As per Alex's first reply those are the possibilities,
I'm more interested in why it got hot the first time - no leaks - high pressure - in hoses - hot air when revving then I bet it goes cold and the heater gauge goes up?
I have seen those symptoms 3 times now, one was a new engine install and was an airlock - one was again an air lock but no idea why it got it the bad news is the third was a blown head gasket.
Check for oil in the water and water in the oil do a bleed - I use a coke bottle with some amalgamating tape and jack the front up - so similar to that link but without the fancy funnel
Doubt it's water pump maybe a blocked rad so maybe a good flush through is worth a try - you can take the thermostat out completley and run like that as a test.
Hope you get it sorted quick and easily