So I've taken my lounge radiator off to strip the old paper, and there's a bit of a drip from one of the pipes, as well as gallons of black gunk in the radiator, now flushed out in the garden.
In my loft there's a wee tank next to the big tank. I turned off the water into that, then shoved a bit of garden hose into one of the bits were the radiator joined the pipe, and opened the valves again until the alternatively black then rusty water stopped. So I guess that's my CH system mostly drained (so the leak can be fixed) and because 1) I've already got a radiator off and 2) they were evidently full of crap, this would seem like a good time to clean the system and refill it with some of that magic potion added.
Am I right in thinking I can do it all from just the one room? Shutting off all the radiators and just opening up one at a time, or keep them all open? And probably best to refill the system and add some cleaner stuff for a couple of days first?
What am I missing?