Unplug the machine from the mains completely. Lay towels across the floor in front of the machine and place a shallow tray beneath the filter access flap. Even though E21 indicates slow drainage rather than no drainage, water will still be present in the drum and hose.

Open the access flap and position your tray beneath the filter cap. Turn the cap anti-clockwise by a quarter turn to begin releasing water slowly into the tray. Empty the tray, then continue unscrewing until the cap comes free. Pull the filter out fully. Rinse it under warm running water, scrubbing the mesh with a toothbrush to remove all lint, hair, fabric fibres, and debris. Reach into the filter housing cavity with a torch and clear any debris from around the pump entrance.

Shine a torch into the empty filter cavity and locate the impeller at the rear. Rotate it gently with one finger. It should spin with smooth, even resistance through a full rotation. Any catching, grinding, or intermittent stiffness in one position indicates a partial obstruction around the impeller blades.

Trace the drain hose from the machine to the standpipe or sink waste connection. Straighten every kink, sharp bend, and compressed section along its full length. Confirm the hose end is inserted no more than 15 centimetres into the standpipe, is not sealed against the pipe walls, and that the hose has an upward loop reaching at least 60 centimetres above floor level before descending to the waste connection.

With the machine unplugged, remove the rear lower access panel if fitted. Inspect the short rubber hose between the pump outlet and the main drain hose for any collapse, kinking, or compression that would restrict the flow path out of the pump.