Getting back to the 755/3 breakdowns, the section between Bury and Chippenham seems to be the most popular point of failure, so either the gradients are an issue - or it is a software glitch, or maybe the cooling system on the 3-cars is less up to the job than the 4-cars. Either way there are some very well paid Stadler and Deutz engineers out there whose job it is to sort the issues out!
Thankfully failures on my travels have been rare.
What does seem to be an issue is the fact there does not seem to be any early warning of an overheat situation. Once the alarms start going off, i understand the trains starts going through its engine shutdown procedure, and cannot be restarted until that has happened. The whole shutdown rebooting i am told takes around 15 minutes. Operationally that seems crazy. Surely there should be some early warning of rising temperatures so that drivers - a la class 800's - can ease off the power or take some measures to allow the train to cool down, rather than experiencing the sort of shutdown PC users experience when their PC decides to update and restart without any warning!