Just a thought might be no good to you, but who knows..??
I have for a few years been having trouble with one of my combis, Some times it would go for days or weeks ok, then out of the blue over heat for no reason at all, well not one I could find. Eventualy got real bad. While I was having this prob my tappets were hell noisy. The other week I sorted the problem.. suddenly the tappet have gone great nice and quiet and the engine ticks over better it is a diferent engine.???
I think it could have been cold or hot spots in the engine that made the tapets noisy, as I had to flush it as part of the overheating cure. Check you do not need to top up water now you have ran the engine.
Just a thought good luck Pete