The short answer
On the COSDWI family the usual reason a Cosmo dishwasher is leaving dishes dirty is filter and sump carrying old debris, and that is where the order below departs from the brand-generic article one level up: on the manual-filter build it outranks incoming water not hot enough. The check that confirms which build you have is simple — lift the lower basket and look at the sump: a removable cylinder and a flat mesh plate means the filter is yours to clean and nothing grinds debris for you. Arms, filter, dispenser, loading and programme are owner work; anything under the sump is not.
What you observe on these models
- One shelf clean and the other dirty — A sector problem, which only a spray path can produce.
- Food deposits redeposited on the upturned items — Debris coming back out of the sump, which is a filter story.
- Greasy film that wipes off with a finger — Heat rather than mechanics: fats need temperature to move at all.
- White cloudiness on glassware — Mineral film if it clears with a weak acid, etching if it does not.
- Gritty film on everything in the load — Evenly distributed, which points at the water being dirty rather than the spray being blocked.
- NEAR MISS — water standing in the sump at the end — That is a drainage fault, and the drainage page is the right one to read.
Causes, most likely first on the COSDWI family
- Filter and sump carrying old debris — Ranked first here: it ranks first on a machine with a manual filter because nothing grinds the debris for you, and because a filter that has never been cleaned is the single most common finding on these calls.
- Incoming water not hot enough — Second: detergent needs heat to work and fats need heat to move. A machine fed from a long cold run, or one whose cycle heats less to save energy, leaves greasy film on everything.
- Loading that shadows the spray — Third: it is worth naming plainly because it is the cause people are least willing to consider and the one that most reliably produces the pattern they are describing.
- Scale and hard-water film — Fourth: in a hard-water area the film is mineral rather than food, and no amount of extra detergent removes it. It builds slowly enough that the owner never notices a start date.
- Spray arms blocked or not turning freely — Fifth: this is the cause that produces the classic pattern of one clean shelf and one dirty one, which no detergent or temperature problem ever does.
- Weak circulation from the wash pump — Sixth: it sits low because everything above it is more common and free to exclude, and because this is the first cause on the list that is a real repair.
Check in this order, and why
- Lift out the filter and look at the sump beneath it — A loaded filter means the machine is washing with dirty water and redepositing it.
- Run the kitchen tap hot before starting a cycle — A free test that gives its answer on the very next load.
- Reload with nothing nested and no tray on the outer edge — Water travels in straight lines, so anything shadowing is simply not washed.
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 arms turn freely, the filter is clean, the water arrives hot, the load is sanely stacked and the result is still poor. At that point the question is whether the machine is developing pressure at all, and that is measured at the pump rather than guessed from outside.
