Surfacebook 2 gets hot in standby

I already got a new Surfacebook because my old one just didnt start one morning but is was hot as hell. Microsoft took four weeks to send me a nother broken unit and another five weeks to send me a working unit.

But for a few weeks I noted that sometimes the screen dosnt turn off when I close the computer and that the whole unit heats up a lot. that also happens often when the screen turns off and I close the Surfacebook. It also happend that I put the laptop in standby and don't connect it to a power source. It should turn off completly after 30 minutes but the next morning the laptop is hot but the batteries are low or empty.

I ran the Diagnostic Toolkit but it didn't find any problems. I also started the Laptop with a Clean Boot and there is not programm using a lot of the CPU, GPU or RAM.

What can I do without sending the Laptop agen to Microsoft. I need the Laptop for university and can't go another semester without one.