Mystery damp...

[BenHutton]

We have a mystery damp patch on one of our upstairs chimney (unused) breasts. Have had the chimney repaired/repointed by various people but the damp remains. It's not really getting any bigger over time so don't think is water ingress. Directly below it is a cooker installed in the closed up fireplace in the kitchen. There's a cooker hood that vents through the breast and out the wall. The integrity of this is maintained.

Anyone got any clues? Possible that the big warm cooker is slowly heating and condensing the air in the chimney? Is so how do I go about preventing this? Any help would be greatly appreciated.

 

[Diver Fred]

Is the chimney 'Capped' and 'Vented' If the Chimney isn't capped then rain will get it. You do need a gap at the edges of cap to keep the stack ventilated.

 

[BenHutton]

So I'm pretty sure it's capped. So no rain but a bit of air can get in.

 

[Doggit]

Go and have a look in the loft. those marks are oddly just below the ceiling line.

 

[bobasd]

photos of the outside wall,and chimney stack showin any terminal please.do you have photos of the work you mention?
you have two seperete flues , one for the kit and one ffor the bedroom.
were these flues swept before?
theres no through ventilation from the kit up and out to the stack terminal.this causes a sort of condensation in the flue that might show on your decorations.then again it could be condensation but that usualy has mould spots.