CH panel with 40 year old GFCI feeding 2 outdoor outlets and 8 indoor outlets. Nothing is plugged into any outlet. For 4 days I could not reset after trip (it immediately tripped again). Now it seems to work perfectly.
What is the likely cause and how best to troubleshoot?
How has the weather been lately?
Without knowing any more about your wiring, the likely cause would be moisture causing a ground fault at one of those outdoor receptacles. Was it wetter than usual on those 4 days, or perhaps a sprinkler got adjusted/moved?
I'd inspect those outdoor receptacles and their covers for moisture intrusion.
I have no idea what a GFCI actually is, or what makes it trip. Therefore, replace it.
Just kidding, of course!
Circuits are meant to flow current out the "hot" wire and back the "neutral" wire. Current is not supposed to go anywhere else. If it does, something is wrong, and if any of that current flows through a human, it could stun or kill them. If they fall or end up face down in water, a stun is a kill. This condition is called a "Ground Fault" hence GFCI is "Ground Fault Circuit Interruptor".
So, GFCIs compare the hot wire current going out to the neutral wire current coming back. If they are not equal, leakage is occurring and they trip.
So the best response to a GFCI trip is look for a ground fault. Start by unplugging anything fed from that circuit. If unplugging appliances works, then plug them back in 1 at a time until you find the tripper.
Or, the leak can also occur in the wiring, e.g. if mud wasps build a condominium inside an outdoor receptacle box. When that gets damp, it starts conducting electricity from hot to ground.
So you hunt for things like that, starting in the most obvious places.
If nothing is found, break the circuit at the halfway point by removing the downline hot and neutral. See if it still trips, and that will tell you which side of the break the problem is on. You can thus narrow down.
If disconnecting the Load wires from the breaker causes it to stop tripping and behave normally, that strongly indicates a problem with the circuit and not the breaker.
It's pointless saying the GFCI is defective until you've done those checks.
Most likely there was water, ( moisture) or insect infiltration in one of the outside outlets and the GFI was doing its job. It's almost impossible to trouble shoot a circuit that is working properly. It would be a good idea anyway to turn off the circuit and take a look at the outdoor outlets and see what they look like.
As indicated moisture is the most likely culprit but be aware that GFCI units do wear out over time and 40 years is a long time. If it happens again and doesn't reset with no apparent cause (moisture or a legit trip), you might want to replace it.
