Boiler making loud banging or knocking noises during operation (kettling)

Safety: Kettling indicates overheating; do not ignore persistent loud noises.

• Check system pressure and flow: Ensure correct pressure and that all valves are open to allow adequate flow.
• Bleed air: Remove trapped air from radiators and boiler vents.
• Water quality: If in a hard water area, the primary heat exchanger may be scaled. A technician should chemically descale or replace the heat exchanger following Viessmann procedures.
• System flush: Have the heating system power-flushed and inhibitor added to prevent further sludge and scale.