I have noticed lately, that my main fan oven tends to overcook food, even burning and ruining the food, when I have followed cooking instructions to the letter.
I have checked the oven settings by using a food oven probe, set at the same setting as the oven. However, when the oven reaches the set temperature and the probe reaches that temperature, the probe beeps, but, THE OVEN KEEPS ON HEATING UP and the probe Temp rises until the oven red light goes out. The probe shows the Temp as up to 188c when the oven has been set at 150c. Other temp. checks are as follows. Oven set at 180c, probe shows 200c. Set at 200c probe shows 216c and oven set at 220c, probe shows 228c. CAN THE HEATING CONTROLS BE CALIBRATED SO THAT THE OVEN STOPS HEATING WHEN THE SET TEMPERATURE IS REACHED? If so, HOW CAN IT BE DONE AND WILL I BE ABLE TO PERFORM THIS TASK? I have NOT checked the temperatures on the TOP oven, just the main fan assisted oven.

grg storey, March 2020

I would suggest that the main oven temperature sensor has failed and would require replacing with a new part. It's a fairly cheap part that's commonly available and not too difficult to swap out.

Rupert, March 2020