Boiler lights but then shuts down quickly with error A02; may show signs of overheating such as very hot flow pipe and noisy boiling sounds.

Safety first: Turn off power and allow the boiler to cool fully before touching any pipework.

• Check system pressure: On sealed Ferroli systems, ensure the pressure gauge reads around 1.0–1.5 bar when cold. If low, top up via the filling loop according to the manual and bleed radiators.
• Bleed air: Bleed radiators and any manual air vents near the boiler to remove trapped air that can cause localised overheating.
• Verify pump operation (user observation): With the casing on, turn the boiler back on and feel the flow pipe; it should warm gradually, not instantly boil. A loud kettling noise suggests poor circulation.
• Engineer checks:
  • Confirm pump is running and not seized; replace the circulation pump if faulty.
  • Check and clean the primary heat exchanger for scale or sludge blockage.
  • Test the overheat thermostat and flow NTC sensor; replace if readings are out of range.
  • Flush the system and add inhibitor to prevent future sludge build-up.