Boiler makes loud banging or knocking noises when starting or stopping

Safety: Noisy operation can indicate overheating. Monitor pressure and temperature; switch off if they rise abnormally.

• Bleed system: Bleed radiators and the boiler's air vent to remove trapped air that can cause banging.
• Check pump speed: On adjustable Herz pumps, set the speed or mode according to system design (often medium or auto).
• Descale primary circuit: For older systems in hard water areas, have a technician chemically clean or powerflush the system and, if necessary, descale the Herz heat exchanger.
• Install inhibitor: After cleaning, add a suitable corrosion and scale inhibitor to protect the Herz boiler.