We have the 10.8kw Mira Sport. Had same problem and got it repaired twice under warranty both times new PCB Assembly. Apparently Mira have improved the design of this at least once following troubles with showers dieing caused by ‘spikes’ in the electricity supply.
There are good instructions for replacing the PCB Assembly in the handbook that should have come with the shower. There is a pdf file of the manual on this site: http://www.tradecounter.com/dbdocs/mirasport10-8.pdf_tcc_13-02-04.pdf
Alan
January 2007