Thanks to all.
And thanks simond, your advice to open up the boiler front to access the pump auto vent and unscrew the black cap solved it, air gushed out. That cleared the pump and fired up the boiler.
I didn't know I could open the boiler without treading in RGI territory. The rest from there was fill and bleed. I have now run the heating a few times then let it settle to bleed off air, mostly on upper floor rads. It reads 1.5 bar and hopefully can stay there.
>> Filler Loop - I keep on about the filler loop because it confused me greatly, and I take your point Dan. As it is I can't drain water off for things like this because of where the non-return valve is, it is on the heating side and therefore won't allow water back out of the system.
But, that is how the new R24 filler loop from
Screwfix was assembled, exactly as in the picture. To do as you advise I would have had to take off the flex hose from the NRV side and swap it around to the other side of the same valve, same thread no problem. Then fit that assy wth the NRV the correct way round on the cold feed side. In turn then swap the other valve currently on the feed in over to the heating side, then fasten the flex hose to both.
It's not rocket science and is logical now I look back at it. BUT..... I wouldn't assume that a filler assembly would need taking apart and reversing in order to achieve that.
I think the old loop that had been leaking, although showing an arrow of direction, maybe wasn't actually a NRV. When I blew through it there was no resistance, it allowed air to be blown through it in both directions.
I will leave it all alone for now as the system seems fine. If I need to drain down again I will swap it all over as described above.
Thanks again to all, got me out of a fix.
It's easy when you know how - and I didn't! And everything is obvious .... to the man who knows.
All the best, thanks a lot.
