I'm really talking about the ones at the top which open outwards about a
horizontal axis (I don't know what they are called, sorry).

It seems, to me, to be a common problem that they will not fully shut -
well, none of mine will. So :-

a) If it is as common as I think, why won't they shut? Too many layers of
paint? Wood has expanded? Other?
b) What should have been done, or not done, to prevent this problem?
c) What is the most cost- and/or effort- effective way of curing the fault?
d) What, if anything, can or should I do to stop it happening in the
future?

Thanks in advance.

--
GPG