Boiler makes loud banging or knocking noises when starting or stopping

Safety: Allow the system to cool before touching pipework.

• Bleed radiators: Remove trapped air from all radiators and the pump (if it has a bleed screw). Top up pressure as needed.
• Check pump speed: If your Ariston pump has adjustable speeds, try lowering the speed to reduce water hammer, especially on small systems.
• Secure pipework: Inspect accessible pipes near the boiler and around the house. Add or tighten pipe clips to prevent movement when the boiler starts or stops.
• Descale heat exchanger: Kettling (boiling) noises from the boiler indicate limescale. A professional can descale or replace the primary heat exchanger.