Tripping RCD

[griff22]

Although similar to the Tripping RCBO thread, which I have read and tried to follow (I am a mechanical engineer, not an electrician!) this problem concerns a RCD that trips at apparently random times, usually when there is little being demanded eg in the middle of the night or in afternoon long after the kitchen has been in full use (hob, oven etc). Never when an appliance is being switched as far as I can tell.
What started as a trip which occured at intervals of a week or more has progressed to days and now, today, to 4 trips in 12 hours when only new fridge, new ch boiler and freezer have power on. This was since the electrician had done extensive checks and changed the main trip switch on the RCD. I understand that a couple of the circuits tested were slightly below 100% (below 299 - ?) but not enough to be the cause.
Can anyone help and advise, as far as possible in non-tech terms, please?

 

[EFLImpudence]

Any outside items that could be wet?

When you say that only fridge, boiler and freezer have power. do you mean that you have switched off everything else?
If so this will not help. You would have to disconnect the Neutral and Earth from the CU to completely isolate a circuit.
Obviously unplugging an appliance will eliminate a fault in the appliance itself.

Only proper testing can find these intermittent faults.

 

[PrenticeBoyofDerry]

If the electrician has been in and given your installation the all clear, we can only assume it's an item of equipment causing the problem.
When did the tripping start, when was the new boiler fitted and when did the new fridge arrive?
Did the tripping coincide with the new arrivals?
Is the boiler on a timer?

 

[Space cat]

Since this is a problem that's crept up slowly, I'd be looking for some part of the wiring where water or dirt could get in. Are there any outside lights or sockets?

Edit: Oops! EFLImpudence got there first.

 

[griff22]

My thanks to all 3 guys above.
Electrician continues to work his way round the house. The IR readings in one or two cases are down but (he thinks) not enough to cause trip (?).
They do seem to indicate damp / tracking as the readings fluctuate. Have particularly checked outside socket and disconnected feed to pond pump. Attached may amuse you - found during these checks and thought it was the answer causing tracking, but today (very hot day) another trip when hardly anything was 'on'. So more searching next week. I have also got supplier (Western Power) to agree to fit a voltage recorder to monitor supply. My thanks again - any further thoughts welcome!
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