Hi all,got to change a rad soon for my brother(freebie).Its quite an old system with a back boiler,so i was thinking of hiring an electric pipe freezer,draining rad and replacing valves before fitting new rad .i don`t really want to drain the whole system but if the advice is that i should then i will.also what would be a good treatment to put in if i only drain the rad.thanks for any advice,malc.