yes any car should boil over - mine does now & the HG is fine.

when my HG went i was told to look for bubbles in the coolant when ticking over from cold and the cap off as you described. also white smoke out the exhaust (not just condensation) & oil mixing with coolant in the header tank is signs of HG failure. but im no expert so dont quote me on that!

& the coolant level should be about half way up the tank like the standard items - use a bit of common sense!