water temperate

The things to check first are.

1 That the main valve coming into your house is fully open.

2 Then check that the valve on the line to the shower is fully open.

If these valves are not fully open then there may not be enough water
getting to your shower to open / close thesafety device that allows power through to the elements

If the valves are OK then it may be an element failing whenit heats up, so when the shower starts to cool check the element forresistance..... See below.

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.

This Video may help

 http://www.youtube.com/watch?v=wzPt1hsfVq4cv

If you don’t have amultimeter  we sell them at around £10 each with a link to an on line guideon how to use them for checking 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 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