Heater Problem - Black Smoke

[waste]

I'm pretty sure these are like the Max-E-Therm heaters by Sta - Rite, both of the above suggestions are reasons for this but think that gottliebo's answer is more likely. I've seen many heaters where mice have found their way into the ignition chamber and nested . However, if the unit has fired and sustained ignition a few times for a while, eventually the nesting materials would be fully consumed, as would the nesters So perhaps there is an issue with the air/ gas mix

[CarlD]

And here I was thinking: Maybe get some marshmallows?

(sorry, couldn't resist! )