I have a lanair mx300 (2018) bought it used. I took the preheater assemblies apart cleaned them in the parts washer, replaced all o-rings and seals, springs. I installed a draft damper in the exhaust using. I attempted to measure draft with a meter but Im either not doing it correctly or there's zero draft. I suspect lack of draft or back draft to be my issue. the top f the exhaust vent is only about 18" above my roof and my shop has a massive exhaust fan that is half a$$ covered with plastic at the moment.
The problems:
1. the flame is over firing, I do not have a tight compact flame but rather a more wide spread flame that is hitting the target board
2. the flame appears to be creeping out the inspection door at times. (back draft suspected)
3. when the inspection door opens item #2 ceases
4. smoke escaping from all seams; inspection door, chimney tubing etc. smoke exiting top of building is dark black.
What am I missing if anything, how do I correct it? Taller exterior stack? seal up exhaust fan completely?
