Vaillant thermocompact 615e- no heat to rads, please help!!!!

[Savva]

I was called to the property having been told the boiler was leaking. The system had no pressure in it but surprisingly the heating WAS working. The leak was the AAV which was an easy fix, pressurised the system which flew straight out the prv so removed boiler and changed the exp ves. Put it all back together & pressurised the system, so far so good. However, now the flow doesn't reach the rads!!! The heating two port seems to work ok, the pipe either side is hot but none of the rads are receiving any heat. Customer has a family, really want to put it right for them. Any ideas??? Much appreciated.