What causes knocking noises in boilers?

Boiler noise results from localised boiling of the water. This happens when the inside surface of the boiler becomes too hot due to scale or baked- on sludge deposits.

All systems over five years can suffer noise and new boilers in old systems are especially vulnerable. Add Fernox Boiler Noise Silencer F2 and / or de-scale the boiler with Fernox DS40 System Cleaner and protect with Fernox Protector F1 or Filter Fluid+ Protector.