Its not unheard of for relatively young F125 switches to fail - Neil's only did a few thousand miles before it needed replacing. Did it go in to limp as soon as you selected 'D' or did it wait until you moved? Does it reverse ok?
VCDS will tell all
Btw, I wouldn't be at all surprised at it running a little hot in this weather while it's in limp mode since its stuck in 3rd gear.