I have a 2 storey 1970's house with an outside chimney. The problem is that I get some water dripping down the chimney in the winter. This is NOT associated with rain because it only happens from November to March when it is colder & has no correlation to whether it is raining or not. It only happens when the outside temperature is <about 7C And the heating is on in the room. For example it does not drip between bedtime & morning - I guess because the heating is off then. I'm guessing it is condensation when warm air from the room goes up the chimney & condenses in the top part of the chimney stack when it is cold. The chimney is not in use. I tried placing a board over the fireplace hole to restrict (not seal) the hole but this didn't work - it may even have been a bit worse. This problem started about 3 winters ago. Up until then no problems and there have been no modifications to house insulation for a number of years before that.
Another issue that I don't know if its related or not is that on the very rare occasion that we have had a fire we get small damp patches appear at the top left and top right hand corners of the fireplace where it joins the wall and along the top of the mantelpiece.
Any suggestions as to what I should do to solve this problem.