Hi and thanks for getting back me! There are 2 other radiators in parallel with the cold attic one. So I think the answer is that it is not in a different zone. One other piece of info, I looked at the pump and it seems to be cranked all the way up, so perhaps someone else realized this problem. (I bought this house just last year).
I can get heat from the attic rad if I turn it way up, but not under normal circumstances.
My guess is that the pipes leading up there are clogged. They are unfortunately behind walls where I can't see them.
Let me know if there are any other ideas, or suggestions on how to deal with clogged pipes.