The settings on the shower set only the level of the heating element, not directly the temperature of the water. One dial sets the element at it's temperature, then another dial normally setts the flow of water across the elements. The faster the water flows across, the less it will be heated.
If you feel the shower is not hot enough for your liking you must first look at the flow rate and reduce it, this will make the water warmer. Secondly look at the temperature of teh water going into the shower. If the water is coming from a tank that is frozen cold the shower will not be able to heat it to as high a temperature as if the incoming water were warmer. Check this and consider lining, moving or adjusting the inlet water.
If you feel the heating element is not heating up, get this checked.
If your element is heating up, the flow is OK, and the incoming water is not particularly cold, you may have to face up to having bought a less powerful shower than you require. Only a more powerful heating element (9.5kW, 105kW etc) will get your water hotter.
Rabutha Conundrum
February 2010