Though the water level sensor "clicks" when you blow through it (and
incidentally, these
switches can be sensitive so blow *gently*), there is no guarantee that
the switch is
working behind this.
Power down the machine and either use a multimeter or some concoction
of lamp
and battery to prove that the switch is in fact changing over.

At a guess I'd say that the pressure switch isn't working leading to a
"water level low"
state hence the machine keeps admitting more water ad infinitum.

But then I've been wrong before...

Regards

Mungo