Flow problems with Watermill wasp 66 shower pump

[manorgirl]

Hi Can anyone help.

I have a Watermill wasp 66 shower pump which has been running great for 4 years.
For the last few days it will only run when shower valve is opened slowly and then gradually opened fully.

Any advice would be great

Thanks

 

[Ermintrude]

Sensor on its way out I'm afraid