I'm at a loss.
For two night in a row, one of the circuits that feed the power outlets to half my house randomly trips. It also feeds the gas hot water system, range hood, cooktop and outdoor IP-rated power outlets (those are under cover and have nothing connected). The breaker has an RCD built-in.
On Monday night, the breaker tripped and I was unable to reset it. I went around and disconnected everything I could from that circuit but it would trip off straight away. Tuesday morning, I could reset it just fine and it remained on most of the day (with everything re-connected and operating just fine). Electrician came around yesterday and did earth leakage tests while I went around and connected everything back. Nothing. Everything showed normal.
Last night came around and it trips again, same deal, unable to reset it. This time I crawl up into the roof, disconnect the range hood and also the hot water system and cooktop. Still unable to reset it. This is with absolutely nothing connected to it. On both occasions, I wasn't doing anything in particular. Just on the computer.
I thought maybe water or humidity is getting in somewhere, but it hasn't been raining and it's quite dry at the moment. Besides, in the mornings it's quite dewy and moist, but the breaker is able to be reset.
It's not a case of overloading either. Fully loaded, that circuit would probably be a few hundred watts at most (without the coffee machine or toaster operating).
What are the chances of a faulty RCD? The electrician said it's extremely rare for it to be the cause. I am honestly scratching my head as to what it could be. I should also point out that it's a relatively new house, well under 10 years old.