It is often difficult to find the cause of a damp patch which seems to relate to a chimney as it could be a wall , gutter or roof defect that is the cause. A good place to start is by having the flues inside the stack swept through as this shows whether the lining is dry, damp or wet.
If the chimney stack has an open chimney pot then an approved rain hat or cap can easily be fitted to keep the rain out.
An inspection of the top of the chimney stack will identify any cracks or gaps in the mortar covering the top holding the pots in place and a quick survey of the roof around the stack could see any defects letting in rain.
SMOKE COMING BACK INTO THE ROOM
Smoke not going up the chimney and coming into the room can be caused by two different problems or both together.
A simple Smoke Evacuation Test will show whether there is the sufficient ventilation . A from the ground survey will see whether the chimney is tall enough.
SMELL OF SMOKE IN ANOTHER ROOM
If there is the smell of smoke in another room then Building Regulation Test No 1 must be carried out. By filling the chimney with non toxic smoke then sealing it top and bottom creates a small pressure inside .The chimney is then thoroughly inspected inside and out for leaks.
There are other reasons for this problem which are very easy to cure but the cause does need IDENTIFYING and RECTIFYING due to the risk of Carbon Monoxide Poisoning!