When I switch on the shower unit, the led lights for a fraction of a second and goes off, the led in the pull switch also goes off. I then switch off the unit and the led in the pull switch comes back on. I can repeat this numerous times, it doesn't trip out the mcb at the consumer unit.

Derm, September 2016

Check the pull switch it's likely that the wiring or the switch is burnt up ( please isolate at the mains first )

toptrish, September 2016