For what it's worth. My 2013 Volt has occasionally had the no heat problem when calling for cabin heat. Long time ago I took it to the dealer who said they had to reset the computer. What I started doing and it has worked every time when this happens (which is not often), I pull the F5 fuse (HVAC) on the left fuse panel of the dash and wait about 1/2 minute and plug back in. My Volt has just turned over 100k miles. Not sure if their is another fix, but this works for me.