You have solved a problem by just seeing part of the big picture and recommending a contractor to come and (repair as necessary).
I had a good example of this last week almost missed a life threating problem myself. Part of the problem was very obvious even to the blind. Owner recently had a WH installed with the flue pipe traveling down hill to a old masonary chimney in a basement it was back drafting completely it was blowing the flame on my Bic lighter out before I even got it close to the draft hood.
To complicate the carbon monoxide problem even more there was a upflow 80% gas fired forced air furnace installed along side the WH. The return air duct connected at the bottom of the furnace had a grill installed taking return air from the basement and distributing CO through out the home.
The return air grill and the improper flue pipe on the WH I saw in about 2 seconds what I did not see imediately was the flue pipe on the furnace had a 45 degree rise connecting to the same masonary chimney in the basement with a short run between the outlet of the furnace and the masonary chimney. I assumed the natural draft from the furnace was performing as intended so I did not do a draft test with my Bic lighter. Visually it appeared to be fine wrong wrong wrong.
It took a while before my brain bell started to ring as I had already been on the roof with my spider man shoes One chimney penetration was all that was visible WHOA is me I have two chimneys inside one in the living room and one in the basement 20 feet or more from each other.
Next stop to the attic I go. WHOA again the chimney from the basement has been terminated in the attic Ya know the one with the two flue pipes connected to it in the basement and the return air grill about 5 feet away HMMMMM
Bottom line don’t assume;-)