Old Cast Iron Radiators and Forced Hot Water (Shut off valve question)

Hi All: I have an old heating system. It is a Forced Hot Water System with those old cast iron (about 30" tall) under every window. They are not recessed in the wall. Each of the upstairs radiators has a shutoff valve. It is my understanding that the valves only partially shut off the radaitor. Lately I notice that the tmeperature upstairs gets really hot and downstairs is cool. I tried shutting these valvles and most are hard to turn and I'm afraid I wil brake one or cause leakage. Anyone have any experience with these radiator valvles? The last thing I need now is to break one of these in the middle of the winter. M

You are probably better off waiting until heating season is over and then try to do something with them.

Patience! It's only a few weeks away......