Thanks for all you help chaps. As I suspected, just tested the mid pos valve and it's up the creek. Easy fix then. Oh and by the way boys you don't need loads of certificates to tell whether you have any intelligence. I've seen what some of you so called experts have done in the past and it's one of the reasons I do it myself, the other reason being that because I'm not a plumber/ CH engineer by trade I make sure what I do is to the highest standard. I've even been asked to put right some of the stuff some of you bodge it and scarpers have left behind. Your not brain surgeons your
tradesmen.
Yes it shows by your ignorance in your posts