The lights are on but the kettle's dead. Upstairs has power and downstairs doesn't. Half the sockets in one room work and the rest do nothing - and the fuse board looks fine. Nothing tripped, no drama.

That's the bit that throws people: power has gone missing and the board isn't even admitting it. We get this call constantly across London - terraced houses in East London where sockets have been added to for decades, conversions carrying three flats' worth of alterations in one wall. Partial power loss almost always has a boring explanation. But boring and harmless aren't the same thing.

What's likely behind it

Without testing, anyone naming a cause is guessing. What we can tell you is what it usually turns out to be:

A tripped MCB or a blown fuse on that one circuit. The single most common answer - and sometimes the breaker sits so close to ON that it looks healthy at a glance.
A failed connection at a socket, junction box or accessory somewhere mid-circuit. Terminals work loose over years of heating and cooling, and recent building work is a classic trigger.
A broken leg on a ring final circuit. Part of the ring goes dead - or worse, everything still runs while the surviving leg quietly carries the whole load.
Cable damage from drilling, rodents or corrosion. Least common, but it happens - usually announced by a picture hook that found more than plaster.

That broken-ring case deserves respect, because it's invisible from the kitchen. Sockets that still work aren't proof the circuit is healthy. On an inspection these faults come out as coded observations - the C1 C2 C3 codes electricians grade danger by - but between inspections there's nothing to see at all.

How quickly should you act?

Same-day. We're blunt about this one for a reason: partial power loss usually means a connection has failed or is failing, and failed connections are precisely where arcing and heat damage begin. The joint that killed your sockets may have been overheating for weeks before it finally let go - and if it's still arcing behind a faceplate, it isn't waiting politely for a convenient appointment.

Two consequences of leaving it. A failed joint that took the power out can keep cooking the cable around it before it fails completely. And on a split ring, the sockets still working can be overloaded every time the tumble dryer runs - with nothing visible until something smells.

A dead circuit that stays dead is an inconvenience. A half-dead circuit still carrying current is the one we take seriously.

Safe things to try first

Start at the consumer unit, before anything else. Look for a breaker sitting out of line with its neighbours or, on an older board, a dropped fuse. Push a suspect breaker fully OFF and then back ON - a half-tripped MCB can fool anyone.

If it re-trips straight away, stop. Leave it off. That's the installation telling you a live fault is sitting on the circuit, and repeatedly forcing it is how small damage becomes big damage.

Worth doing too: unplug everything in the dead area. A faulty appliance can take a circuit down, and if the breaker then holds with the room unplugged, you've learned something useful - remember which item was where.

And that's the limit of sensible DIY here. No faceplates off, no poking in junction boxes. The break is usually mid-circuit, hidden, and live on one side.

How we track it down

This is methodical fault-finding, not guesswork. We identify which circuit's affected and how it routes from the board - labels lie often enough that we verify rather than believe them. Then we test for supply at each dead point, which brackets the break: somewhere between the last live accessory and the first dead one is your fault.

Those two accessories get opened and inspected first, because failed terminations love hiding there. Once the culprit's found - a cooked terminal, a nicked cable, a lazy connection from an old refurb - we repair it and then re-test the whole circuit, ring continuity included, so a second weak point can't hide behind the first. Defects like these are what EICR testing London rental stock every five years keeps digging up; the only question is whether they get found deliberately or the hard way.

Getting the power back on

Most of these jobs resolve in one visit: the failed connection or damaged cable section is repaired, the circuit is proven end to end, and any related coded defects can be put right with certification to show for it. If the outage has taken down heating, medical kit or a security system - or anything found is too dangerous to leave energised - that's when an emergency electrician takes over instead of the next free slot.

Either way, the wrong move is the DIY bridge or the "it still mostly works" shrug. A repair done blind, with no continuity testing afterwards, can leave a circuit more dangerous than the fault did.

Dead circuits and the electrical safety certificate London report

If the property's let, there's a second reason to move quickly: a failed mid-circuit connection is exactly the kind of hidden defect an electrical safety certificate London inspection is designed to surface. Far better to have it found and fixed on your schedule than flagged on the EICR London letting agents ask to see before they'll market a property.

Call today if part of the installation has gone dead - and treat it as an emergency if a breaker won't hold, anything feels warm, or you can smell heat near the affected room. Every week a failing joint stays in service, the repair bill and the risk grow together.

Some sockets or lights are dead but others work in London