Bosch Boiler Kettling / Noisy Heat Exchanger

Boiler is noisy during operation; banging, kettling, or whistling sounds from the unit.

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 in system reducing flow, Pump running too slowly, Air in heat exchanger

Safety: Turn off power and allow the boiler to cool before bleeding or opening any components.

Steps:

Bleed radiators and any automatic air vents to remove trapped air.
Check system pressure and top up if low.
If noise persists, the primary heat exchanger may be scaled or sludged. A powerflush or chemical clean of the system and/or heat exchanger descaling is recommended.

Descaling and powerflushing should be carried out by a heating professional familiar with Bosch boilers.

Hard 4/5

Primary Heat Exchanger

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