Seized window lock

[freecycle]

I have 25 year old Anglian double glazing. On one bedroom window, I can insert and withdraw the key, but the key won't turn in the lock to lock the window. As my 2 year old grandson is staying with us overnight this weekend, and he's into everything that can be turned / switched / opened, I've very keen to lock the window. I've been squirting wd40 into the lock all day, but it's just the same. Can anyone suggest what else do do? TIA, FC

[Stuart Noble]

Put WD40 on all the moving parts, bolts etc. Try locking it with the window open. See what bit is sticking and give it a helping hand and/or a smear of vaseline. IME these locks suddenly work for no apparent reason

[freecycle]

Thanks for the reply. The key won't turn in the lock whetever position the handle is in. Are there any other releasing fluids that anyone recommends, or will pouring hot water on it help? FC