Cold Radiatores Up Stairs

[tomj2450]

I recently removed a radiator on the first floor to remodel the bathroom.
Idrained the system removed the radiator after completing the work i replaced the radiator. (7 radiators on first floor 2 on second floor)
Refilled the system I have not heat on the second floor the radiators upstairs have water but it seems that the return flow to the boiler is not working. I have bled all radiators numerous times. Can someone out there give me some ideas.

 

[JPC]

try draining down some water from the system via a drain valve...this might dislodge what is probably an airlock.

similarly, close all rads but 1 of the none working ones and see if that shifts it