Machine displays ALARM 2 and brew boiler does not heat or overshoots temperature; temperature reading is unstable.

Safety first: Switch OFF and unplug the machine. Allow the steam boiler to cool and depressurize fully before removing any covers. Open the steam valve to release residual pressure.

Diagnostic and corrective steps:

• Visual inspection: Remove the top/side panel to access the steam boiler. Locate the steam boiler temperature probe (threaded sensor with two wires). Check for leaks around the probe, corrosion, or broken wires.
• Check connectors: Ensure the probe connector is firmly attached and dry. Reseat the connector at both the probe and the control board.
• Check cable integrity: Look for melted insulation near hot surfaces or sharp bends where the cable may have broken internally.
• Resistance test: With the machine unplugged and the probe disconnected, measure resistance across the probe. Compare to La Marzocco specifications at room temperature. Replace the probe if readings are out of range, open, or shorted.
• Reinstall or replace: If the probe is faulty, install a new La Marzocco steam boiler temperature probe. Use appropriate thread sealant if specified and tighten to the recommended torque.
• If problem persists: If a known-good probe and wiring still trigger ALARM 2, the main control board’s temperature input may be defective. Contact an authorized La Marzocco service provider for board diagnostics and replacement.

Never operate the machine with the probe disconnected or bypassed, as this can cause overheating and boiler damage.