I have a Heatmor outside boiler and I have just started using coal and have slowly been getting the bugs ironed out. The new problem that I have run into is that when I open the door I get small explosions and horrible flash when the smallest amount of air is introduced during the shutdown cycle of the boiler. I get worried that I'm going to blow the thing up because it gives of a pretty noticable BOOM even when the blower kicks on.
Is it from a lack of draft to carry the gas out or is it something bigger??