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A powerflush is without a doubt the best way of cleaningout sludge and rust from heating systems, radiators and boilers. It's been around for years now. I think the first guy to build a powerflush pump was Keith MacBain , a former British Gas engineer who left BG to start his own business making powerflush pumps.
Although it's a great way of sorting out problem systems there are some potential hazards for the unwary or inexperienced poweflushing engineer. For a good reliable company that offers free advice to anyone you can take a look at this powerflush site.