See my post under equipment/techincal - 'best knot for pull throughs'.
I ended up climbing up the first pitch - not too bad, and just as we were about to bag the second pitch the rope popped through. The system is appalling, I know there was talk about having a word with Ralph Johnson, who is the DCA representative, responsible for installing the pull throughs. (correct me if Im wrong anybody, apologies if so).
I think ralph has set them up so there are 2 completely separate systems. (which, I suppose, adhears to most all common advise about belays) However, the system doesnt function very well. There are commecially available systems. with wire and big rings. but these I think only rely on one point of contact (the ring). The one in eldon works fine. (this is a huge ring on a plate bolted directly to the wall.)
but the one in oxlow is the same as the one in nettle and we failed with that too :x .
so its not just you.
PS the passage beyond freeze squeeze and into derbyshire hall is beautiful and relativly well preserved - if you do get in there - please do your upmost to avoid damage to the floor and walls