I recently took out a Pellet burner in corner of internal room that heated water and had flue and plumbing pipes boarded over with plasterboard at angle to walls (135 degree in room, 45 degree behind plasterboard) from floor to ceiling. The flue was capped at bottom and pipes sealed by plumber before plastering. Now I have noticed wet edges on plasterboard where it joins ceiling. Also a small rectangle in middle of main board where a smaller board was used to fill in a rectangular hole where Pellet burner pipes had come through shows a wet rectangle (edge of small rectangular inserted plasterboard) Any ideas why please? Could it be condensation from the metal flue pipe? Should the flue have been sealed at its lower opening? Do I need some kind of vent (doesn't go to an outside wall) Any thoughts appreciated, thanks
Condensation could be the cause. Cut hole and peak in. Leave a few days to see if it dries. Fit vent then