I was called out on a Montigo Gas Fireplace Model B34DT 2 Serial #2-40825-128391. This equipment had been installed for several years and recently began having the pilot and main burner shut off together after the main burner had been on for 10-30 minutes or so.
This fireplace pilot was one of those with a clip on burner head that allows the pilot orifice to be removed for cleaning with an allen wrench (who's manufactures that, anyway?).
The pilot flame seemed a little smaller than I would have liked, but cleaning the pilot orifice did no good. The pilot gas was turned to max out the size of the pilot flame.
With the main burner off, the piloit flame decently engulfed the thermocouple, and there was no problem withy pilot outages.
Shortly after the main burner was turned on, some turbulence would be observed around the main burner flame, and the pilot flame would tend to be sucked towards the main burner. The thermocouple would no longer be adequately engulfed, causing the pilot outages.
This direct vent fireplace was top vented to the edge of a three story house on a long, fairly steep hill. Careful review of the installation standards disclosed no objections to this kind of installation.
So what was causing the turbulance, and how do you correct it? What additional information might you want or need to diagnose the problem, and where would you get it?