In message , Kalico
writes
A 6 month old combi boilered system, plumbed in mainly plastic pipe.

About two months ago I got a problem with the hot water (DHW) not
flowing hot enough.

I called the boiler engineer (under warranty) who said that the heat
exchanger was blocked with metal flakes that must have come from the
inside of the radiators.

Is it a complete new system or just a new boiler (sorry, I might have
cut too much of your post)

If a complete install, then the responsibility lies with the installer,
since this is who you have a contract with

unless you bought the bits yourself

otherwise, the installer should have cleared out the system, so again,
prolly his responsibility
--
geoff