Electrical fault finding in London homes

If some sockets have stopped working but no switch has dropped, the circuit is usually broken rather than leaking. On a ring circuit, the loop of cable that feeds most UK sockets, a loose connection at one socket can cut off the sockets beyond it. Sometimes the socket that has failed is behind a sofa or a fridge, not the one that seems dead.

A burnt or loose terminal can also run hot before it fails, so if a dead socket has scorch marks or smelled warm before it stopped, treat it as urgent. See our advice on no power to sockets but the lights work.

A tingle from a metal tap, sink or radiator can mean the earthing or bonding is not doing its job. Bonding is the green and yellow cable that links metal pipes to the main earth, so that if a fault makes a pipe live, the protection trips. Plumbing repairs with plastic pipe sections can break this link without anyone noticing.

If someone has had a shock, do not touch them while they may still be in contact with the supply, switch off if you can do so safely, and call 999. NHS inform sets out the first aid steps. Then leave the area alone until it has been tested.

Electrical Safety First says cables coated in black rubber were phased out in the 1960s, and lead or fabric coated cables are even older. Many London homes were last fully rewired in that era. The Valuation Office Agency counts 35% of Havering's homes as built from 1945 to 1972, and 29% of all London homes as built before 1919.

Old rubber insulation goes brittle and crumbles, particularly where cables are moved or get warm. Faults then come and go as the cable shifts. Fault finding on this kind of wiring often ends with advice on whether a repair is sensible or whether the circuit needs replacing. Our guide to rubber wiring in London homes explains what to look for.

Fault finding is methodical. The electrician starts by asking when the problem started, what you were using and whether anything has changed, such as building work, a new appliance or a leak. Then the affected circuit is isolated and tested.

The main tests are simple to describe. A continuity test checks that the conductors in a cable are unbroken from end to end. An insulation resistance test checks whether current can leak between conductors or to earth, which shows damp, damage or failed insulation. A polarity test checks that live and neutral are the right way round at each point.

On a ring circuit the electrician can split the ring at a socket and test each half, which narrows the fault down quickly. On a lighting circuit, junction boxes in the ceiling void are often where loose joints hide. Once the fault sits between two points, it can be found and repaired, then the whole circuit is tested again before it goes back on. You should get a minor works certificate for the repair. If the fault turns out to be part of a wider problem with old wiring, you will be told what the options are, with a separate quote.