Shower not firing pump

[SpeedChimo]

Hi, wonder if any clever soul could offer some suggestions here please.

I have a 2017 T6 Ocean with factory shower. I can't get the shower to trigger the pump by flicking the small toggle switch. I've checked switch with a multi-meter and that that appears to be fine, also seems to have a live feed when I check the wires beind the switch. The pump does not run, no matter if I have the shower trigger handle pressed in or not. I'm not 100% sure if the pump should run when the trigger is pressed or if it should run continously when the toggle switch is used... anyone know? However, if I turn on the sink tap just enough to fire the pump and go round the back to try the shower, it works fine.

Any ideas? Driving me mad!

Gary