I have have a new installation with 3 zones each fed with their own zone pump. It seems that in the upstairs zone there isn't much heat comming out of the BB even with 160* water. I am thinking tht perhps there is air in the line. I do not hear any noise of water running. I just cleaned all the BB removing dust and dog hair. The BB are in the order of 30-40 years old. Do they tend to loose the ability to raidiate heat with age?