Steam heating system radiators, not effected by valve position?

I have a heating system in a building and the wall heaters which have very hot steam going through the pipes aren't effected when the control valve is shut. I suspect the valve may not be closing to the individual heaters. Because the area they are in is locked off I can't readily check this. I suspect they are working however because the radiators make a different sound depending on the control voltage applied, On/Off. They are louder when they are open. Both positions the radiators emit very hot. I tried leaving the valves in both positions and

Now, where the radiators are closed they are always emitting heat. Very hot. They are so hot and they are heating the room so much to the point where the windows have to be open, even when the valves are closed. What is the point of even controlling them if it's not going to have any effect to the process. The valves are pretty close to the radiator, about 1 meter of piping away. I think that distance might also be a problem. The valves can't be moved further back in the supply line, so I think even the position change wont't do anything. What can be done to make this system more controllable? Should there be a control valve on the return side of radiator aswell?

Thanks!

Replace the valves.

They are probably getting steam-cut at the seats.

Or, add a (steam rated) actuated ball valve ahead of the control valve to completely isolate the line when no heating is called for.

it takes about 1 hour to cool down. maximum pressure of radiators is 4 bar. so dont go to hard.
a water heating system is max 90 celsius so reducing the heater would be the first thing.
when the valve closes the radiator will fill up from the return with condensated water, giving a lot of heat.