I was sitting on the couch reading hearth.com forms and I noticed the secondary's where firing pretty heavy but was to lazy to get up and check the temp. By the time I convinced myself I needed to get up and check the thermometer was pegged. It was hot enough to make the air wash glow. Turned the fan on and it settled down to 700. I don't panic anymore. It usually happens a handful of times each year. What worries me is how many times it happens that I don't know about