Why will my circuit breaker not reset?

The ordered half-split method that finds why a breaker keeps dropping, and the point at which the answer is that the fault is in the wiring and not in anything you can unplug.

Difficulty: beginner
Time: 25 min
Read: 5 min
Safety: warning

Short answer

Turn everything on that circuit off and unplug it, then reset. If it holds, the fault is in something you unplugged — bring items back one at a time until it drops. If it will not hold with nothing connected, the fault is in the fixed wiring or an accessory, and that circuit stays off until an electrician tests it.

A breaker that refuses to reset is not sticky or worn out — the overwhelming majority are doing exactly what they were designed to do, which is refuse to close onto a fault. The job is to shrink the search area by halving it repeatedly, and there is a defined point at which the answer stops being yours.

Safety

A breaker that will not reset is holding back a live fault. Do not force it, hold it up, tape it or try repeatedly — each attempt re-energises the fault. If it will not reset with every appliance on that circuit disconnected, the fault is in the fixed wiring and the circuit must be left off until an electrician has tested it.

What you'll need

a torch
a phone to photograph the board
a written list of what is on the circuit (optional)

Half-splitting a circuit that keeps tripping

Step by step

Identify exactly which device is down and write it down.MCB, RCBO or RCD, and which circuit it is labelled as. If it is an RCD covering several circuits, the search area is everything behind it, not one room.
Switch that circuit's own MCB off before doing anything else.Working with the circuit deliberately isolated rather than half-reset means nothing re-energises while you are unplugging things.
Disconnect every load on that circuit.Every plug out, not just switched off at the socket. For a lighting circuit, that means every light switch off, and it is worth removing bulbs from any fitting you suspect. Note that a switched-off appliance is still connected.
Reset once, deliberately.Push the switch fully down first, then firmly up. Half-throw is a genuine reason a breaker appears not to reset. If it holds now, the fault is in something you disconnected — go to the next step. If it drops again immediately with nothing connected, stop and go to the last step.
Half-split the loads, do not go one at a time.If there are twelve things, plug in six and see. If it holds, the fault is in the other six; if it drops, it is in those six. Halve again. Twelve items takes four tests this way rather than twelve.
When you reach one appliance, confirm it twice.Plug the suspect into a socket on a different circuit and see whether it trips that one too. If it does, the appliance is faulty. If it does not, the problem may be that socket rather than the appliance.
Look for the pattern rather than the item if nothing single is guilty.If it only drops when three or four particular things are on together, that is an overload, not a fault, and the answer is to spread the load or add a circuit. If it only drops in wet weather or when the shower runs, that is earth leakage with a physical trigger.
Check the obvious physical causes on a lighting circuit.A bulb that failed in a flash, a cheap LED whose driver has failed short, or water from a bathroom above tracking into a ceiling fitting. Replacing a blown bulb with the circuit isolated is owner-level; opening the fitting is not.
Stop at the fixed wiring.If the breaker will not hold with every load disconnected, the fault is in the cable, a socket, a switch, a junction or a ceiling fitting. Leave the circuit off, label it "do not switch on", and call an electrician. That circuit is not usable and there is no owner-level next step.

Tips

Record the time of day and the weather each time it happens. Two data points often identify a timed immersion heater or a rain-driven outdoor fault in minutes.
Freezers and fridges are the loads people forget to check for after a trip. Look at them first when power comes back.
Never wedge or tape a breaker up. It is the single most dangerous thing a householder does with a consumer unit, and it removes protection from a cable that is already telling you something is wrong.

Common mistakes

Resetting repeatedly to "see if it holds this time" — Each reset drives the fault current through the fault again. On a short circuit that means repeated arcing at the damaged point, which is how a fault that was going to be a repair becomes a fire.
Only switching appliances off rather than unplugging them — Most appliance switches break the live only, and many break nothing at all in standby. A switched-off appliance with a leaking filter or a damp motor still trips the RCD.
Assuming a breaker that will not reset is worn out — It happens, but it is rare and it is not a diagnosis you can make from the front. Assuming it means the real fault stays live behind a device that is then trusted less.

If it doesn't work

Breaker feels like it moves but does not stay up

Cause: Not thrown fully off before resetting, or a genuine fault holding it — Fix: Push firmly all the way down, then all the way up in one movement. If it still will not stay, treat it as a fault.

Holds with nothing plugged in, drops the moment one appliance goes in

Cause: That appliance is faulty — Fix: Stop using it. A trip on a different circuit as well confirms it. Repair by a competent person or replace — do not keep it in service.

Holds all day and drops overnight

Cause: A timed load such as an immersion heater, storage heater or freezer defrost cycle — Fix: Work out what runs at that hour and test it deliberately during the day.

Will not reset with everything disconnected

Cause: Fault in the fixed wiring or an accessory — Fix: Leave it off, label it, and get an electrician to test insulation resistance on that circuit. There is no owner-level fix.

Whole board goes off, not one circuit

Cause: Main switch, or an RCD covering everything — Fix: Switch every circuit MCB off, reset the main device, then restore circuits one at a time to find which one causes it.

Questions people ask

Can I just leave that circuit off and carry on?

For a short period, yes, and it is far better than repeated resetting. But a circuit that has faulted is telling you something about the installation, and an unexplained dead circuit is exactly the kind of thing that gets quietly bypassed with extension leads, which is its own hazard.

Why did it trip once and then behave for a week?

Intermittent faults are usually moisture or a connection that is loose enough to arc under load and then settles. They almost always come back, and they usually come back worse. Note the date; if it happens twice, get it tested.

Is it safe to use an extension lead from another room until it is fixed?

As a short-term bridge for a low-load item such as a lamp or a router, with the lead run so nobody trips on it and never under a carpet, yes. Not for a heater, a kettle, a washing machine or anything else that draws real current, and not as a permanent arrangement.