System Boiler ( sealed system)
With a System boiler you do not have cold water storage but you do have a hot water cylinder.
The system boiler suffers from scale just like a kettle. When this happens the boiler makes a noise very much like a kettle boiling or a banging noise. Also the pump in the boiler fails. The radiators still suffer from sludge but not as much as the regular boiler known as the open vent or gravity pumped system.
Typical faults that a power flush will cure:
No hot water, Boiler lockout or breakdowns, loud banging noise's from boiler & boiler overheats and goes into fault mode. Cold spots in radiators or radiators not working at all no heat.
Also remember when fitting a new boiler you must have the system power flushed before new boiler is fitted. This will invalid your warranty if no power flush is done.