Monsoon pump working - but no hot water

[Coldwarkid]

Monsoon 3.0 bar pump to hot water taps in our loft extension bathroom packed up - the maufacturer Stuart Turner fixed it (very good service I thought) but now I have put it back on just as it was but taps are bone dry still.
Pump is spinning to pressurise itself and pipes in and out weren't blocked when pump ws removed so assume are ok now; rest of system is fine.
It's driving me mad because it SHOULD work but doesn't - anyone got any ideas?

 

[Gasguru]

Hope you've primed it before turning on.

 

[Coldwarkid]

Yes, and there was some water out of the priming valve but not under any pressure - which us odd as I checked the pressure and that was fine......