Hi folks, just thought i could add to this thread.
As per my other post about the resistor+wiring melting on the heater, couldnt believe it this morning when on way to dealer for said repair the radio went dead !!
Little bit of research throws up cold seems to be the problem, also it seems it causes the temp and clock to stay on when you get out and lock the car.
Anyway in my case and as others have said temp fix seems to be disconnect power to the radio for a few mins, i also warmed mine up with a hairdryer ! re-connect, enter code and it's all fixed.Including the temp and time now going off correctly.
Why the two are linked i do not know, but i know when i disconnected the yellow plug from back of radio, which i assume is the display/remote control wire the temp/time went off, they do share the same piece of display ?
I think in my case perhaps having no heater working in the car since Xmas eve may have made the problem occur combined with -5 degrees this morning.
Did the hairdryer help ? dunno, but if it goes again i'll be doing both steps.
Hope this helps