aeg oven

have not seen this yet as its a few miles away
aeg SECP43NH prod 949718143/04 electronic single oven. customer says sets it to 180 gets up to temp then drops to 150 and has to reset to 180 she rang aeg who advised probably thermostat (sensor) I advised that it might be pcb or sensor but as I have yet to see one of these I have very limited knowledge.
anyone out there familiar with these?

thanks wilf