I lit the water heater for the first time in my new TT and it seemed to be working fine. 30 minutes later when I went to turn it off, there was black smoke coming out of the vent and a bunch of soot on the side of my trailer. The soot wiped right off, no damage (whew!).
About a week later I lit it again and left it on for the same amount of time and there was no smoke. The first time I had the heater up full blast, the second time I turned it down a little.
After unit has been sitting (unused) for a while it is a good idea to inspect the water heater burner assembly to make sure insects haven't taken up residence in the burner venturi. Very common occurrence. It is possible you had a small nest or web and it cleared itself after that first use. But it is a good idea to check for a good flame and proper operation for a minute or two when you first fire up the heater after it has been sitting. I carry a small bottle brush that I run through my Atwood's burner tube to make sure it is clean before I set out on my adventures. Often it comes back out with spider web material on it!
Also when I first installed my Atwood (replacing original Girard tankless WH) the air shutter was not adjusted properly and the flame was way too rich creating soot. A quick adjustment of the shutter cured my mixture problem and it has been fine since. But since you were smokey once and better later, I'm leaning more towards a temporary burner obstruction.
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Rob R.
Akron, OH
2014 Seneca 37TS
Toads: 2019 Ford Edge ST or 2013 Ford Focus ST
Happened to me too once on my TT and again on a gas smoker. As Robbbyr stated, you need to clean the venturi. In both instances, spiders had build a web and the gas was burning incorrectly causing the soot.
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