All - can anyone give me any advice?

Hoover AL130 washing machine about 4 years old. This is what it does
(from empty):
Fills OK
Turns backwards and forwards as expected
Keeps on turning back and forth ad infinitum.
If you set it to a spin cycle, it spins OK as long as the drum is
empty..

It has a manual rotary controller which doesn't move from the position
you set it to.

It doesn't seem to be even attempting to empty, so I suspect it's not
the pump. It doesn't seem to get that far.

The problem occurs the same regardless of the temperature the machine
is set to, so I don't _think_ the problem is with the heater element.

Does it sound like the controller that's gone wrong? Or something on
the control PCB? Or could this be a symptom of anything else? Is it
worth trying to take the controller apart and service it, or should I
just buy a a new one (they're quite expensive)?

In an electronic engineer so I'm happy testing, taking things apart
etc. I just don't know much about how these things work.

Any other ideas?

Thanks for any help in advance!

Jon.