We also had a quadrafire 7100 installed in Nov 2012 and are experiencing the same problems using the automatic control. We are using the manual override all the time. We were also considering replacing the snap disk, we were wondering if a
snap disk triggered by a lower temperature would let it operate like it should. When they installed the second snap disk, was it the exact same one? Or did you try one with a lower setting. (I have been told you can purchase different settings)

I will be interested in more comments on this issue.

We purchased a 7100 in Oct 2012. After 2 months of flawless operation, the fans too quit working all the time. Fireplace Warehouse in Denver sent 2 people up, changed numerous snap discs and it still does not work. I have called the Corp office, poor customer service-6:23 minutes on hold the first time only to be hung up on being transferred to a different unit. 17:46 minutes the second time only to have a recording come on stating the office is now closed. Supposedly, the new area factory rep will call me tomorrow(8/9) and let me know when they will attempt to repair this unit. He stated that the field technician has retired and they no longer have someone available. Again, what great service!