I assume you have opened the mains water grey handle rught hand side,not the grey handle in last photo. As the boiler is unpressurised and at high level i would expect no water,well very little from the left side valve when opened. The mains inlet grey valve,i assume you are turning it clockwise.Quarter turn only.
so if I am correctly understanding your post , you have taken the grey plastic handle off ,and used a spanner on the square end shaft below ,you have opened the valve ,and water comes out of the boiler ( where the hose goes on ) if so connect the filling loop hose and open the right valve and left one with a spanner and it will fill.
The valves are limited to quarter turn. Everyone relax, I am opening the correct valves at the correct time. The main reason for asking the question was to check there wasn't some sort of pressure cylinder or control system that might be blocking input for some reason. If it's only likely to be a valve issue I can with it out. Cheers for the help anyway.
No. If you look closely, it's not immediately visible in the last photo, opposite the grey valve there is a drain cock and square shaft headless tap. I've tracked down the part and part number so now I just need to find one as cheap as possible and swap it out. Hopefully I can get it locally as I half expect to be able to revitalise this valve unless something is snapped. Fingers crossed. I'll let you all know how I get on but it'll be next weekend. Off to the film set all week so no heating for the family til then. . (wear a jumper!!)
now I got you. try taking the screw out the left hand grey handle ,then remove the handle .beneath should be a squarish shaped shaft that you can turn with a spanner to open.it may be that the plastic handle is not actually turning the shaft.
platypus ,you mentioned that you were OK with plumbing. you could introduce water into the system via a radiator / hose to outside mains pressure tap and a double check valve if needs be.
Dear Platypus your post was 4 years ago so its rather a shot in the dark, but hey ho, here goes. I had EXACTLY the same problem - same boiler, same no flow with the loop. I went through the same process as you - ie disconnect the hex nut on the heating side and the water flowed fine, so some kind of blockage heating side. British gas came and fixed it but of course i was out and they left no clues nor can i find a way of getting through to the engineer! Ion return i rushed to the boiler to see and the pressure was up but the loop still silent - i have no idea what he did ( my wife wouldn't have helped in this) SO my query its - did you manage to diagnose the problem in the end? Thanks = my curiosity is killing me