Gas fireplace vent

Inspected a 2003 built home Sunday and gas fire place over time has discolored soffit and gutter with black smoke, sealed fireplace no access for burning wood, paper etc.
What might be the cause? and any concern for future?

I am not really a help as to why but I ran into the house with the same problem. It was in a corner under the sofit. The installation conformed to the manufactures specs but I still advised to have a specialist come in and evaluate due to the black heat/smoke marks that were present. The client never called the specialist so I don’t know why but the house has yet to burn down so that is good.

I did have a guess about it not getting proper draft because of it was in a corner but that was just a WAG.

Direct vented gas appliances are mechanically vented, they have sensors that will shut them down if there is no draft. I think what you are seeing is caused by condensation. The black could be mildew or other condensation based staining. It carries on beyond the vent location, what did the rest of the bottom roof perimeter look like?

This is an overall view of the rear, Staining was even on brick above vent, not sure if you can tell from this point of view, top of vent also had the black smoke stains.