Wind gusts on the roof causing back pressure in the flue. This would not depend on the physical location of the actual furnace. That is what I meant. It makes sense to me, and I say it is a bad design in that if the wind caused back pressure, and then the situation is resolved, it should not require manually reseting the furnace. If I was king, I would change it so that if the furnace is running for several hours in 3 blinks mode, it should reset itself.