In article , TheScullster
writes

"Phil Hughes" said:
My guess would be is that it is water getting in the seals, draining out
of the drainage holes in the frame, then running off the ends of the sill
as they haven't been sealed up.

Sorry I didn't describe things clearly enough, the sealant was continued
from the frame edge along the ends of the window sills.

I don't see how water that drains from the frame can escape. As explained
in the original post (perhaps not too clearly) there is a lip on top of the
sill just behind the front of the main frame, presumably to stop driving
rain being forced up under the main frame. Surely this also stops water
from draining away from the deliberate drain slots cut on the inside of the
frame below the opening window?

Had a similar thing myself in a window. Fixing involved taking the frame
out and sealing up the gap between sill and frame at the end.

Unfortunately I didn't see these fitted. Does the sill go in first, then
the window on top?
To check that I understand you, there is a gap under the frame which extends
up to the window opening. The sealant down the frame and alongside the sill
effectively goes over the top of this gap leaving a path for water to run
along the top edge of the sill just under the frame to the brick opening.
Is this the gap that you had to seal?


First of all, I should point out this is the only window I have ever
(re)fitted, so I am no expert. Its also a while since I did it, so my
memory might not be brilliant. However, from what I've read, what I
found is generally applicable to all PVC frames. As we've found, its a
bit difficult to explain in writing

The sill is fastened to the bottom of the frame with screws through the
bottom of the sill into the frame. There are mitred holes right through
the bottom of the frame that allow water that seeps into the frame past
the seals to drain out. The water drains out into the gap between the
frame and the top side of the sill, and then out to the front between
the bottom of the frame and the top of the sill. Thus unless the gaps at
the ends of the frame (where they butt up to the wall) have been sealed
*before* the frame and sill were installed, then potentially the water
can run out of these gaps. The sealant you see on the outside will not
fill these gaps.

Hope that's clearer. Maybe someone else can jump in here and confirm
this is generally the case.


--
Phil Hughes