Hi Momo,
finally some progress from my side 
The thing is that some surfaces where not properly detected due to the mesh and you also did not add a part that needs to be cooled which does make much sense for this type of simulation otherwise we could just have used an incompressible simulation type. In the picture below you can see the added Power Source with 20W (just for testing purposes) and changed the boundary conditions as you can see in the tree. Worked like a charm!
If you want you can try it out by yourself and let me know if you have any problems with the setup.
Best,
Jousef