Thanks, but, i have checked and i don't have air in the system.
It's embarassing cause i use my computer everyday for a professionnal use, with a big utilisation of my CPU (for render).
But before this trouble i was very satisfied with this model.
I have checked during a big and long render, the CPU temp is good so the pump work but i don't know this piece can be break in few days or weeks.
So i think the best thing to do for me is to return this model, but how much time it will take to give a new one in replacement ?