I have the same problem. Water flow excellent (unchanged) - flow is too good to suggest that it is the head that needs descaling. Overheat comes on when Medium or High setting.
Power cable to the unit is a big fat cable ... cooker size. Not a problem of power as it has worked for years too.
I have a Mira Sport Max which has been installed and working for some time. I now have a problem where the overheat light comes on whenever the power is set to medium or high. The water pressure is strong and flows well (not changed). I just do not get any hot water. Does anybody have any...