Nuisance RCD tripping questions

[RF Lighting]

I had a random trip on our RCD at home.

It would go maybe once a week and then maybe nothing for 2 weeks and then 3 times in a morning.

It was eventually tracked down to a slight leak on the cold pipe supplying the header tank in the loft.

This was soaking through the fibreglass and then was either dripping down the stud wall or wicking down the cables into a dry lined socket.

I only tracked it after water started dripping from the living room ceiling!

Could have got the megger out and tracked it, but where's the fun in that?

 

[DUB88]

Ok a little update. I was on nights last night but the wife said she'd noticed the electricity tripped off when she was up at 2am. She reset the RCB that had tripped and now she says she thinks the MCB beside was also gone but she was half asleep. This is for the downstairs sockets.
I have just put a socket tester on all the sockets and one is showing no earth. The earth line look to be connected fine so I just swapped the socket for a known good one but still the same, no earth.
Now there has been no load on this socket but this socket is the last of the old house before the extension begins. All the sockets test fine in the extension so could this be the problem? There was no load on this socket but I can't remember what position the switch in the socket was in before I started messing with it..