Oven – Turning on oven’s fan for preheating – Oven turning off by itself – How to preheat properly

Should I turn on my oven's convection fan for preheating? Or should I only turn it on when I put the cake inside?

Because my oven OFTEN turns off by itself when preheating, I think it might be the fan.

I have researched a lot about this, oven turning off on it's own means the lack of airflow or overheating, I preheat the oven at 180 Celsuis for 20 minutes with the fan turned on.

I'm asking this question because it happens often times. So trial and error doesn't really work here, if it did turn off all the times, I could try a lot of things to narrow down the problem. I have tried preheating without the fan and it still turned off again if memory serves me right. No I was wrong we never tried this, because mom persists to use fan all the time.

This is a gas oven with physical rotating knobs, and about a handful of times when I was about to put the cake inside, I found the oven turned off, the lights are on and the fan is on but the flame is off, and the oven is somewhat cold and if I turn it on, it works fine, I never found it turned off with food inside.

After reading your comments I feel like I'm not doing the preheating correctly.

I searched more and found a suggestion on the internet to preheat the oven 25 Celsius degrees above the required temperature to cook [source].(https://avivservicetoday.com/ovens/how-to-preheat-your-oven/) But I don't like this since my oven doesn't have digital temperature display, I might overheat it or even underheat, it could ruin the cake.

There's also another suggestion saying preheating longer than x minutes could automatically turn the oven off, but as I had read the manual of my oven before asking this question, such thing was not mentioned.

About the fan, the manual suggests to use it to cook the core of food efficiently. In spite of other ovens which suggest to use the fan for browning the tops.