Hello I need some advice/help. We have a magnum stoker coal stove. We lit it up for the first time this season and all was well and working great. Went to light it up again and the feeder and combustion fan lights were blinking like crazy. We cleaned it out really well after doing some reading that buildup is main combustion issue. Went to light it again and lights stopped blinking, great except we got a sulphur smell which seemed to be from fumes coming back into the house. Chimney has been inspected and is fine. Advice please? We would like to be warm lol also coal is not wet and is the proper type of coal