Sucking air

I have an all-in-one pump/filter/fountain. Recently it has started falling
over and on one occasion it rose completely out of the pond! There's lots
of air in the pump when I stand it upright.

I don't know why it's started doing this (it's just a year old). I think it
might be to do with hair algea getting caught around the vents and perhaps
the pump is sucking the air from the algea?

Any ideas?

Cheers,

Steve