have primatic central heating (cold water tank in loft feeds toilet. mains house. have hot water cylinder in kitchen. potterton gas fire with back boiler. have powerfushed system.individual theromstatic controls on all but bathroom radiator which has none. all radiators work except one in daughters bedroom. when i feel the feed and return pipes connecting to this radiator one is stone cold and the other is very hot. i have replaced some old radiators as they were tatty and have bled all and they seem ok.i have a danfoss pump under the floor.system has been microbore and installed for about 15yrs as it was originally coal central heating which was changed to gas about 8yrs ago so pipe work is original although most radiators have been replaced. i also have a new should be heated towel radiator on bathroom wall which my hubby is terrified to fit as he needs to drain the sytem and is worried about how to do this as he said something about an air bubble. he is superman otherwise and very skilled at most diy. any ideas please. If i can get this solved i will promise to send you a gift.