** i assumed that by doing so, the heat that normally went to that bedroom would be shifted down to the lower main floor in some way **
Where is the thermostat controlling the boiler?
If on the main floor, the main floor rads should always heat to the same temperature regardless of what heat is generated by rads elsewhere. Once satisfied there, the thermostat should shut the boiler off. Reducing the number of rads which don’t directly affect the main thermostat would just reduce the run time of the boiler, not produce any ‘extra’ heat.
The system might be able to be balanced so only an appropriate amount of heat is circulated to the upstairs rads while the main floor stayed at your set temperature (controlled by the thermostat).
It is also possible for thermostats to be attached to individual rads so each can actually be controlled separately aside from the main thermostat control for the whole boiler.
JMO
Dan O.