Headgasket, timing chain/set, valve train all new in Oct. I was thinking maybe headgasket failure also, but nothing else points to that...no loss of coolant, no water in oil etc. Yep, plan on heater core flush this weekend, but if it were clogged, wouldnt I never get heat?

This morning on my way into work, no heat and this: I heard a little 'click' behind the middle of the dash and WA-LA, HEAT!! Is there a vacuum pod or something back there that would not be opening/closing properly?