How do I power flush my heating system?

A cold radiator didn't require bleeding, no air in the system at all, and I was advised that the radiator might be sludged up or the system needing a power flush. I've removed the offending radiator and flushed it through, the water was clean when I emptied it and clean while flushing it through. When I reconnected the radiator, repressurised and bled the system I now have three cold radiators? So I'm thinking that a power flush is required but can I do this myself and if so, how?