From the bloggers at Everything About RVing.
We started the hot water heater, it started fine but there’s black smoke coming out of the heater from the outside vent. It ran fine until it shut off cause the water was hot and it went out it did start back up when we turned the switch on again.
Since you don’t tell me the year, make or model of your RV nor the make or model of your RV’s water heater, I am going to explain things in general terms about RV Water Heaters. First and foremost, the fact that you are seeing black smoke coming out of the water heater compartment is not normal and you should not try to run the water heater again until this problem is resolved.
The most common causes of the smoke in an RV water heater can be something as simple as a spider or other insect nest in the burner tube or burner chamber of your RV’s water heater, or even the water heater running at too rich of a setting. My initial suggestion is that based on some of the questions you have asked me, that you take your RV in and have a Certified RV Technician inspect and repair the water heater.
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