Crumbly plaster by radiator valve. Pipe leaking in wall?

[harrypotter]

The plaster by this rad valve is bulging out and crumbly. My guess is it must be a leak in the pipe to the rad. Any other ideas?

It is dry to the touch however and dry powdery plaster seems to fall out

 

[Wayners]

Might have been filled around and that filler is trapping moisturiser or a reaction with the lime plaster.

 

[ChrisJP]

Just hack off all the crumbly plaster/filler and investigate. If there's no apparent leak that you can see after a few days with the CH operating, fill back up with a suitable wall filler to make good.

 

[harrypotter]

What filler/plaster would be suitable for contact with copper?

 

[ChrisJP]

I would use good old Polyfilla built up in layers, but others may make suggestions that are better.