Boiler descaling

I have an Apollo 80B and it is making a lot of noise, I have been told it is scaled up and wondered if anybody knows how to descale.
will the descalers that are added to the expansion tank actually work?
I was thinking of adding limescale remover to the heat exchanger once I have removed it from the boiler.

TRy the "boiler descaler" which as you say goes in the header. Takes a while to get round unless you drain some water out to let it in. Sometimes 2 goes are worthwhile.

Something like Sentinel X200 or the Fernox one can be left in thesystem. These are not the same as system desludgers, which have to be flushed out.