A dishwasher is the one appliance we assume cleans itself, on the reasonable-sounding logic that it is full of hot water and detergent several times a week. It does not. Grease, food debris and limescale build up in exactly the places you never look, and the first sign is usually cosmetic — a film on the glasses, grit in the bottom of a mug — followed shortly by a smell that meets you when you open the door. The good news is that a proper reset takes about twenty minutes of actual work, most of which is standing at the sink.
Start with the filter, because that is usually the whole problem
Pull out the bottom rack and look at the base of the machine. In most dishwashers you will find a cylindrical filter that twists out, sitting inside a flat mesh plate that lifts away with it. If you have never removed it, brace yourself: this is where everything that did not drain away has been sitting.
Take both parts to the sink, rinse under hot running water, and work through the mesh with a washing-up brush or an old toothbrush and a little washing-up liquid. Grease clings to the mesh even when it looks clean, so give it more attention than seems necessary. Rinse thoroughly, check the well underneath for stray fragments — olive stones and bits of foil are common culprits — and refit the filter properly, turning until it locks. A filter that is not seated correctly lets debris circulate straight back onto your dishes.
