Thank you for the video! Seeing a 6A without a choke (the venturi appears intact), then it will run a minute or two, then there's a little "chuff!", the flame goes out and I see a 6L. I cleaned it recently, including the condensate bottle. It remains to check the drain pipe. One wild thought is the supply flex-pipe may be undersized and its auto-shutoff might be partially triggering? Except I would expect one of those to be snap-action and latch on.
Sniffed around after smelling a bit of propane, used a flashlight to look into the gap between the blower motor and blower body and saw that the blower shaft seal had popped out! Leak and airflow disturbance explained. Hopefully I can push it back in, maybe add something to keep it in place so I won't have to replace the $600? blower because an under-$1-to-manufacture seal popped out. Still going to replace it with a heat pump, but now it's a less urgent situation.
