Hotpoint WMA40 not draining?

The drum does not drain after wash, so rinse water goes in on top until it fills right up and overflows! There is NOTHING WRONG WITH THE PUMP: if you turn the dial to Stop and press the start button, the pump operates for 20 seconds, and you can keep doing that until the machine is empty. Is there a water level sensor which is kaput? If you turn it on to spin it will happily spin full of water. Or is it the timer/programmer?