It may be a faulty element in the heating tank (there are two, three in most 10kw showers) you can check them with a multi meter you should have a reading of around 12>18 ohms.

If you have power to the elements and no heat it's probably the elements, no power to the elements then it's probably a micro switch.

If you don’t have a multimeter we sell them at £10 each with a guide on how to use them for checking and testing the various parts of your shower.

Apart from helping to fix your shower, they are really useful for checking you have a power supply to appliances, for checking fuses, letting you know much power you have left in batteries

(so you know if they are dud or not) and lots of other jobs, in short they are well worth the £10.

http://www.shower-warehouse.co.uk/erol.html#55x878

Click on the link below, choose the manufacturer of the shower you have, scroll down the list of parts and select the part number you require.

You can then purchase the items online or call the office on 0131 443 9917 pressing option # 1 for spares.