It maybe a faulty element in the heating tank (there are two, three in most 10kwshowers) you can check them with a multi meter you should have a reading ofaround 12>18 ohms.
If you have power to the elementsand 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 fix yourshower, 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 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-Testerhttp://www.showerdoc.com/trito-84500410-triton-heater-can-assembly---8-5kw-84500410http://www.showerdoc.com/trito-84500420-triton-heater-can-assembly---9-5kw-84500420
Not a direct swap, but the T80z should make replacing this fairly easy.
Remember to check you have the same kw rating