In article , Ben
Edgington writes
"Richard Clay" writes:
When the gap appears, it looks like one of the long pieces has "drifted
away" horizontally from from the junction piece. With quite a bit of effort
and grunting, I pull it back horizontally towards the junction, where it
seems quite happy to sit (and I even clip it in). But after a while the long
piece drifts away again! How can this happen? I have to exert and grunt
quite a lot to get the piece back in, so what force can take it out again?
Immediately after I've put it back, there seems to be no "spring" action
that wants to take it out again - it seems to come out slowly over time.

A total guess, but it seems likely that it is caused by the daily
cycle of contraction and expansion due to warming from the sun. I
would have thought the expansion and contraction of a long piece of
guttering would be quite substantial and could well cause it to creep
over time and work its way out of this clip and through the other
clips.

This is exactly what causes it, our polycarbonate conservatory roof does
the same thing. Think this is why you don't get solvent weld gutters,
they always have rubber seals to allow some creep. Presumably the gutter
is gripped tighter by the clips at the far end than it is at the
junction.
--
Tim Mitchell