I've been told that when replacing a boiler it is is a good idea to power flush the system to remove rust and sludge...problem is it seems to be quite an expensive procedure with installers quoting £300-500 on the price of installation, with some saying it is a specialist procedure and don't do it. Would it be effective enough if I removed the rads and ran them through with my Power Wash as a cheaper option?...the system does need it as some of the rads are cold at the bottom end.