Rob R. wrote:That makes no sense at all, a chimney like that should draft exceptionally well. Is there plenty of fresh air available to the boiler room? Is there anything else tied into that chimney?
There is definitely something drastically wrong here.
I say it is the coal...or maybe stated another way...the ash content of the coal.
I have mentioned this earlier to NWB, ash may be such that it is smothering the idle fire in the fire-pot.
Even with better drafts, if the ash is choking out sufficient air/oxygen up through the fire-pot an out-fire will certainly occur.
My questioning his hopper lid integrity and other alternate undesirable air paths/sources was due to my reasoning that draft will always draw from the least resistive air source.
Perhaps most all the draft is simply coming in the port cover plate...thereby bypassing the hot coals in the fire-pot to the point of causing another out-fire.
I know NWB tried some other coal, but perhaps it needed a little longer time to get the ash laden coal purged completely off the grate to really see any real difference.