Re: Smeg UK80MFX Thermostat stays on when in off position.
It does sound like a typical thermostat failure, the one required is this one if that’s the fault. The only other thing I can think on that would cause that is the changeover switch which controls the oven functions but, even at that, I’d still be very suspect of the oven thermostat.
There is no adjustment on the thermostat that will solve a problem like that. If oven thermostats are adjustable at all, it’s only to allow them to be calibrated within a few degrees.
The safety stat, which I think is this one but I’d need the full model number to check fully, only cuts the oven power if it overheats. So it’ll get to about 275?C then just kill the power to the element until the oven cools off.
HTH
K.