To confirm what you have said. You have removed a laminate floor from the area and the sub floor was dry. You have carried out work on a boiler and there is plumbing in the area. What works have been carried on or near water pipes?
A wood floor was installed and has lifted and your dry concrete is now wet. You should not have moisture (condenstaion amounts) on the sub floor. It is very unlikely it was this wet when the installer was laying it so the moisture has appeared after the flooring was installed. This is my guess.
Did the floor lift very quickly (over night)? This is a classic sign of a leak.
A floor lifts at the weakest point (usually the middle of the floor) and is commonly no where near the source of moisture and thus the source can be difficult to find.
A wood floor was installed and has lifted and your dry concrete is now wet. You should not have moisture (condenstaion amounts) on the sub floor. It is very unlikely it was this wet when the installer was laying it so the moisture has appeared after the flooring was installed. This is my guess.
Did the floor lift very quickly (over night)? This is a classic sign of a leak.
A floor lifts at the weakest point (usually the middle of the floor) and is commonly no where near the source of moisture and thus the source can be difficult to find.