Our (very old) electric shower is leaking. It seems to be where the cold water goes into the unit. Rest of the water heats as usual and shower seems to run fine, but lots of cold water is running down and flipping freezing.
electric showers are throw-away items. Buy a new one. The size of the electrical cable will determine the maximum power you can have. An electrician will easily identify it but will need to see if the cable passes through insulation.