Check you’re storing it properly – it’ll be sticky or hard if damp. If it’s okay, the drawer’s water jets may be blocked. A water softener (eg Calgon) will help protect the heating element and other parts, but won’t stop limescale forming on the jets if you have hard water. To clean, mix equal parts clear vinegar and water. Remove drawer and scrub the solution on to the compartment roof, then run an idle wash (empty drum, hottest programme, maximum dose detergent).