Washer-dryer attempts to fill but then stops and shows F04; may also drain immediately after filling.

Safety: Unplug the appliance and turn off water supply.

Steps:

• Access pressure switch: Remove the top cover. The pressure switch is a round plastic device with a small rubber hose attached, usually mounted on the side wall.
• Inspect pressure hose: Check the thin rubber hose for kinks, splits, or blockages. Detach it from the switch and gently blow through it toward the tub; it should be clear.
• Clean pressure chamber: At the tub end, the hose connects to a small pressure chamber. Detach and clean out any soap scum or debris that may block air flow.
• Test switch: With the hose attached, gently blow into the switch and listen for clicks. Using a multimeter, verify that the contacts change state when pressure is applied (refer to Ariston wiring diagram).
• Replace if faulty: If the switch does not click or contacts do not change, replace the pressure switch with a compatible Ariston part.

Warning: Do not run the machine with a bypassed or faulty pressure switch; overfilling can cause flooding.