Open the fill valve then open one of the upper floor's bleeder valve until you get water out. Repeat at the other bleeders upstairs. Once you've got all the air out, you should get circulation. It doesn't take much air to block flow when it needs to go up. Once almost all of the air is out, the air extraction system should pull the rest out as it circulates around as microbubbles.
The pump in most systems doesn't have a lot of head - it takes the full system being full of water with some of it pushing back down to help it flow all the way around. then, since it is a closed system, the low powered pump can keep it flowing.