Zanussi double oven:main oven temperature too hot?

I have a Zanussi double oven, the main oven has slowly been getting worse. It seems to be heating hotter than i set it. Well today it has totaly broke and not no matter what i set the nob to, the temperature is really, really hot. my top oven is fine.I've seen questions and answers about how to fix the element, but i'm asuming it's my temperature guage that has broken. Where do i find the thermostat and how do i fix it.
I'd be grateful for any help. Thanks