A GFCI that keeps tripping is almost always reporting something real. It is the one protective device in a house whose entire job is detecting a condition that can kill a person rather than one that can damage the wiring, so the instinct to make it stop is worth resisting until you know what it is seeing.
What a GFCI is actually measuring
In a healthy circuit, all the current that flows out through the hot conductor returns through the neutral. A GFCI compares the two continuously. If they differ by a very small amount — typically around 5 milliamps — it opens the circuit in a fraction of a second.
A difference means some current is not coming back the way it left. It has found another route to ground: through water, through damaged insulation, through the metal case of an appliance, or through a person. That last possibility is the reason the threshold is so low and the response so fast. Currents well below the level that would trip an ordinary breaker are enough to be fatal, and a GFCI exists precisely to catch what a breaker cannot see.
Why it is not an overload, and why that matters
This is the most common misunderstanding on the subject. A GFCI does not care how much current the circuit is drawing. Running a heater and a hair dryer together will trip a breaker on overload; it will not trip a GFCI unless current is also leaking.
Getting this right redirects the whole investigation. If it were an overload, unplugging things to reduce load would help. Because it is leakage, the useful question is not “how much is plugged in” but “which one of these is leaking, or where is the water”. It also explains why a GFCI can trip with nothing plugged in at all, which otherwise looks inexplicable.
Water, and why it trips when it rains
By far the most common cause, and the reason ground-fault protection is required in exactly the places water occurs: kitchens, bathrooms, laundries, garages, crawl spaces and everywhere outdoors.
Outdoors is where most repeat tripping lives. Water gets into a box behind a fixture, into an outlet whose cover only seals when nothing is plugged in, into a light fitting mounted so it collects rather than sheds water, or into a splice that was made with tape instead of in a listed weatherproof enclosure. Once there is a damp path between a conductor and ground, there is leakage, and the GFCI does what it was installed to do.
The strongest clue available to a homeowner is correlation with weather. If it trips during or after rain and holds during dry spells, you are looking for water ingress, and the fault is the ingress rather than the device. Outdoor circuits and fittings covers why exterior work fails at connections rather than at fixtures.
A single appliance leaking to ground
Motors and heating elements develop leakage as they age. Moisture inside a motor, insulation degraded by heat, or a heating element beginning to fail all provide a small path to ground — sometimes only when the appliance is running, or only once it warms up.
Freezers and refrigerators in garages, old power tools, pressure washers, well pumps, sump pumps, space heaters and pond pumps are the recurring culprits. Older appliances with metal cases are the most likely, and an appliance that trips a GFCI is worth treating as a fault in the appliance rather than an incompatibility. It is leaking current to somewhere, and the case it is leaking into may be one you touch.
Wiring faults, including one that surprises people
Damaged cable — a staple driven too tight, a nail or screw through a wall finding a conductor, rodent damage in an attic, insulation degraded by heat — creates a leakage path that is completely independent of what is plugged in. This is the case that trips with nothing connected.
There is also a wiring arrangement worth knowing about. Where a circuit was originally wired with the neutral shared between two circuits, or where neutrals from different circuits have been connected together in a box, a GFCI on one of them will trip as soon as it is loaded, because some of its return current goes back on the other circuit's neutral. The GFCI sees a mismatch and is technically correct. It is not a fault in the device or in the appliance — it is the wiring arrangement, and it usually comes to light exactly when a GFCI is retrofitted to an older circuit.
A GFCI that has simply worn out
They do fail, and they have a finite life. The electronics degrade, and outdoor and garage units live in the harshest conditions. A GFCI from the 1990s in an exterior box has had a hard life, and nuisance tripping with no other explanation is a real possibility.
But this should be the last conclusion rather than the first, because it is also the most convenient one — replacing the device is quick, and if the device was not the problem the leakage is still there and now nobody is looking for it. The honest order is: rule out water, rule out appliances, then consider the device. Worth knowing that modern GFCIs are designed to refuse to reset when they have failed internally, so a unit that will not reset at all may be telling you it is finished.
What you can safely narrow down yourself
Unplug everything on the circuit, then reset. If it holds, plug items back in one at a time, leaving each for a while. Appliances that only leak when warm take time to reveal themselves. If it holds with everything unplugged, you have an appliance.
Note the weather. Keep track of whether trips coincide with rain, sprinklers, or humidity. That correlation is worth more than any single test.
Find out what else is downstream. One GFCI often protects several outlets across more than one room, and the fault may be at an outlet you were not thinking about. When it trips, walk the house and note everything that has gone dead.
Look at outdoor covers and fittings. Without dismantling anything: does the cover close and seal properly, is a fitting sitting where water pools, is there visible corrosion or staining.
That is roughly the limit of what is safe. Locating leakage on a circuit needs test equipment and access to conductors, and there is no useful homeowner version of it.
The one thing never to do
Do not replace a GFCI with a standard outlet to stop the tripping. It is the single most common response and it is the wrong one in every case.
The leakage does not go away — the only thing that goes away is the device that was detecting it. And ground-fault protection is required in wet locations precisely because those are the places where a person completes the circuit. Removing it in a bathroom, a garage or an outdoor circuit removes the protection at the exact spot it was installed to provide. If the tripping is genuinely a nuisance, the answer is finding the leak, not removing the instrument that found it.
The same applies to leaving a GFCI switched off and using another outlet instead. That is often reasonable as a temporary measure, but the leakage is still on the circuit.
What an electrician does
Measure the leakage rather than guess at it. That means isolating sections of the circuit to establish where the current is going, testing insulation resistance where cable damage is suspected, and inspecting the outdoor boxes, fittings and splices that are the usual source. Where a shared or crossed neutral is involved, that is found by tracing the circuit rather than by testing devices.
The repair depends entirely on the cause: sealing or relocating an outdoor fitting, replacing a damaged section of cable, correcting a neutral arrangement, replacing a failed device, or identifying an appliance that needs repair or retiring. What they have in common is that the GFCI stops tripping because the leakage is gone, which is the only version of this problem being solved.
If it trips constantly, trips with nothing plugged in, or comes with any heat or smell, it is worth having the circuit looked at rather than lived with. Bring your notes on weather and on what goes dead — both genuinely shorten the job.