The thermostatic valve on one of my radiators appears to have stuck open. On the other side I've got this:-
I tried turning it 90degrees (the brass stem on top) thinking it was a ball valve to stop the flow, but the radiator still hasn't cooled down so I assume that's not enough. Is that some sort of valve that I can close to turn the radiator off?

I tried turning it 90degrees (the brass stem on top) thinking it was a ball valve to stop the flow, but the radiator still hasn't cooled down so I assume that's not enough. Is that some sort of valve that I can close to turn the radiator off?