Simpson Eziset 800 won`t stop filling with water?

Hi there,
My simpson Eziset 800 won`t stop filling with water regardless of where the level is set.
I have blown out the hose to the level unit, tested switch unit and found it to be in a normally closed position then i gently blow into the hose with other end connected to switch hear it click and it goes into a normally open position. Hose doesn`t appear to be leaking.
Any idea`s?

Kris
August 2010