Damp Patch and Slight Darkish Stain on Bedroom Wall

[Mountlands]

I have a slight stain and some damp patches on a bedroom wall near the top of the wall. This has appeared in colder weather and is worse after rain. My roofer says there is no roof leak he can see, there is a capped flue with flashing for a gas fire inserted 3 years ago but this has no sign of water ingress. I’ve had gutters cleared as these were pretty blocked. There are 2 more unused flues and at least one has been filled with rubble , I can’t see the other one. There is one lower vent on one of the flues in the bedroom and I have just cleared a bucket of rubble from this and established an air flow by holding a candle to the opening. In rain today the wall is damper again . My questions are
1. Will if take some time before I see any improvement in damp now I’ve got an airflow in one flue where the damp was showing ?
2. Should I try and clear the rubble from the truncated chimney in the loft - could this cause any structural damage , should I get a builder to do this !
3. Would directing a heater fan at the vent help it dry the rubble if this is indeed the cause of the damp.
4. Should I strip wall of plaster and ‘smash’ it - a suggestion from a builder - what does this mean !

Any other advice appreciated

 

[Wayners]

Put plastic over.
Water under the plastic its a damp wall.
Water on the plastic will show it's condensation.

Sounds like a cold spot and condensation to me.
Go watch skillbuilder YouTube channel which covers this. See if that helps you.

The answer maybe start dealing with the excess moisture in the air. We currently have two dehumidifiers running ever evening. Condensation on the windows is telling you there is a problem.

You could have cold bridging in the wall as well at that spot.

 

[ree]

OP,
Why not post pics showing the interior & the exterior - perhaps post annotated pics of each item mentioned above?
Did your "roofer" provide pics?