When i had to replace the furnace ever since I have had problems with a pipe coming from the furnace that is hot to the toucch when furnace on. This pip previously was just open at the base to the outside.
The heated pipe causes ice dams wound it and snow melts that leak right in ti the kitchen below. And then runs underneath and is causing staining and water damag.-that I hac never had in fifteen years. Have had ice cam leak at the wall but never all the way down.
I am not for sure but it sounds like the flashing around the pipe that meets the roof deck was improperly installed.I would have a pro look at the installation of the flashing around the furnace pipe.Could you post a picture from the ground?