I like to finish with an ice-cold shower but when I turn the mixer dial right down to 'blue' I get cold water for about 5 seconds then it becomes tepid, as if some sort of safety device has kicked in. Very occasionally it stays cold like I want it to be, but this is rare.
This issue does not happen with the water from the mixer tap in the sink in the same room.
You'll need to strip back to the basic works of the mixer tap. These vary with make. Yours is set so that it doesn't turn the hot supply fully off. You should be able to adjust the stops so you can get just cold. The downside is that the hottest setting will now be cooler.
tricity and water don't mix, though I was involved in the marketing and licensing of pulse power drilling (inc applications like dental drilling - that involved good voltages and plenty of cold water. Fun too, drilling through the sandstone block walls of the U. of Glasgow physics building.
I'd like to know the answer to this one too. I get woken in the night by really hot feet and the shower don't stay cold for long enough before it goes tepid.
I have the opposite problem in hotels - the shower is never hot enough because it's got some sort of infernal elf 'n'safety device fitted which limits the maximum temperature - I always emerge with goosebumps!