Lets face it, whether you flush or powerflush a system, if it isn't clean when you fit a new boiler you will end up with a lot of problems. I'm starting to actually use my power flush machine when I change a boiler as I can leave it running with the magnacleanse attached but thats my personal preference and I include it in the price, some guys just do a hot and cold flush which is equally acceptable as long as the system is clean. Its the yeehaws that rip an old boiler out and fit a new shiny one without any flushing at all that's the problem. oh and BG charging £600 for a powerflush is criminal in my book, most I would get away with is £300.