Hi, Occassionally we get the odd fume/smell from our of7 rayburn. A few months ago the flue got sooted up around the square fluebox on the top of the rayburn. No blockage further up the flue. We have no cleaning window on the flue pipe above the Rayburn. We do get odd bits of black debris around the air intake of the flue pipe. Is this normal? Does it indicate its a sooty flame? Any ideas.