Problem with Electric Shower
 

I have recently had installed a Gainsborough Electric Shower, with a push
button to start and stop the water flow. After around 10 days the push
button simply failed. I have taken off the cover and the relevant parts
inside consist of a spring push from the button, which appears to activate a
vertical spring-controlled on-off device. These are connected via a plastic
component which turns back and forth and is itself controlled by something
similar to a split pin. As far as I can see it is this 'split pin thing'
that has come adrift. I have tried to put it back but am not sure where
exactly it should lodge. Does anyone have any idea of what I'm getting at?
I've tried contacting the company but have had no response so far.