Clip not done up properly. The system should pressurise any way but not enough to blow a properly fitted hose off.

 

Clip was on the same place as it always used to be . Perhaps it's not giving enough pressure any more .

 

There's a couple of possibilities.
I assume you checked the connection on the radiator is still in good shape, with the edge to hold the hose?
Clips can stretch, easy to replace with a proper hose clamp. The hose itself can expand, so you need a bit more force to clamp it into place.
I'd also check the pressure after the engine has run up to temperature. It should be pressurized but not rock hard. If it is, check the cap on the expansion tank. If the tank was overfilled and can not vent, pressure can rise and something will give.
Fingers crossed it's not the engine building pressure...

Filip

PS: where in Belgium are you from? Rare to see a countryman on this forum. ;-)

 

Thx for the reply , it's strange I had it 3 weeks ago and then nothing since a few days ago ...
I also hear a ratling noise sometimes. I live in Kapellen , north of Antwerp and where are yoy from?