You might want to try setting it for high altitude (or vice versa). There's a sequence you do after grounding out a pin on the harness near the heater. F02 is normally thrown when there's air in the line. It's quite possible that the heater is set for a different altitude than you've been operating at. That could explain a cold vs warm issue. Also, I'd triple check your fittings and make sure there are no air leaks on the intake or exhaust. Might also behoove you to remove the intake and exhaust silencers and see if that returns it to proper form.
The fact that you can get it to fire after draining the line and then reconnecting sure sounds like an air bubble related issue to me. I have F02 semi-often because I made the mistake of using a ~6" section of 5/16" line right out of the tank before stepping it down to the small diameter webasto line. I'm 99% sure that due to the large fuel line diameter and the step down that an air bubble/empty line issue forms there which has to purge if I don't run it regularly and the line drains back into an emptyish tank. Usually 2-3 restarts clears it and all is good. I did have an issue during my recent California trip where the heater would run for 30 minutes and then fizzle out. Consistently. I was worried about the burner being plugged up or something, but it turned out to be a tank of gas that the heater didn't like. Old gas station in Garberville. Maybe some water, or fuel that was over winterized. After running the tank down and filling fresh it worked like a champ for the rest of the trip.
Lastly, you ended up using the aux port on the fuel tank, yeah? If so, make sure that you have half a tank or more of fuel. Below that you'll be sucking air as the aux port doesn't run to very low in the tank.
Hope you get it figured.