issue with closed loop hot water heating
If the radiators are in series, bypass valves in the basement to adjust the energy flow by &quot;short-cutting&quot;  would be a solution.
Sometimes the size of the radiators are adapted to the hot water flow in old systems.
Also a flush of all radiators can help to improve the throughput - sometimes they are clogged with metal oxides and dirt like old car radiators.
If the first radiator is only hot in the upper part, and cold in the lower part, it could be also a failure of the pump (blocked by the dirt in the system) resp. the capacitor of the pump. Often this capacitor is defect thus blocking the pump from running on its nominal power. This can even happen with new pumps.
A photo of the pump might help to identify that probability.
Air bubbles in the radiators are another reason for cold radiators.
Could be easily checked by the bleeding valves. Thus the color of the water can be seen (f.e. in a white cup).