[urq] general overheating question

[Keith]

Evening All

Apologies for this being a bit off (urq) topic but I could really do with a bit of general diagnostic help with an overheating issue on our Audi A6 1.8t (2001). 
The symptoms are:
Sudden overheating issue.
No steam
No bursts
The coolant level had dropped a little but there were no obvious leaks although there was some coolant on the lip of the coolant reservoir suggesting that this might have blown out past cap through overheating. The low coolant level alarm sounded when this all occurred which drew my attention to the temp gauge. Got towed home to hopefully now fix it.
The oil seemed to have got hotter than normal too.
Bought new filler cap to rule this out.
Then.....
Starting from cold, it rises very quickly to 90c (normal operating temp), hangs there for a bit and then goes on rising.
Viscous fan and electric fan both working fine and when they are supposed to.
Heater just blows cold air even when overheating.
Whipped plugs out – all normal colour.
Tops of pistons look normal – no evidence of steam washing.
No obvious evidence of oil in water or water in oil.
Engine starts fine and runs as smooth as normal.
Thermostat is less than 12 months old. Changed when previously car was not getting warm!

My two main suspects are thermostat despite it being almost new and water pump. 
Have I overlooked anything simple and blindingly obvious?
Before I start taking it all apart though, what can I do to narrow this down to the the definite culprit? 
I really need to fix this by Monday when I have to use it for work (no pressure eh?) so any suggestions of next steps will be greatly appreciated (as always).
Cheers folks. Will look forward to hearing from you.

Keith
‘87 WR