Thanks for the suggestions so far, I can't re-check any of it 'til next weekend , but will try the suggestions made.


The pump and boiler had almost certainly been running but idle when I first opened the bleed, but I did go and set the 'stat on cos I thought it might bring on some pressure to get some more air at the bleed but it didn't.
The pump was running when I had the whole nut removed!.

And for information, the pump and boiler are on the ground floor , (this rad is upstairs).

Thanks in advance for any more ideas

I just don't understand how water can defy gravity and be pushed out in the roof space overflow rather than coming up to the top in the actual rad when it was open to the air ??