Lights flickering? Causes and when to call an electrician

Count the lights before anything else

How many lights flicker tells you more than how they flicker. A single fitting is a local problem, a whole room points at the circuit, and the whole house points at the main connections or the supply coming in.

One fitting: lamp, holder and dimmer

Turn the light off, let the bulb cool, and check it is screwed or pushed fully home. A lamp that has backed out of its holder makes intermittent contact and flickers as it warms up. If it still flickers, move it to another fitting. A fault that follows the bulb is the bulb.

LEDs on dimmers cause more flicker complaints than anything else. A bulb that is not marked dimmable will flicker or fail on a dimmer, and an older dimmer designed for filament bulbs often needs a larger load than a few LEDs provide. NICEIC lists both as common causes. The fix is a dimmable lamp and a dimmer rated for LED loads, and the dimmer's minimum load matters as much as its maximum. Downlights with separate drivers add one more component that can fail, and the replacement has to match the fitting.

Flicker when the kettle, shower or washing machine starts

A slight dip in brightness as a large appliance starts can be normal on a long circuit. A pronounced dim, or a flicker that comes back every time the shower or the oven switches on, is different. It usually means resistance at a connection somewhere between the meter and the light, and a resistive connection gets hot under load.

That is the case NICEIC singles out as dangerous, because loose or damaged wiring can arc, and arcing is a recognised cause of electrical fires. An electrician will measure the voltage with and without the load and work back through the consumer unit, the meter tails and the main connections until the drop is found.

Whole house, and the neighbours too

If lights flicker throughout the house, check whether the neighbours have it as well. A fault on the street network is the network operator's to fix, and 105 is the free number for England, Scotland and Wales, whoever your supplier is. In Northern Ireland the number is 03457 643643.

The network operator owns everything up to and including the sealed main fuse, usually in the box under or beside the meter. Nobody but them should open it. Everything after the meter, including the cables into the consumer unit, is yours.

Note the dates and times when the flicker happens before you report it. A supply fault that comes and goes is far easier to investigate when the operator can match it to a time.

Signs that make it urgent

Flicker on its own is often harmless. Flicker together with any of these is not, and the circuit should be switched off at the consumer unit and left off until it has been looked at:

• a smell of burning or hot plastic near a switch, socket or the consumer unit
• buzzing or crackling from a wall, switch or fitting
• a light switch or socket that is warm to the touch, or discoloured
• breakers or RCDs tripping at the same time as the flicker

Those are on the warning list NICEIC gives householders, and each one points at a connection that is overheating.

What an electrician checks, and what it costs

Expect the visit to start at the fitting and work backwards: the lamp holder, the ceiling rose, the switch, any junction boxes in the loft, then the terminals in the consumer unit, which loosen over years of heating and cooling. On a dimmer complaint it is often over in minutes once the compatibility problem is spotted.

Diagnosis is typically charged at £60 to £110 for the first hour, which covers most flicker faults. A new fitting at an existing point is £60 to £120, and a fault found and repaired on the same visit usually falls between £90 and £250. For a dimmer problem, keep the bulb boxes or model numbers to hand, so the replacement dimmer can be matched to them.