What every install already includes
A chemical cleanse and long-term inhibitor are on the standard inclusions list for every installation on this site. For a system in reasonable condition, that is the right treatment: circulate the cleaner, flush it through, dose the system, fit the magnetic filter to keep it clean.
When a power flush is the honest answer
A system so heavily sludged that a chemical cleanse cannot shift it needs a power flush before the warranty is valid — it is on our list of costs that are not in the headline price for exactly that reason. The tell-tales are radiators cold at the bottom, repeated pump failures on the old system, and black, thick water at the drain-off.
How you will know
The survey and the state of the system water tell us. If a power flush is needed, it goes into the written quote before you commit — never sprung on install day. If it is not needed, nobody sells you one.
The filter that keeps it clean
Whichever cleaning route your system needs, the magnetic filter fitted on the return is what keeps the new boiler protected afterwards — catching circulating debris before it reaches the heat exchanger. It is included as standard.