Water heater shuts down with A03; unit becomes very hot before locking out

Safety: Turn off power and allow the appliance to cool completely. Do not bypass any safety thermostats.

• 1. Reset after cooling: Once the unit is cool, reset it. If A03 returns quickly, there is likely a circulation or heat exchanger blockage issue.
• 2. Check system valves: Ensure all isolation valves on the heater's flow and return (or inlet/outlet) are fully open. Closed valves will cause rapid overheating.
• 3. Inspect circulation pump (if fitted): On Beretta combi/boiler-type water heaters, listen for pump operation when there is a demand. If silent or very hot to touch, the pump may be seized or air-locked.
• 4. Bleed air from system (technician-level): Air in the primary circuit can cause overheating. Use the automatic air vent or manual bleed points as per Beretta instructions.
• 5. Check and clean primary heat exchanger: Limescale or sludge can restrict flow. A technician can remove and chemically descale the Beretta primary heat exchanger or flush the system.
• 6. Test safety thermostat and NTC sensor: Using a multimeter, a technician should verify continuity of the overheat thermostat and resistance of the NTC temperature sensor. Replace if out of specification.