Gap between uPVC window frame and window sill

[tonysab]

We had an upstairs conversion done about 5 years ago, new gable ends were built and new windows put in.
I noticed recently that a slight gap has appeared at one end of the window frame, between it and the inner window sill. Only about 1 - 1.5mm at most I suspect (at the moment!). I wonder what could have caused this, it is at its widest at the end of the sill and the gap narrows about a foot in, the rest of it is then fine. I do not think the sill has moved and in fact if I open the window and try and pull the frame inwards (without using too much force), it does move slightly. So seemingly the frame has moved but its odd that only a little bit at one end. And not even all the way up the frame, only at the bottom.
The frames were fitted on top of breeze block type bricks, is it possible one of the fittings has worked a little loose - the side of the window is also the same side we previously had a bit of a problem with it sticking when trying to shut, so has been slammed a few times (although you'd think that would bring the frame and sill more together).
The sill is wooden. I can't see any screws/bolts when I open the window I suspect I may need to remove some beading or such like to access if required.
Any advice greatfully received.

 

[pinenot]

It sounds like normal shrinkage. You say the sill is timber, does this have an apron underneath it?...pinenot

 

[tonysab]

thanks pinenot - no it does not have an apron (thats the bit below the sill right?). I will try and upload a pic later. Thanks again.

 

[pinenot]

Yep, that's the bit under the sill, sounds like your sill is bowing slightly as it contracts more on the open top surface than the enclose/buried under surface, perfectly normal as the wood moves. An apron tends to hide this from view, but the gap will normally still be there and can be a draft route...pinenot

 

[tonysab]

Ah, one thing I didn't make clear here is that the frame does not sit on top of the sill, the frame sits on the brickwork I believe (with spacers or whatever underneath), and the sill is pushed up to the frame. So the gap is visible when looking down onto the sill as opposed to looking directly at the frame, if that makes sense!

 

[pinenot]

Oh! I think I know what you mean, but a pic will certainly help see that better...pinenot