and clear it — A small chamber that silts up quietly and stops the flow completely.
Before you open anything
Safety
Power off at the spur, water off at the valve, then open anything. Those two come first because the wiring and the plumbing in this cabinet run alongside each other. Leave the door latch alone: defeating it lets a hot cycle run with the door open. Bail the water out before you tip the machine forward, and treat anything in the sump as sharp until you have seen it. Get a second person before you pull the cabinet out or tilt it.
Models in the COSDWI family
Reference| Model number | Family key |
|---|---|
| COS-DWI240TT*** | cosmo:dishwasher:cosdwi |
| COS-DWI24TTG | cosmo:dishwasher:cosdwi |
| COS-DWI24TTR | cosmo:dishwasher:cosdwi |
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.
