Little bit more progress on the cheap TDi (although at the rate we're going, that's not going to be a long lasting name).
1) Fitted temp sender (Febi Bilstein) in hope of seeing some temp gauge action after new thermostat saw no difference. It was to no avail: gauge stuck on 60, so will fish out VCDS over weekend to see what readings the cluster and the ECU can see. Odd for two senders not to produce a reading: wiring?
2) Got the heater fan working. Started by removing it, adding oil and attempting to run it up. The odd fitful rotation and that was that. I managed to remove the motor from the housing which gave slightly better access. Turned out that one of the brushes was barely making contact with the commutator. Try as I might, I couldn't quite get it to work without external assistance. In the end I used a couple of small blue elastic bands (non conductive you see) to gently assist the brush into position. OK not a ten year fix, but it's back in, working perfectly, cost nothing and proves the rest of the climate control is working fine.
3) Sorted the phantom open boot for now: it was the wiper that should activate the microswitch in the boot latch mech. It was worn just enough to fail to operate the switch. For now I managed to melt a bit of plastic (from a trim clip), applied via hot screwdriver, onto the wiper and amazingly it's working. My backup plan was to simply leave the latch disconnected which would leave me with all functions but bootlight. Anyway, like the fan above, it proves everything else is fine and I'll pick up a good latch when I see one.
4) With above sorted, no dash warnings so celebrated by activating mini-DIS. Car said thank you by producing appalling initial economy reading this evening. I suspect that takes me back to the temp sensor issue.
5) Started to muck the car out: outside is quite presentable now, inside not so much, so did first couple of hours of basic cleaning. Lots more to follow.
It's off on something of a maiden voyage tomorrow as I'm working 70 miles away fitting an E-Type bonnet, so will risk any temp reading issues and let it absorb some of the Esso premium diesel as a semi Italian tune up.