Damp Plaster?

[RK_London]

I have some kind of damp patch appear on wall plaster on 2nd second floor bedroom. The plaster has flaked off. The bedroom was decorated 3 years ago.

The patch is near a radiator so I thought pipes might be leaking. Had the heating system checked and it's ok. The wall is below a window sill so I checked the outside wall and it looks sound - nothing to let in any water.

So I'm abit stumped as to what's causing the problem. I've attached a picture below (I've scraped away the flaky plaster). Any ideas as to what's going on?

 

[JohnD]

Stand back and take a wider pic of the whole wall please.

Include the radiator and its pipes

Is the floor concrete or wood?

Please also photo the ceiling of the room below.

 

[RK_London]

Floor is wooden with floor tiles.
Wider pic of wall and photo of ceiling directly below

 

[Wayners]

You can get a spy camera cheap like the sort to that fits to smartphone.
Drill hole and push it in.

Other option is find a builder or damp specialist with a camera.

I'll guess at window outside at corner of sill leaking.
Maybe

 

[RK_London]

Thanks. I'll take a more careful look outside at the sill - couldn't find anything first time round but given volume of rain recently maybe I've missed a small hole/crack.

If window sill check fails to find anything, will get my hands on a camera.

 

[Wayners]

I mask up frame.
Stick mastic nozzle on metal foam gun and jam in around frame.
Clean up and silicone.
Outlaws window looked perfect but was letting in water.
I put new silicone around but still leaked.
Foam stopped it.

Don't think it helps with sill not in wall.
Fitters cut the sill ears vs removing brick

 

[JohnD]

Photos of outside please

 

[Loofah]

Is that window seat insulated or have any ventilation?