I have had to drain the primary of my c/h system (2-pipe) for repairs.
Since refilling I get no flow in the upstairs rads. Downstairs rads. are balanced and practically shut-down. Upstairs have all valves fully open. Domestic hot water just fine.
Sounds like an airlock in the hot feed to the upstairs circuit (separate from downstairs circuit).
Anyone got any ideas of how to go about clearing this? Ta.