The spray arms and the places water never reaches
Spin each spray arm by hand. If it stutters or sticks, it needs attention. Most unclip or unscrew by hand — check which before you force anything. Hold each arm up to the light and look at the jets: limescale and seeds block them, and a blocked jet means an entire corner of the top rack simply isn't being washed. Clear each hole with a cocktail stick or a straightened paperclip, then rinse the arm through under the tap.
Next, the door. The rubber seal around the opening collects a dark, tacky line of residue that smells long before it looks bad. Wipe along it with a damp cloth and a little washing-up liquid, then use a toothbrush along the groove. Do not forget the lip at the very bottom of the door and the ledge beneath it — that strip sits outside the wash and never gets rinsed, so it is usually the actual source of the smell. Finish with the detergent dispenser flap and the cutlery basket, which quietly hoards gunk in its slots.
The empty hot cycle, and the hard water question
With everything clean and reassembled, run the machine empty on the hottest programme it has. Many people add a bowl of white vinegar on the top rack or a shop-bought dishwasher cleaner; both are common practice, though some manufacturers advise against acidic products because of the seals, so it is worth a glance at your manual first. Citric acid is the other traditional option. Whatever you use, do it on an empty machine and never together with bleach-based products.
