Two floors show damp on the chimney breast

My chimney breast runs through the ground floor, a bedroom on the first floor and the attic. There is dampness on the chimney on the first floor and attic but not on the ground floor. I have closed the chimney flue from the bottom using chimney sheep for few months, has this caused condensation which is showing as the dampness? Or do I need to be worried about another reason for the dampness?

Mike - HA3

Asked: April 26 2018