Well in my case its the little bolt that slides up into a metal bit on the
frame. What seems to happen is that the door twists slightly making it catch
the edge. I filed it a bit and it seemed ok for a while but is binding again
I notice.
I bet quite a few people find this problem in one form or another as there
are now so many sliding and pushing bits to keep the door shut, it seems to
not need much for one or more to start binding up.
Brian

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From the Sofa of Brian Gaff Reply address is active
"Tinkerer" wrote in message
...
We have a pair of UPVC doors on our porch. One is only opened when
required for large items to be taken into the house and it carries the
frame into which the "everyday" door locks.

We have found that the locking mechanism for the "everyday" door works
fine until the sunshine arrives. In the afternoon sun it presumably
gets very hot and the handle will only lift just over half the normal
distance which is not sufficient to allow the key to be turned although
I do not think the problem is the handle as it operates fine when the
door is open. Once the sun is off it the locks work fine again but
that is no use if you need to lock up during the afternoon.

I can't imagine that we are the only people to have experienced this
problem. I assume that the door is expanding/bending in the heat and
some adjustment is required. Problem is that I cannot identify which
part of the umpteen part locking system is jamming. I was wondering
if anyone else had experienced the same problem, or is familiar with
this type of door, and could suggest how to find where it lies.

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Tinkerer