Replaced circulator on gas hot water boiler and still no heat upstairs only in the basement
For making the system work properly you need to follow a few steps.


Make sure that the system pressure is enough to reach the upperfloors.
1 Bar equals in almost 10 m water (Europe)
Make sure that there is no trapped air anywhere in the system.
Therefore you need to find the bleeders on the heaters.
They must be there.
If you are sure that there are none you could carefully loosen the upper pipe connections one by one until air starts to escape and wait until it starts leaking. Then tighten the connection again.
Once you are convinced that none of the heaters and /or pipes contain trapped air you should verify the water pressure in the system.
Verify that the expansion tank is in working order. Knock on it.
If it sounds hollow than the membrane should be good and the tank working.   For this step you need to be sure that there is water everywhere in the system. If the tank is faulty you will start to loose water when it becomes hot. Finally resulting in the same situation you have now.