On 08/01/2014 22:47, Pete C wrote:
Can anyone tell me the most common cause of failure of automatic vent
openers please.

If the vent window jams, the auto mechanism will destroy itself (the
immovable object meeting the irresistible force! But the latter will
prove to be resistible, I'm afraid). In the end either the seals will
go, or something will distort.

I've only had one auto vent opener fail in over 30 years, and that was
through a jammed window.

By the way, be /very/ careful if you do find the window has jammed. If
the auto opener is still working, and the window suddenly comes loose,
it will be flung open with extreme force. If the opener fixing comes
off the window, the window is likely to pivot all the way back onto the
roof glass, or come loose completely if you are very unlucky.

--

Jeff