This only occurs rarely…. when the oven is hot.
I set the fan oven to 200 degC.
Everything works, until it gets hot.
But some time later, the temperature has set its-self back to 160.
The cooling fan is working OK
The over-temperature cut-out measures zero-ohms (when cold).
I realise this is an old thread but have a similar problem on a Neff oven. Did you find the cause. Customer had bought a new thermister which i fitted for her but still intermittantly resets to 160 deg.