Regarding red ring model 5005 expression ?

Have a problem with the shower heating the water after it's been switched on , I'm getting a little heat with it turned to max on high but if you run it for 20 minutes it will eventually run hot , was a new board fitted to it 2 years ago when under warranty , if you'd any ideas what the problem is I'd appreciate it ps red ring Tec have said possibly micros switchs need replaced ?

Mark
February 2017