Larry,
It's one of the self-contained showers which heats the water as it passes through the unit. You just have a cold supply which goes via a control valve, then to the heating elements and straight out of the hose. Temperature adjustment is made by regulating the flow with the valve (i.e. slower rate of flow results in hotter water).
The heating elements on these do not normally cycle on and off during operation, unless reduced pressure or a restriction on the outlet causes the water to get so hot that the safety 'stat on the output opens.
Here's the actual model in question:
http://www.shower-spares.co.uk/triton/tx7000i_and_tx7500i.htm
