UPVC windows won't lock in the "ajar" setting

[MagMrMax]

Does anyone have any ideas on this, please? Thanks.

Moved into a house. Standard modern windows, quite new.

All the windows have 2 lock positions: fully closed and "ajar" (finger-width gap allowing air in but still locked).

4 of the 10 will go into either position fine.
4 of the 10 will fully lock fine but need a little wiggle to lock in the "ajar" position.
2 of the 10 will fully lock but won't lock in the "ajar" position at all. The handle will not go down as if it's being blocked by something.

Shootbolts all run smoothly up the vertical edge. They don't look bent (they work in the closed lock position, so I doubt that's the issue), and there are no shootbolts on either the horizontal upper or lower edges of each window. There are no visible obstructions to jam the mechanism, so I am mystified.

What is the solution, please?

 

[MagMrMax]

Anyone with even a guess?

 

[diy_fun_uk]

It's a difficult one to comment on without seeing the issue for real. In the bottom of the frame you'll have 'espag keeps' i.e. the metal bits that the window locks into. On the bottom of the opener you'll have rollers/lugs that locate into the espag keeps when the locking mechanism's engaged i.e. handle turned. When you're fully closing and locking the windows, do they lock quite easily i.e. without any resistance? Are the mechanisms in good order e.g. not rusting? When trying to close the windows in the vented position, can you bend down to watch the rollers/lugs as they move towards the espag keeps? Are they aligned or are they perhaps hitting the outer edge of the keeps, therefore stopping the handle as you turn it. Check likewise for the shootbolts.

I'm stating the obvious but it's either the shootbolts and/or rollers not aligning properly with their keeps in the vented position, or there could be a mechanism issue. However I'd probably rule the latter out given the windows all lock when in the closed position. The fact you have to wiggle some of them slightly indicates misalignment.

Hope this helps at least a bit. If you think pics help show the problem more, post some

 

[MagMrMax]

Hello.

I got the installation company to come out again. They said that the 4 "keeps" on the affected windows were ever so slightly out of alignment. They adjusted them and all is well.