Wet marks half way up wall

[Sillars]

Hello,
I am after some advice on some wet/greasy patches on a wall in my hallway. The house is about 100 years old and the patches have been there since we moved in about 4 years ago.

The wall is in my hallway (Not an outer wall) and appears to be solid. The heating pipes run up trunking on the adjoining wall but ive never seen any dripping coming from them. We tried having the wall re-plastered and I have used all manner of stain blockers but the marks keep coming back.

They seem to dry out and then reappear throughout a week but I haven't noticed any pattern with the weather or heating being on.

I've attached a couple of pictures. The marks also appear on both sides of the adjoining perpendicular wall at a similar height.

Any ideas what might be causing this and how to rectify it would be much appreciated.

Thanks
David

[wes56]

the trunking has a snap on capand will prise off a backplate or pipe clips. do that and have a look at the pipework for moisture signs..
was that wall originaly an outside wall?any signs of an old chimney breast nearby?
if you go the replastering route then use a sand and lime render mix, dont use any gypsum powder..
that render will block the staining from any remaining salts in the wall for a good few years.