Quick update:
Vital signs reported 33C when I started (this may seem high to start but I had been playing with it on & off). After a few minutes it had reached 36C. An hour later and it still says 36C so it appears to have stabilised at this temp. It would usually have climbed fairly rapidly to around 47-48C. The next thing I want to do is rig up some kind of control circuit that turns the fan on & off with temperature.

Maybe there's some kind of hardware+software hack to enable Mark Lord's temp alarm to control it.