OK. This is what I do: select 4D (fan oven), default is 160 C, start. After a few minutes (3-5) it beeps the error. It has got nowhere near up to temperature (there is an indicator line on the display). The top fan did not run.
To cancel the error I pressed the off button so the unit stops. After a few seconds it flashes up the message “unit cooling down” and the top fan briefly runs for about 5 seconds or so. After that the unit goes off.
It therefore seems to me that the top fan is functional and something else is going on. Does this help?