Fault current indicator - what should I do?

Question

Part of the power plugs in my flat stopped working this morning. I checked the breakers box and one of the breakers was in OFF position, with a yellow indicator.

After checking the producer's website, I've come to the conclusion that this means fault current. Here is the exact model:

I've disconnected all appliances from the power plugs and tried to reset the breaker, but it returns to the OFF position with the same yellow indicator.

My electrical engineering skills basically resume to those needed to change a light bulb, but I would like to understand if there is something I could check or do in this situation before calling a qualified electrician.

I'm also interested in a (layman's terms) explanation why the breaker is indicating fault current when there are no appliances connected.

Answer 1

Yellow indicator here indicates there was a difference between live and neutral current and the difference is suspected going somewhere it shouldn't.

The fault may be not only in some appliance, but also somewhere between the panel and the receptacles, over the wires hidden in the walls.

Usual reasons include, but are not limited, to:

1. Moist or water leaking near the wires, receptacles or distribution boxes. The leak may be hidden in the wall for a while.
2. Insects, dust or mice at the same places (cockroaches?)
3. An insulation of some wire degraded because of overheating (lighting fixtures?)
4. Some hard-wired device (that cannot be unplugged) failing. (Water heater is the first suspect, cooker is the second, air condition third)
5. The protection device itself malfunctioning.

Good luck!

Answer 2

The yellow indicator means it tripped on a residual current fault.
This probably means you have a short to earth, in an appliance, lighting fixture or due to water leaking somewhere.

Note that this is an RCBO, it trips on both overcurrent (16A B-curve) and residual current 30mA type-A, where only residual current shows the yellow indictor.