If it's hot and there's no pressure in the radiator (known by squeezing the top hose), then you've got a leak but not only that, your boiling point is a bit lower.
It's either going to be a faulty radiator cap which is easy to check
The seal on the pump that's gone.
But you need to check for loss of coolant first because any leak anywhere will give a loss of coolant.
Worst case situation is that the head gasket has a leak internally, if it's going to happen, it's going to happen when you push the car hard, cylinder pressure will push coolant out of the cap, when you shut it down, you've lost coolant so there's no pressure in the rad.
The next thing that happens is that due to excessive pressure in the cooling system, coolant gets forced part the pump seal, the bearings rust, then the pump seizes, taking with it all 24 valves.
It DOES happen.
If you catch it early enough, it's an easy fix by re torquing the heads.
quote from barryboys.
Yes, yes, yes, that might be so, but you're clearly missing the bigger picture.....