The short answer
Standing water in the bottom of a Cosmo dishwasher is almost always in the path between the filter and the disposer, not in the pump. This machine has a manual filter and a drain hose that goes to a disposer or an air gap, and the two most common causes are a blocked filter and a disposer knockout plug that was never removed at installation. Both are owner-fixable.
What you are actually seeing
- Water stands in the tub floor at the end of every cycle — Means: on-page
- The machine drains partly and leaves a shallow pool — Means: on-page
- Dirty water appears in the tub after the sink has been used — Means: on-page
- A gurgling from the sink whenever the machine drains — Means: on-page
- Water backs up into the sink when the machine drains — Means: on-page
- The cycle stops early with a full tub and a code — Means: different-fault — Go to: cosmo-dishwasher-cycle-fault
- Water on the floor rather than in the tub — Means: different-fault — Go to: cosmo-dishwasher-water-leak
- Body: Match what you see before you take anything apart. Water stands in the tub floor at the end of every cycle. The machine drains partly and leaves a shallow pool. Dirty water appears in the tub after the sink has been used. A gurgling from the sink whenever the machine drains. Water backs up into the sink when the machine drains. Some near-miss symptoms belong on a different page: The cycle stops early with a full tub and a code points at a cycle or control fault, covered on cosmo-dishwasher-cycle-fault; Water on the floor rather than in the tub points at a leak, covered on cosmo-dishwasher-water-leak.
Causes, ranked for this machine
- A blocked filter holding debris across the drain path — Why this rank: First because this machine has a manual filter with no disposer of its own, so everything that comes off the plates stops there
- A disposer knockout plug never removed when the machine was installed — Why this rank: Classic installation fault: the machine has never drained properly since the day it was fitted, and the symptom is present from the first cycle
- A blocked air gap on the worktop, where one is fitted — Why this rank: Cheap to clear, invisible until you take the cap off, and it produces exactly this symptom
- A kinked or sagging drain hose, or a missing high loop — Why this rank: The loop is what prevents sink water flowing back into the tub, and it is easily dropped when the cabinet is worked on
- A blocked drain pump or a failed pump — Why this rank: Last because everything above it is free and because a genuinely failed pump is far rarer than a blocked path
- Body: Ranked for a built-in kitchen dishwasher with an electronic control, a manual filter and a drain hose running to a disposer or an air gap. Most likely: A blocked filter holding debris across the drain path. First because this machine has a manual filter with no disposer of its own, so everything that comes off the plates stops there. Next most likely: A disposer knockout plug never removed when the machine was installed. Classic installation fault: the machine has never drained properly since the day it was fitted, and the symptom is present from the first cycle. Third: A blocked air gap on the worktop, where one is fitted. Cheap to clear, invisible until you take the cap off, and it produces exactly this symptom. Fourth: A kinked or sagging drain hose, or a missing high loop. The loop is what prevents sink water flowing back into the tub, and it is easily dropped when the cabinet is worked on. Fifth: A blocked drain pump or a failed pump. Last because everything above it is free and because a genuinely failed pump is far rarer than a blocked path.
What to check, in order
- Remove and clean the filter, and look at what comes out of it
- Check whether the machine has ever drained properly since installation
- Remove the air gap cap on the worktop and clear it
- Trace the drain hose under the sink for a kink, a sag or a missing high loop
- Body: Each check rules out the causes above it. First, remove and clean the filter, and look at what comes out of it. Second, check whether the machine has ever drained properly since installation. Third, remove the air gap cap on the worktop and clear it. Fourth, trace the drain hose under the sink for a kink, a sag or a missing high loop.
Checks you can safely make yourself
- Switch off at the breaker, bail the standing water out with a cup and a sponge, then twist out the filter and rinse it under a hot tap — Tools: cup, sponge, brush — Time estimate: half an hour
- Look into the sump under the filter with a torch and remove any glass, labels, seeds or bone fragments by hand — Tools: torch, gloves — Time estimate: a quarter of an hour
- If the drain hose goes to a disposer, run the disposer for a moment and check that the machine has ever drained properly since it was fitted — Tools: none — Time estimate: a few minutes
- Lift the cap off the air gap on the worktop, remove the cover and clear any debris from the chamber — Tools: none — Time estimate: a quarter of an hour
- Open the cabinet and lift the drain hose so it rises above the machine before it drops, securing it so it cannot sag again — Tools: cable tie, torch — Time estimate: a quarter of an hour
- Body: Checks an owner can make with the machine switched off at the breaker, or by watching a cycle. Step one: Switch off at the breaker, bail the standing water out with a cup and a sponge, then twist out the filter and rinse it under a hot tap. Tools: cup, sponge, brush. Time: half an hour. Step two: Look into the sump under the filter with a torch and remove any glass, labels, seeds or bone fragments by hand. Tools: torch, gloves. Time: a quarter of an hour. Step three: If the drain hose goes to a disposer, run the disposer for a moment and check that the machine has ever drained properly since it was fitted. Tools: none. Time: a few minutes. Step four: Lift the cap off the air gap on the worktop, remove the cover and clear any debris from the chamber. Tools: none. Time: a quarter of an hour. Step five: Open the cabinet and lift the drain hose so it rises above the machine before it drops, securing it so it cannot sag again. Tools: cable tie, torch. Time: a quarter of an hour.
Safety first
Safety
Switch off at the breaker before bailing the tub or reaching into the sump, and wear gloves: broken glass in the sump is the most common injury on this job. Never run the disposer with a hand near it. Unplug the appliance or switch off its breaker before removing any panel. A capacitor can hold a charge after the power is off. unplug-before-service
Where the owner fix ends
Call a technician when the filter and sump are clean, the disposer connection is proven open, the air gap is clear and the drain hose loops high, and the tub still holds water. That leaves the drain pump and the check valve, which need the machine pulled out and the lower panel off.
Nearest pages of the same kind
Generalized information
This page is generalized across the Cosmo dishwasher line. Front-control and top-control machines, and panel-ready and stainless fronts, share the ranking above but not every part, and this page does not cover a specific model or control revision. Family- and model-specific pages, where they exist, are linked below.
Links: - [Common COSMO Dishwasher Problems](/blog/cosmo-dishwasher-problems) - [COSMO Dishwasher: Abnormal Noise or Vibration](/blog/cosmo-dishwasher-abnormal-noise) - [COSMO Dishwasher: Does Not Clean or Dry](/blog/cosmo-dishwasher-cleaning-performance) - [COSMO Dishwasher: Controls, Display or Error Code](/blog/cosmo-dishwasher-control-fault)
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
