The short answer
On the COSDWC family the usual reason a Cosmo dishwasher is leaving dishes dirty is spray arms blocked or not turning freely, and that is where the order below departs from the brand-generic article one level up: on the tall-tub build with a third level it outranks filter and sump carrying old debris. The check that confirms which build you have is simple — a shallow cutlery tray across the top of the cabinet means a third spray feed and a taller stack of water to lift. Arms, filter, dispenser, loading and programme are owner work; anything under the sump is not.
What you observe on these models
- 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.
- One shelf clean and the other dirty — A sector problem, which only a spray path can produce.
- Dishes clean but soaking wet at the end — A drying complaint rather than a cleaning one, and rinse aid is the first thing to check.
- 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 COSDWC family
- Spray arms blocked or not turning freely — Ranked first here: 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.
- Filter and sump carrying old debris — Second: the tell is a gritty film on everything rather than dirt in one place: a whole-load problem, evenly distributed, which points at the water rather than the spray.
- Incoming water not hot enough — Third: it ranks high because it is invisible from the control panel and because it explains the seasonal pattern owners often describe without being able to name it.
- Rinse aid empty — Fourth: it ranks on this list because the complaint is usually reported as a cleaning problem when it is really a drying one, and the two have completely different fixes.
- Detergent type, dose or a blocked dispenser flap — Fifth: a flap held shut by a tall item releases the detergent at the end of the cycle instead of the start, which reads exactly like a machine that has stopped cleaning.
- 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
- Spin each arm by hand and look through the jets — Seconds to do, and it is the only cause that produces one clean shelf and one dirty one.
- 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.
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 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.
