Machine displays ALARM 4; steam boiler does not fill or overfills, and autofill cycles abnormally.

Safety first: Turn OFF and unplug the machine. Allow the steam boiler to cool and fully depressurize. Open the hot water tap to relieve pressure.

Corrective steps:

• Verify water supply and pump: Confirm that the incoming water supply is on and that the pump is capable of building pressure. A starved pump can mimic level faults.
• Inspect steam boiler level probe: Access the steam boiler and locate the level probe (single insulated wire on a threaded stainless rod). Ensure the connector is tight and free of corrosion.
• Descale the probe: Remove the probe after draining the boiler to below probe level. Soak the metal rod in descaler to remove limescale. Rinse thoroughly and reinstall with a new gasket if needed.
• Check the steam boiler fill solenoid: Locate the solenoid feeding the steam boiler. With the machine calling for fill (for trained personnel only), listen for a click and feel for vibration. If the coil energizes but no water flows, the valve may be blocked with scale or debris.
• Clean or replace solenoid: Isolate water, depressurize, then remove the solenoid valve. Inspect and clean the internal plunger and orifice. If the coil is burned or the valve body is damaged, replace the entire valve with a La Marzocco-compatible fill solenoid.
• Check wiring and board: If the probe and valve are functional, inspect wiring continuity to the control board. A failed autofill relay or board circuit will require professional service.

Do not operate the machine with the level probe disconnected, as this can cause dangerous overfilling and water discharge through the safety valve.