Hi, hope you knowledgeable folk can help as I’m a total novice when it comes to plumbing. I’ve got 13 radiators in my house and a few of them are not heating up. At the moment when going into Bedroom 3 on the g/f is like walking into the artic. If however I turn off 10 radiators (numbers 1 – 10) at the TVR side (right side when looking straight on) then the remaining 3 radiators (11, 12 & 13) start to warm up. I’ve bled all the radiators and the only one that ever seems to have any build-up of air is Radiator 1. The house was extended/ensuite added a few years before I purchased it and additional radiators were added at the time to the newly created areas (not sure if the pipe work to them was run from the manifold which is on the 1st floor or the supply taken from the nearest older radiator). I should add that my central heating system is actually a mix of microbore and normal pipes. 7 radiators on the g/f (4-10) have microbore pipes. The three problem radiators (new ones) all have normal pipes. Also all 3 radiators on the 1st floor also have normal pipes. Last night I tried to establish which radiators come on first and played around with their lockshield valves. Currently 10 Radiators (numbers 1 – 10) have their lockshield valves open a ¼ turn. 11 is open ¾ turn, 12 is open 1.5 turns and 13 is fully open. Prior to me doing this radiators 11,12 & 13 were stone cold. So my tinkering around has been of some benefit as 11 & 12 are heating a little (13 is still stone cold). In the diagram I’ve numbered the radiators in the order which I believe they warm up first (with the exception of number 3 on the 1st floor which may be feed from down below, number 11). I’ve also put in a percentage of how much of the radiator gets hot (from top downwards). What do I need to do to get radiators 11,12 & 13 working again? Appreciate any help.