Caple CR903SS cut out thermostat

Hi there, looking for some advice on a problem with our cooker, have looked through the topics but can’t quite find one that matches.

We have a Caple CR903SS which has two ovens/grills side by side. The bottom element went in the larger oven. Not obvious for how to access this, but after taking the back off and finding a ‘false floor’ worked out to get to it. I hadn’t touched any of the wiring at this point, but upon reassembly the large oven wouldn’t work any more (no power even to the light). The power to the small oven and clock was fine.
Replaced the bottom element today and had a good look round the rest of the wiring and everything seems to point to a cut out thermostat (Delonghi PX906, which I’ve identified by looking at spares pictures) on the back as the main power leads go through it including the oven light and there is a slight charring of the plastic terminal covers.

http://www.4caple.co.uk/cgi-bin/product.pl?PID=429731

So after a rambling intro:
What does the cut-out thermostat do exactly? If it is a thermal ‘fuse’ then it would make sense. I tend to think of thermostats being able to cut on and off many times. As it is a cheap part I’ll probably order one any way.

Secondly, What would likely to cause it to go? Do they fail often?
As I only touched the bottom element, the only thought I had was that I moved it in such a way that it made an intermittent circuit which overloaded the thermostat. (May be completely implausible!), but if there is anything else obvious to check or replace at the same time please let me know.

Thank you in advance for any guidance.
Stuart