Boiler shows A03 and shuts down, flow temperature rises rapidly, radiators very hot near boiler, pump noise may be absent.

Safety: Turn off power and allow the boiler to cool fully before touching any pipework. Do not bypass safety thermostats.

• Check system pressure: Ensure pressure is at least 1.0 bar when cold. If low, top up via the filling loop as per the Beretta manual and bleed radiators.
• Bleed air: Bleed radiators and any automatic air vents near the boiler. Air locks can stop circulation and cause rapid overheating.
• Listen for pump operation: When there is a heat demand, listen for the circulation pump running. If silent or excessively noisy, the pump may be seized or air-locked.
• Free a stuck pump (basic): With power off, remove the pump front screw (if accessible) and gently turn the pump shaft with a screwdriver to free it. Refit screw and test.
• Technician – check overheat stat and NTC: Measure resistance of the flow NTC sensor and verify operation of the manual reset overheat thermostat. Replace faulty components.
• Technician – inspect primary heat exchanger: Check for sludge or scale restricting flow through the Beretta primary heat exchanger. Power-flush or replace if severely blocked.