Damp patches above chimney breasts

Hello, we bought an old house (1840) in May 2017. The previous owner refurbished the house just before we bought it. He replaced three open fires on the ground floor, 1 with a log burning stove, 2 with gas fires. About a year after we moved in, damp patches have started appearing internally on the chimney breasts. They are a lot more visible on the first floor than the ground floor. The refurbishment included the roof and chimney pots. I'm wondering if the new sealed units at the ground floor have stopped the air circulating within the chimneys which is now causing these damp patches. What are my options for resolving these issues?