Lower Radiator pipe came off

[shailesh]

Hi, was driving today and 2 kms just before my house the lower Radiator pipe came off. Car gave a warning of low water in radiator. 


I replaced the lower pipe again as it seems the clamp on the pipe came loose.,filled it with water did the bleeding process and went for a drive.
All seems fine. I  will drain it again and fill anti freeze. 

What could have to cause the pipe to pop off? 

E60
530d

 

[sash]

The only thing i can think of is that the circlip thingy got stretched, but that would imply multiple removal and fitting back or damage to the clip while removing.