why does my electric shower get hotter each time its used?

Hi! Dave,
You are probably new to electric showers, but I'm afraid this is the way most electric showers function.
As the temperature outside get higher so you have to turn down the heat setting on the heater, this will be almost at setting 1 if the outside temperature is about 68 to 75 degrees F. Or change to what some heaters call Summer setting (mine calls it economy) which is not the same pressure at the shower head as the full setting as you have found out, I have the same problem but have used electric showers for som 40 years and they all do the same, the temp. outside at the moment (October) is about 58F so you must be setting your control to about 3 or 4. which would be about normal. I like a coolish shower so yours can be up or down to this
Hope this helps
Stan

Stanley
October 2004