Mira Advance Electric Shower?

My Mira Advance electric shower does not work. When you pull the pole switch on (the isolator switch on your bathroom ceiling) the power light comes on in the switch.
However, no power light comes on the Mira shower unit. There is power to the transformer, and the manual press on the top of the pressure valve releases a torrent of water, so no filter blockages apparent. The service light does not come on either. Can anybody enlighten me please?