Mainboard fan not running

I was just wondering if the mainboard fan on the SV06 Plus is always (?) turned off, or under what condition it will turn on. Checked today with an IR camera to see if there are irregularities and well - one of the stepper drivers was at 90 °C and the fan still turned off. Is this normal? Shouldn’t the fan be on to prevent this?

Checked if the fan was free to spin and didn’t find any problems. All other fans are working as should be.

Edit: For som reason unknown to me, it just turned on. So 90 °C on the drivers appears to be considered safe I guess? Now the modules are below 55 °C.