Protherm Kettling Due to Scale or Sludge in Heat Exchanger

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

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Limescale build‑up in primary heat exchanger, Sludge accumulation in system water, Low flow rate through boiler, Incorrect system balancing

Safety: Turn off power and gas. Allow the boiler to cool before touching pipework.

Steps:

Check system pressure and bleed air from radiators and boiler to ensure proper circulation.
Ensure all valves are open and that the pump is operating correctly.
Install or clean existing system filters to remove sludge.
A qualified technician can perform a chemical descaling of the primary heat exchanger or a full system power‑flush to remove scale and sludge.
If kettling persists after cleaning, the primary heat exchanger may need replacement.

Hard 4/5

Primary Heat Exchanger

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