If the main oven isnt heating then its usually either the heater itself, therostat, selector switch or thermal cut out at fault.
Theres also a thermal cut out on the side of the oven, When you pull the oven out remove the top and look down the inside besides the fan and theres a thermal cut out on the side there as well, Check them.
Also ive just uploaded the wiring diagram so click the link below and check that. Now it does go of the serial number so you need to check it. You need the first 3 digits of the serial number to work out which diagram you need.
Check that and see what you find and let me know.
No worries thats fine.
Hopefully with the diagram you can find the fault.
I see the question is still open. Do you still need help on this?
If not then if you could remember to rate the answer that would be great.