I found this gutter problem posted on "The democrat and chronicle" website.
I’m writing in that hopes you can help us with a problem with the gutters on our older Cape Cod-style house. Since the installation of a new roof (tear off) and gutters, we’ve had a problem with water spilling out of one area of the gutters during a hard rain.
This part of the gutter is regularly cleared so there isn’t blockage. We’re uncertain if the pitch of the gutter is the problem or if we need a wider gutter in this area. We’ve had difficulty finding a company that has experience using wider gutters.
We’d welcome any suggestions about whom we might contact to assist with this problem.
I have seen and have solved this problem more than once. When a roof is installed the old roof is first removed. It is common for a some of the debris to wind up in the gutter. Most likely what happened is a piece of shingle fell into the outlet/drain and got lodged in the elbow. When it rains the water still flows down the downspout but at a much slower rate. I am sure it is a piece of roofing because the poster said the problem only started after the new roof was installed.
It is also stated "the gutter is regularly cleared so there isn’t (a) blockage." The problem with this statement is you wont know there is a piece of shingle in the downspout unless it is closely inspected or taken apart. Also, many gutter cleaning companies will clean out the gutters and then neglect cleaning out the downspouts.
This home owner is reaching out for answers and is planning on installing a new gutter system all because of a little piece of roofing.