this shower has a built in temperature sensor its a safety feature which will cut the shower off if it believes it is too hot follow the reset instructions in the guide basically have the water at its lowest temperature to start with and gradually raise it up you can find all you need to know here
http://help.tradingdepot.co.uk/wp-content/uploads/2013/09/mira-advance-9kw-user.pdf
andy
February 2014