We have one cold radiator in a central heating system with a primatic cylinder (no header tank). We have flushed the radiator - worked for a short while. The radiator is cold even though the incoming pipe is hot. With left hand valve shut and right hand valve open, opening bleeding valve still produces water pressure and vice-versa. It has been suggested that we completely drain the system to remove any existing buildup of detritus. The radiator affected is furthest from the pump. Boiler has been kettling and Fernox additives have been successfully used via one of the radiators
Any suggestions will be gratefully received - we are looking forward to a warm room for our Christmas dinner (LOL).