I have a radiator in the dining room that has never worked properly. Its not bunged up, and has no air locks. The the pipes run from the up stairs bedroom down to this rad and to make things worse the are of a smaller bore. My question is thi ,can I take a spur off the radiator in the hallway, or should i try an renwew the pipes from the bedroom which of course are buried into the wall by the previous bodger!