how can i fix my aquatronic W8500 no water at all?

Most likely fault is that the solenoid coil is open circuit. This is the brown bobbin with two connectors attached to it's right hand side situated centrally in the base of the shower. When you turn on the shower 240v is applied to the coil which electro-magnetically lifts a valve and allows water to flow.
The answer is to purchase a replacement coil assembly, or if you have an old shower (or even a scrap washing machine) handy you may find a similar coil. It will need to be removed complete with it's metal housing but it 's only an interference fit held in place by the splayed central mount and should come off if you can pull it straight forward. DO MAKE SURE SUPPLY TO SHOWER IS ISOLATED BEFORE ATTEMPTING TO REMOVE COIL.

SICKOWL
March 2009

check the power connections between the switch and shower
they are prone to come loose.

hi-spec plumbing
July 2007