power/electric/mains/auxillary pump shower. what's the difference?
The instantaneous electric shower is connected directly to the incoming "mains" (city water) supply, and heats the water on demand as it passes through the unit. It has the advantage that you're only paying to heat water that you actually use for as long as the shower is running (although if you already have a cylinder full of hot water for the rest of the house, that might not be of great importance anyway).
The main disadvantage is that because the water is heated as it passes through the unit, the output temperature depends upon the rate of flow and the temperature of the cold water entering. In other words, you have to reduce the rate of flow in order to raise the temperature. If you like hot, forceful showers, you might be disappointed with the results. The electric shower also needs its own dedicated electrical circuit (if you already have one, be aware that it might not be sufficient if you upgrade to a higher-powered shower).
The basic mixer shower (with no electrical involvement) takes water from both hot and cold storage tanks/cisterns. If you have the traditional British plumbing arrangement with a cold cistern in the attic, these will be at the same relatively low pressure, since gravity is the only force behind them. Pressure can depend very much upon the head of water available. If the storage cistern in the roof space is only a couple of feet above the shower head, the pressure can be quite low.
This is where the pumped shower enters the picture. It still takes both hot and cold water from your tanks, but adds an electric pump to increase the pressure and flow rate. If you like a hot shower with some force behind it, you'll find this option generally gives far superior results to the instant electric showers. There are pumped showers which come in a wall-mount box which from the outside looks exactly like the instant electric shower, but it's also possible to fit an auxiliary pump under the bathtub or in an adjoining cupboard and then you just have the controls and shower outlet visible, just like any other regular mixer shower.
[Edit] Unlike the instant electric shower which needs its own circuit, the power requirements for a pumped shower are minimal and can usually be obtained by connecting into a convenient nearby circuit.
[/Edit]"Power shower" can be a confusing term. It's most often used to refer to a pumped shower, but some people/manufacturers also use it to mean an instant electric shower.
the back of the shower backs onto the insdie of the airing cupbard where the water tank is. if that helps...
That would certainly make the plumbing job easier. Before you plan anything further, check what type of cold supply you have. Is it direct from the city water supply, or does it come from the cold cistern in the attic?
