Assuming you left the rad cap off when initially bleeding it? if not may be thermostat.

Rich

We ran it very hot to a point when I was scared to keep it running.
Do you mean running it with oil filler cap off? Expansion tank cap was off anyway.

Here's another issue:
Top of the thermostat circlip just happens to be aligned in such a way that neither Keith or I could reach it with the circlip pliers. So somehow, the circlip has to be pushed around, or the whole pump taken off. Just for clarification, does the circlip squeeze inwards or outwards to remove?

How do I check circulation?

Thanks Mike and Jim. Jim I am especially happy with your confidence there! Do you think a pressure tester on the expansion tank would help at all?

We ran it very hot to a point when I was scared to keep it running.
Don't run the engine that hot because if the coolant isn't circulating through th radiator then your electric fans won't switch on.
Do you mean running it with oil filler cap off? .No I mean the coolant filla cap Expansion tank cap was off anyway.

Here's another issue:
Top of the thermostat circlip just happens to be aligned in such a way that neither Keith or I could reach it with the circlip pliers. So somehow, the circlip has to be pushed around, or the whole pump taken off. Just for clarification, does the circlip squeeze inwards or outwards to remove?

How do I check circulation? You need to look in your workshop manual under cooling system at the circulation system then use your hand to follow the pipes and hoses etc to find where the coolant is geting blocked.