Boiler makes loud banging or knocking noises when starting or stopping, sometimes called kettling.

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

• Bleed air: Bleed radiators and any automatic air vents to remove trapped air that can cause noise.
• Check system flow: Ensure all valves are open and that the circulation pump is operating correctly.
• System cleaning: Have a professional perform a chemical flush of the heating system and, if necessary, a targeted descaling of the Rinnai heat exchanger.
• Install filter: Consider adding a magnetic or dirt filter on the return line to protect the boiler from sludge.