The short answer
A musty smell is biofilm on the filter, the door seal and the spray arms, and it clears with a physical clean followed by a hot empty cycle. A drain smell points at the waste pipework or standing water in the sump instead.
Which smell is it
- Musty when the door is opened — Biofilm inside the machine.
- A drain smell that is worse after using the sink — Waste pipework rather than the dishwasher.
- Visible dark film on the filter or the door edge — Confirms the biofilm diagnosis.
- Standing water in the sump between cycles — It sits and goes stale; see the drainage page too.
- A smell that transfers to clean dishes — The film is established and needs a full clean.
- Not this fault: a burning or electrical smell — Stop and read the electrical-safety page.
Ranked for domestic machines
- Filter and sump left uncleaned — First, and the single biggest source.
- Food residue held for days before a cycle is run — Second, and typical of small households.
- Only short, cool programs ever used — Third: nothing ever gets hot enough to clear the film.
- Door seal and door edge biofilm — Fourth, and easily missed because it is out of sight.
- Spray arm ends fouled — Fifth, and it also hurts cleaning.
- Drain hose or waste pipework odour — Last, and it is the one that is not really the dishwasher.
Clean in this order
- Remove and clean the filter and the sump — The largest source, and nothing else works while it is dirty.
- Wipe the door seal, the door edge and the tub lip — The places a wash cycle never reaches.
- Clear the spray arm jets — It improves cleaning at the same time.
- Run a hot empty cycle last — After the physical cleaning, never instead of it.
The reset routine
- Take out the filter and sump strainer and scrub them — Use hot water and a brush; expect more than you want to find.
Tools: brush, glovesAbout 20 min
- Wipe the door seal and the lip of the tub all the way round — A cloth picks up film the wash water never touches.
Tools: clothAbout 15 min
- Clear each spray arm jet and rinse the arms — It addresses smell and cleaning together.
Tools: cocktail stickAbout 15 min
- Run the hottest empty cycle the machine offers — Add a dishwasher cleaner if you have one.
About 90 min
- Run a rinse cycle daily if loads are collected over several days — It stops residue standing at room temperature.
About 20 min
- Leave the door slightly ajar between cycles — A dry tub does not grow biofilm.
Cleaning safely
Safety
Unplug the appliance or switch off its breaker before removing any panel. A capacitor can hold a charge after the power is off. Wear gloves, and never mix dishwasher detergent or cleaner with bleach or any acidic descaler - the combination produces dangerous fumes in a confined kitchen. Let the machine cool before reaching in after a hot cycle.
When to call
Call when the smell survives a full physical clean and a hot cycle, because the remaining sources are the sump, the drain hose and the pump housing. Call a plumber if the smell is of drains and the sink smells too, since the two share pipework. A machine that holds standing water between cycles has a drainage fault and should be read on that page first.
Other pages here
Scope
Generalized across dishwasher families under this badge rather than for a model line; where a family-specific or model-specific page exists it is the narrower answer. Not here: cleaner brand names, program temperatures, filter part numbers and waste pipework standards.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
