why is ringer turning it self off?

[the whole taco]

Go to Audio settings, when facing the equalizer swipe to the right and scroll to the bottom, you find an option there that the phone mutes when facedown. I had trouble too with Windows Phone's in my pocket face down and not ringing.

good tip
but I know that isn't the issue with mine as I tested it with the phone facing up to check it was "ringing" with no sound.

 

[R Gilbert3]

After nearly 3 weeks of behaving itself, it did it again this morning......