bob wrote:
Ok, bit of history, used to have an opening to a conservatory which
was removed, space bricked up and window installed. 2 problems builder
didn't have correct soldier bricks at time of job so a 2 course gap
was left between sill and new wall. Soldier bricks inserted at a later
date so I am guessing the mortar that I can see between top of soldier
bricks and window would have stuck to the sill. Second problem,
glazing of window was done incorrectly (not cross braced) causes the
sashes to become out-of-square (jeld-wen inspection pointed this out).
Hence,I am replacing window and doing the job myself :-).

bob, the glass wouldnt move so my guess is that the frame twisted a bit
and that throws the sashes out a bit.
best thing is to take out the old window and put the new one up to it
and judge it from there.
there is no real problem. Just take your time and make sure you get it
fitting squarely and whatever way you seal it in wherher with silicone
(my favourite) or screws and then mortar on the inside that is easily
done.
If the brickwork is stepped out a little in front then a good seal of
silicone is best applied to the frame front edges If not you should
still seal it all round on the outside with clear or white silicone if
its a white window..
The most important thing you want to fix is getting it set in correctly
whether you wedge it or screw it is secondary. you have to be careful
you dont pull it out of line so be careful that the wedges are near the
corners rather than the centre.