Regular system ( also known as open vent system or gravity pumped system ) These systems are problematic with sludge & rust (corrosion) due to the open F&E tank in the loft, where the water can oxidise.
This type of system does suffer a lot from sludge & debris within the system & corrosion. We have seen this type of system completely blocked in the pipework due to rust & sludge. Also suffers a lot from pump failure.
Typical faults that a power flush will cure:
Clears cold spots within the radiators, unblock pipework, regain the full flow to radiators and quieten boiler noise. 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.