Triton Opal Service?

The temperature and flow rate are always (Nearly always!! and always in your type of shower) connected.

When you turn your shower on you have a 7.5kw, 8.5kw, 9.5kw or 10.5kw element heating the water and this does not vary. The way you alter the temperature is by varying the amount of water that passes over the element, pass the water over the element slowly (a little water) and it gets very hot, pass it over quickly (a high flow rate) and it doesn’t have time to pick up much heat.

This explains why in the winter at the same setting as the summer the shower is not so hot because the temperature of the incoming water has changed.   

However if the shower is uncomfortably cool then you may have a faulty element, see below for how to check.

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.

http://www.youtube.com/watch?v=wzPt1hsfVq4

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.showerdoc.com/installation/electrical-products/SKYTRO-600-005-Digital-Multi-Tester