I want to replace an Electric shower with a Power shower in roof conversion en-suite. The cold water tank is at the same level and the HW Cylinder is on the floor below. Is there a unit that can be exchanged "like-for-like" i.e. rising cold main only or have I got to get a hot feed direct from the HWC. Final option is for a higher wattage electric shower, I suppose?!
A power or standard mixer shower requires a hot feed directly from the hot water cylinder and a cold feed directly from the cold header tank.
There are issues with feeds, heights and water levels that will effect the choice (or even if you can fit) a mixer shower. Choose a model and download the installation instructions from the net. They are almost all available. This will tell you how they will need to be plumbed.
You probably could upgrade the electric shower, but the feed cable is likely to need upgrading too.