We had one done earlier this year by British Gas. We have a 5/6 bed house...had a powerflush,magnetic filter thing and some extra pipe work done. It was all carried out in a day very efficiently and cleanly. Boiler is a Valiant Ecofit Pure. Oh,and also a hive controller/thermostat and box.
All in £3.2k give or take a couple of quid plus BG give you the homecare cover for a year so that saved me about £350 which makes the actual figure just under £3k