Our previous house (forced air) didn't have this problem, but now (in hot water heated house) the bedrooms (2nd floor) are always too hot even with the radiators completely off. After a whole night of setback in this cold weather, downstairs is 63 (the thermostat setting) while the bedrooms have barely dropped to 70.
The radiator valves don't leak. The thermostat is on the first floor and is controlling the temperature there quite well.
My theory is that with forced air, the air is pulled down through returns and recirculated, while with radiators, the warm air has nowhere to go but up. We do have a largish, open (door-less) stairway.
Is there some other possible reason? Is there anything to be done except sell and move?