Bosch oven – HBG6764B6B/63 – switches itself off after 5 mins or thereabouts

Customer says the oven switches itself off. The oven is 4 years old according to the customer.

When I arrived, the oven seems to be behaving itself. I’m none the wiser. The oven maintained temperature throughout.

I admit that I am not overly familiar with this hi tech oven so I am trying to go over the basics such as checking all heating elements and temperature checks.

I do know of these type of ovens have multispeed circulation fan failure and this is superseded by one speed circulation fan but the fan seems to be doing ok.

any thoughts?