damp external wall

Hi So, about 18 months ago I noticed some damp coming from behind a radiator in our downstairs toilet. The house is 3 years old. The damp didn't get any worse for 12 months, but it didn't dry up either, so to be honest, I just ignored it. We've had a bit of rain recently, not much though...

We've had a problem with damp in our kitchen cupboards since we moved in. Only against one of the external walls. This is a single story outshoot from a sandstone building (I would say extension, but all the houses have them so I suspect they were built with them) The outshoot is brick and...