A dishwasher that smells of rotten food or drains is a common complaint in St Francis Bay, where warm, damp canal air speeds up the growth of bacteria and mould. The good news is that the smell almost always comes from one of five places, and you can deal with most of them yourself.

Quick answer

Dishwasher smells come from food trapped in the filter, stagnant water in the sump, grime on the door seal and bottom door edge, a drain hose that lets waste water flow back from the sink, or mould in a machine kept closed. Clean the filter and seal, run a hot cleaning cycle, check the drain hose has a high loop, and leave the door ajar between uses.

Why humidity makes it worse

Bacteria and mould grow fastest in warm, damp conditions with something to feed on. A dishwasher is warm and damp after every cycle, and food residue provides the food. In a dry inland home, the inside of a dishwasher dries out reasonably quickly. In a humid canal home, it stays damp much longer, especially if the door is shut. Holiday homes that stay closed for weeks are the worst case.

Source 1: The filter

The filter catches food. If it is not cleaned, that food rots.

Fix: Remove the filter, rinse it, scrub it with a brush and a little dish soap, and refit. Do this every week or two when the house is in use.

Source 2: The sump

Under the filter is the sump, where water collects before being pumped out. A small amount of water always stays here. If the machine is unused for a while, it goes stagnant.

Fix: With the filter removed, soak up standing water with a sponge and wipe out any debris you can reach. Then run a hot empty cycle. If the machine does not drain fully and water keeps collecting, the drain pump or hose may be partly blocked.

Source 3: The door seal and door edge

The rubber seal around the tub and the bottom edge of the inner door collect grease and food. The wash water does not reach these spots well, so grime builds up out of sight.

Fix: Wipe the seal and the bottom door edge with warm soapy water. Use an old toothbrush on corners and hinges. Dry them.

Source 4: The drain hose

The dishwasher's drain hose usually connects to the sink waste or a standpipe. If the hose is not installed with a high loop, waste water from the sink can flow back into the dishwasher, bringing smells with it.

Fix: Look under the sink. The drain hose should rise up as high as possible, usually clipped to the underside of the worktop, before dropping down to the connection. If it runs straight down to the waste, ask a technician or plumber to fit a proper high loop. Also check the sink trap is not blocked.

Source 5: Mould in a closed machine

If the dishwasher has been shut for weeks in a humid house, mould may grow on the walls of the tub, the seal and the spray arms.

Fix: Clean all surfaces, the seal and the spray arms, then run the hottest programme with a dishwasher cleaner. Repeat if needed.

A cleaning routine for humid homes

After each use:

  • Leave the door slightly open so the inside can dry.

Weekly:

  • Clean the filter.
  • Wipe the door seal and bottom door edge.

Monthly:

  • Run a hot cleaning cycle with dishwasher cleaner.
  • Clear the spray arm holes.

Before leaving the house:

  • Run a hot empty cycle, clean the filter, wipe the seal and leave the door ajar.
  • Close the tap and switch off at the wall.

When it is a fault

Persistent smells after cleaning can indicate:

  • A drain pump that does not empty the sump fully
  • A partly blocked drain hose
  • Water collecting in the base of the machine from a hidden leak

In integrated dishwashers, a hidden leak soaking into the kickplate or cabinet can also cause a musty smell. If cleaning does not solve it, or you see signs of water, call us.

Frequently asked questions

Why does my dishwasher smell like sewage?

Often waste water flowing back from the sink because the drain hose has no high loop, or a blocked sink trap. Check the hose routing under the sink.

Should I leave the dishwasher door open?

Leaving it slightly open after use lets the inside dry and prevents smells, especially in humid homes.

Is it safe to use bleach in my dishwasher?

Follow your manufacturer's guidance. Many recommend dedicated dishwasher cleaners instead. Never mix bleach with vinegar or other cleaners.

Apex HVAC is an independent company and is not affiliated with or authorised by any appliance manufacturer. This guide is general advice. For anything involving electricity or refrigerant gas, use a qualified technician.

Need a hand? See our dishwasher repair service in St Francis Bay.