Individual radiator thermostats dont turn off ?

I have set each radiator thermostat to off in unused rooms, despite this they are burning hot. The only way i can turn them off is to turn the whole heating system off at the boiler. I dont have any room thermostats just the ones on each radiator. Is there anything i can do to fix the problem, it just suddently happened the other night after i tried to bleed one of the radiators, a lot of air hissed out but still no heat getting through to that one at all. Its a pretty old boiler.