Brief description of problem.

Electric sockets only are tripping randomly - happened four times
since moving into our new property on 22/5/09. The first time was two
days after moving in, when barely anything was plugged in. The house
was rewired a couple of years ago and the previous occupants state
they had a similar problem, but it only happened to them a couple of
times in the 2 1/2 years they were there. The most recent trip was at
1am this morning. When it trips, only the electrical sockets in the
house are knocked out.

In locating the fault, I'm making some assumptions: chiefly that if
all of the sockets are turned off (ie. no device is consuming power),
its unlikely that anything could trip the RCB. With that in mind, the
only devices consuming power at 1am in the morning are fridge, freezer
and combi boiler all of which work on timers/thermostats. Therefore,
one of these devices (or the RCB itself) must be at fault?

The kettle was originally suspect - on two of the four occasions, it
had not long boiled when the trip occurred. I tested this two nights
ago by boiling a full kettle load of water (twice) and then pouring it
away. Tripped both times a few minutes after boiling when the kettle
was off its base. Tried plugging the kettle into the living room
sockets instead - tripped. Replaced kettle. At 1am this morning
however when it tripped, the kettle hadn't been used for several
hours.

Is it possible the RCB is a fault? I can leave the fridge and freezer
doors open, combi boiler running and it doesn't trip so could it be a
fault with one of these causing a power spike when it's timer/
thermostat kicks in? Or is the RCB too sensitive?

Please help!