I found this on the website... page 49 of the instruction manual
Automatic shut-down
Blocking and run-dry protection with alert
sound:
When the pump is blocked, an alert sound
(continuous sound) is released by the driver
(2), at the same time the pump is switched off.
After the blockage has been removed, the
pump is started again automatically after a
delay of 20 seconds. When the pump runs dry,
another alert sound (beep tone) is released,
the pump continues to run at low protective
speed. When the pump draws water again, the
beep tone will go off.
Warning ! This warning sound is not audible
when the Wavecontroller is used. Nonetheless,
there is no danger of overload in case of
complete blockage as the driver operates at 50
per cent of the performance possible on
account of the Wavecontroller.