In reply to mypyrex:
> I've turned the thermostat(?) at the end of the radiator right down but does this actuall stop the flow of water into the radiator?
It should do if it's working, you also need to shut the valve on the other end of the radiator, to isolate it from the system. Take the cap (usually white) off and use a spanner.
Edit: see above, I must be slow typing today
Post edited at 11:30