UPVC Window/Handle problem

[ellal]

I've got two top hinged windows in a bay window that open and close ok, but the handles appeared stuck.
(not locked)

Took the handles off, and they worked fine.

Replaced into the windows and they wouldn't budge.

I have no clue as to the inner workings, so is there something I can do/check before getting a call out?

 

[Wayners]

Rusty mechanism?

 

[ellal]

Possibly.

Tried gently hammering the pins after loosening the screws on the bottom plate but with no luck.

Sprayed a lubricant (WD40) but not budging.

 

[RrogerD]

Does it all work fine with the windows open? If so, it's likely to be the window alignment ie catching on the catches when closed. This can occur as the hinges start to sag over time. Solution, put up with it and modify the way that you operate the window and locking or alternatively, replace the hinges.
If it is all still tight when operating with window open then as said above, likely to be the mechanism itself. Unscrew from window, measure overall length, positions of fixing holes and sizes of mechanism (it's all available online when ordering) and then replace with new ones.