Leak ? through concrete floor. Probable cause?

[Adaptor]

We have a stain on the carpet in an inner corridor on the ground floor. Recently the patch has been damp, with moisture coming from underneath, so it seems. The floor is concrete , with old parquet floor, and then carpet over. Over the last 2 years, the patch has been damp on 3 occasions. There is a washing machine in an adjacent room but no signs of damp in that room, and gas central heating.

The damp became apparent again during the dry spell earlier this autumn.

What would you suggest to investigate/remedy

 

[Ookysoft]

Not a qualified plumber, here, but......

....what you 'could' look at, is any radiator linked to any pipe running in/under the concrete there. You may find the rad/valve/connection leaking and running down the pipe and along under the concrete until it pools or finds thimmer concrete to rise though. Don't just look at the nearest - look along that run at any rad's - feel for water when hot and cold - all round the valves - if dry right now then feel for residue where it may have been leaking etc..... If that area is regularly warm under foot when the heating is on, probably a pipe there.