Powerclean?

C/Heating Potterton Promax SL 1yr old serving 8 old flat ribbed rads and 3 new convector type, and of course hot water (new tank fitted last year also)
Cost expected to pay for powerclean and time taken. £???
Cost expected to pay for powerflush and time taken. £???

I need amunition to fire at British Gas if I find out my system wasn't done when they supplied and fitted new boiler.
Reason for asking the header tank water is very,very dirty to being manky.