Worcester Bosch Kettling / Localised Boiling in Heat Exchanger

Boiler makes loud banging, knocking, or kettling noises when heating or producing hot water.

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 restricting flow, Pump running too slowly, Air trapped in heat exchanger

Safety first: Noisy kettling can precede overheating; monitor the boiler and do not ignore repeated lockouts.

Bleed system: Remove air from radiators and any automatic air vents.
Check pressure: Maintain 1.0–1.5 bar cold.
Use inhibitor: If the system has not been treated, have an engineer add corrosion inhibitor after cleaning.
Engineer tasks: A heating engineer should chemically clean or replace the primary heat exchanger, flush the system, and verify correct pump speed.

Hard 4/5

Primary Heat Exchanger

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