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.

Solvent weld pipe should be used for condensate pipework, push fit isn’t really good enough. Internal pipework should be 21.5mm diameter and anything outside should be 40mm or larger to prevent freezing in bad weather.

Most jobs can be completed using the following items:

straight connectors

elbows

solvent glue

Junior hacksaw

Just remember to put the glue on the pipe and not inside the fitting. This way the excess glue scrapes off outside the pipe instead of filling the fitting.