The short answer
A smell from a Cosmo dishwasher is nearly always biofilm in the places water sits between cycles: the filter, the sump, the gasket channel and the drain hose. On a machine with a manual filter this builds faster than owners expect, because nothing grinds the food that collects there. Cleaning it out is the whole fix.
What you are actually seeing
- A sour or stale smell when the door is opened — Means: on-page
- A drain or sewer smell rather than a sour one — Means: on-page
- Visible black or grey film around the filter or the gasket — Means: on-page
- Clean dishes that smell faintly of the machine — Means: on-page
- The smell is worst after the machine has stood unused for days — Means: on-page
- A burning or hot plastic smell — Means: different-fault — Go to: cosmo-dishwasher-electrical-safety
- Standing water in the tub with the smell — Means: different-fault — Go to: cosmo-dishwasher-drainage-failure
- Body: Match what you see before you take anything apart. A sour or stale smell when the door is opened. A drain or sewer smell rather than a sour one. Visible black or grey film around the filter or the gasket. Clean dishes that smell faintly of the machine. The smell is worst after the machine has stood unused for days. Some near-miss symptoms belong on a different page: A burning or hot plastic smell points at an electrical fault to stop using the machine over, covered on cosmo-dishwasher-electrical-safety; Standing water in the tub with the smell points at a drain fault feeding the smell, covered on cosmo-dishwasher-drainage-failure.
Causes, ranked for this machine
- A fouled filter and sump holding food debris between cycles — Why this rank: First because this machine has a manual filter with nothing to grind waste, so everything that comes off the plates sits there until it is removed
- Biofilm in the door gasket channel and around the door edge — Why this rank: The gasket channel stays wet and is almost never cleaned, which makes it the second reservoir
- A drain hose or air gap holding stale water — Why this rank: Explains a drain smell rather than a sour smell, and it is a different reservoir with a different fix
- Running only short, cool programmes so the machine never reaches a temperature that clears the film — Why this rank: A habit rather than a fault, and correcting it prevents the smell returning
- A dry trap or a plumbing smell coming from the sink rather than the machine — Why this rank: Last because it is not the appliance at all, but it is worth ruling out before any parts are considered
- 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 fouled filter and sump holding food debris between cycles. First because this machine has a manual filter with nothing to grind waste, so everything that comes off the plates sits there until it is removed. Next most likely: Biofilm in the door gasket channel and around the door edge. The gasket channel stays wet and is almost never cleaned, which makes it the second reservoir. Third: A drain hose or air gap holding stale water. Explains a drain smell rather than a sour smell, and it is a different reservoir with a different fix. Fourth: Running only short, cool programmes so the machine never reaches a temperature that clears the film. A habit rather than a fault, and correcting it prevents the smell returning. Fifth: A dry trap or a plumbing smell coming from the sink rather than the machine. Last because it is not the appliance at all, but it is worth ruling out before any parts are considered.
What to check, in order
- Remove and clean the filter and look at what comes out of it
- Wipe the gasket channel and the door edge and look at the cloth
- Run a hot maintenance cycle with a dishwasher cleaner and an empty machine
- Judge whether the smell is sour or drain-like, because the reservoir differs
- Body: Each check rules out the causes above it. First, remove and clean the filter and look at what comes out of it. Second, wipe the gasket channel and the door edge and look at the cloth. Third, run a hot maintenance cycle with a dishwasher cleaner and an empty machine. Fourth, judge whether the smell is sour or drain-like, because the reservoir differs.
Checks you can safely make yourself
- Switch off at the breaker, twist out the filter, wash it in hot water with a brush and clear the sump beneath it by hand — Tools: brush, gloves — Time estimate: half an hour
- Wipe the gasket channel and the door edge with a cloth and a mild detergent, working right into the fold — Tools: cloth, detergent — Time estimate: a quarter of an hour
- Run the hottest cycle with a proprietary dishwasher cleaner and nothing in the machine — Tools: dishwasher cleaner — Time estimate: one long cycle
- Lift the air gap cover on the worktop, where one is fitted, and clear any debris from the chamber — Tools: none — Time estimate: a quarter of an hour
- Run a hot programme rather than an eco or quick wash once a week for a month and judge whether the smell returns — Tools: none — Time estimate: a month of habit
- 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, twist out the filter, wash it in hot water with a brush and clear the sump beneath it by hand. Tools: brush, gloves. Time: half an hour. Step two: Wipe the gasket channel and the door edge with a cloth and a mild detergent, working right into the fold. Tools: cloth, detergent. Time: a quarter of an hour. Step three: Run the hottest cycle with a proprietary dishwasher cleaner and nothing in the machine. Tools: dishwasher cleaner. Time: one long cycle. Step four: Lift the air gap cover on the worktop, where one is fitted, and clear any debris from the chamber. Tools: none. Time: a quarter of an hour. Step five: Run a hot programme rather than an eco or quick wash once a week for a month and judge whether the smell returns. Tools: none. Time: a month of habit.
Safety first
Safety
Switch off at the breaker before removing the filter or reaching into the sump, and wear gloves against broken glass. Never mix a chlorine cleaner with any other cleaning product inside the machine. 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 gasket channel has been washed, a hot cleaner cycle has run, the air gap is clear and a drain smell still returns. That points at the drain hose interior or the sink plumbing, which is beyond an owner clean.
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.
