fixmyplumbing

This could be the condensate pipe from a modern condensing boiler leaking. Follow the pipe to see if it connects to the bottom of the boiler. Condensate pipework leaks tend to only happen when the boiler is operating as that is the only time the condensate is produced.

The pipes come in 2 types push fit and solvent weld.  Push fit can be taken apart cleaned up and refitted.  Solvent weld pipework is fused together with solvent glue so can never be taken apart again.

If solvent weld pipework leaks it generally has to be replaced.  You can cut out sections and replace with push fit or even smear silicone sealant over the leaking part in an effort to block up the holes.  On condensate pipework there is no pressure inside the pipe so it is far easier to reseal than mains or central heating pipework.