Paint bubbling and flaking off wall

[Yorky]

I noticed that a line about a cm thick has appeared on both sides of an internal wall. When touched this line is puffy and then flaky and powdery underneath. The wall hasn't cracked, just the paint is affected.

Does anyone know what may be causing this? The house is two years old.

I've taken some photos of the wall from both sides:

http://i238.photobucket.com/albums/ff250/Kilnadrain/P1020768.jpg
http://i238.photobucket.com/albums/ff250/Kilnadrain/P1020763.jpg
http://i238.photobucket.com/albums/ff250/Kilnadrain/P1020761.jpg


I've had a very close look at the valves and one of them has a minute leak which is dripping onto the floor but this is not porous. As I say, the leak is so minute I can't see how this would be working its way under the floor and then up the wall.

The radiator in question was recently (last August) moved from another room as the original one was not providing sufficient heat output. It was too long for the existing pipe connections so one side was extended using an elbow,length of pipe and another elbow. There is some play in the pipe and, if there is leak, it may be at slab level where the elbow connection from the pipe running along the floor is fitted to bring the pipe up to meet the radiator. I fear that this elbow connection may have been disturbed and that is where the leak is. Is there any way of telling without ripping up the floor, including the concrete finished floor?

[Yorky]

Thanks again for the replies. The plumber came back and fixed the drip on the valve which was so minute that there was only one drip on the floor after twenty four hours of wiping it. I just cannot see how the water was getting through the floor as the floor is laminated and it wasn't dripping onto a joint.

I suggested there may be a leak elsewhere, such as on the elbow joint within the finished floor, and asked for a pressure test and/or to tie up the ball-valve to see if the level drops over a few days but the system is pressurised so this is not possible. There is, however, a central heating pressure gauge in the airing cupboard and the plumber suggested aligning the red adjustable pin with the actual gauge pin to see if this changes over a couple of days - is this an accurate method of assessing whether there is a leak or not?

Assuming there is a leak, I asked the plumber what methods of leak detection are there and he said that the floor would have to be dug up. Surely some sort of non-invasive testing can be done first?

I've just checked it and it is now measuring 0.8 bar and the setting last Thursday was 1.2 bar - does this mean there is a leak?