Hello, it's that time of year again, although I did notice this problem last time we had the heating on before summer. The three radiators in the living room, at the furthest end of the house from the Baxi Combi boiler, don't get warm. The one I can easily get to at the moment..the pipe to the raditaor is hot, but the rad is stone cold. It is switched on! After the heating has been on a while, I also get some knocking sound, like water hammer, which goes with fiddling about with various radiators. I did try bleeding one of the living room rads, didn't make a difference. The system was powerflushed a couple of years ago. Can anybody advise please? Thanks.