The heatsink shouldn't be HOT to the touch unless the fan is not doing its job. However, the heatsink SHOULD be noticably warmer than ambient, especially at the base.
I'm guessing that you moved the mobo from one case to another? It is quite likely that the move jostled the
HSF enough to break the bond of the thermal compound between the
HSF and
CPU. Do like Sam says, pull the
HSF off, clean both it and the
CPU, reapply the goop, and see what you get.