Is it still under warranty? Fitbit will probably just send you a new one at no cost. When my fiance's stopped reading her heartbeat, they shipped it quickly and didn't even ask for the old one back.
Hello! I had a similar issue with my Samsung microwave last year, except that blower and turntable would activate when the door was closed. I took it apart to find that the door close switch had become loose and moved. It seemed that it wasn't correctly detecting the door. Tightening the switch fixed the problem, but it still confuses me why the door switch would have any barring on the blower and turntable. Best of luck!