What is wrong with my Mira electric shower as it is staying hot all the time

The shower has a pressure switch that is stuck. It could be that the orifice leading to the diaphragm is stopped up which will cause it to stay on all the time. You need to take it apart and check the switch with a digital multimeter. Unplug the power from it until you fix it. This is an easy fix, but you may need a new switch, but I doubt it.