Josey wrote:
On an Indesit double oven, main oven is fine. Smaller oven was ok, but now
will not reach temperature.

You can set the dial to say 220, but the oven only gets to 100. If you flick
the dial back down to see where the indicator light switches off, it's
always at 100, no matter how long you leave it to heat up (and of course the
food is not cooking properly).

Any idea what might have failed? - I can see a thermocouple at the back of
the oven, or some kind of controller?

My first thing to do would be to make up a medium size block of ice, and
place on the thermocouple.

If it's not exceeding 100C, then either the controller is turning off
the heating element, or the heating element is broken.
Do you own and have a license for a multimeter?