Hi SandervG and avogra!
Thank you very much!
At our university we use an ultimaker 2+ without any problems. I was so intrested in 3D printing I build a 3D printer by my own. Kinda like the Prusa I3.
I'm printing on a plain glass with some tape on for a better surface. But i don't know or it's helping.
I have to say that the room, where i'm printing in, is under the roof and kinda warm (25°C). When i'm printing I try to close the windows and doors so there is no ventilation in the room.
Maybe I can start again with calibrating the distance between the nozzle and the glass.