It may be a faulty elementin the heating tank (there are two, three in most 10kw showers) you can checkthem with a multi meter you should have a reading of around 12>18 ohms.
If you have power to theelements and no heat it's probably the elements, no power to the elements thenit's probably a micro switch.
If you don’t have amultimeter we sell them at £10 each with a guide on how to use them forchecking and testing the various parts of your shower.
Apart from helping to fixyour shower, they are really useful for checking you have a power supply toappliances, for checking fuses, letting you know much power you have left inbatteries
(so you know if they are dud ornot) and lots of other jobs, in short they are well worth the £10.
http://www.showerdoc.com/installation/electrical-products/SKYTRO-600-005-Digital-Multi-Tester