Quick pressing and releasing of the test button may not make it trip,
try
holding it in for a few seconds, a count of ten, to see what happens.

Yep, tried this, that didn't work.


If
it
doesn't trip after that, then you do have a fault on either RCCB or in
the
configuration of the connections.

Well, it did trip when first installed, so I "presume" the
configuration is OK. I opened it up today to check the little wire
coming out of it was connected to earth and indeed it was. Im
presuming (doing that too much these days) that my earth is OK, as the
socket tester Im using says earth is OK.

Is there anything else I can try? Or some test to prove for sure it is
the actual RCCBO that is knackered?