Unsure about your technical difficulties, especially considering all you did was clean the shower head and gasket, very weird.
In regards to the PID, I think the original Minore IIIs shipped with Minore II manuals, in which there is a set button for the temperature controller. For the Minore III, simply hold the left arrow for around 3 seconds until the temperature starts flashing. Then use the arrows to adjust accordingly.
Good luck with the issues