Why do my lights keep flickering, and is it dangerous?

If your lights keep flickering, the cause is usually something small: a bulb that isn't seated properly, an LED that doesn't suit its dimmer switch, or a fitting that is wearing out. But flickering can also be the first sign of a loose connection in the wiring, and that is worth taking seriously, because a loose connection gets hot.

This post explains the common causes, what the pattern of the flicker tells you, and the checks you can make yourself. Changing a bulb is fine, but never take a light fitting, a switch or your fuse box apart to look inside.

Is a flickering light dangerous?

Usually not. A single flickering light normally has a problem with the bulb or the fitting. But fire services list flickering lights alongside scorch marks and hot sockets as a warning sign of loose or dangerous wiring.

The reason is heat. Where a connection has worked loose, electricity jumps across a tiny gap instead of flowing through a tight joint. That creates heat, and over months it can damage the cable and the fitting around it, out of sight in a ceiling or behind a switch.

So the useful question is how far the flicker spreads. One light is usually just that light. Several lights, or lights in different rooms, point to the wiring or the supply.

The common causes, from simple to serious

A loose bulb. Bulbs can work loose over time, especially in a ceiling below a busy room where footsteps cause vibration.

An LED on the wrong dimmer. Many older dimmer switches were made for old-style filament bulbs, which use far more power. Fit a low-power LED and it can flicker, hum or never quite switch off. The bulb needs to say "dimmable" on the packaging, and even then not every dimmer suits every LED.

A failing LED. Every LED has a driver, a small circuit that turns mains power into what the LED needs. When a driver starts to fail, the light flickers. In many downlights the LED and driver are built into the fitting, so the whole fitting has to be replaced.

A worn switch or fitting. The contacts inside switches and lampholders wear over the years and stop making a clean connection.

A loose connection in the wiring. This can be at a switch, a ceiling rose (the round fitting a pendant light hangs from), a junction box in the loft or the consumer unit, the modern name for a fuse box.

A heavy appliance switching on. A brief, slight dip when a kettle, oven or electric shower starts is common. A clear flicker every time suggests a circuit or connection under strain.

A problem with the supply. If the whole house flickers, and your neighbours' lights do too, the fault may be on the network rather than in your home.

What the pattern tells you

Where and when the flicker happens narrows the cause down quickly:

• One light only: most likely the bulb, the lampholder or that fitting.

• Every light on one dimmer: most likely the dimmer and bulbs not suiting each other.

• Several lights in one room or on one floor: a switch, a connection or the wiring on that lighting circuit.

• Lights all over the house when big appliances come on: a heavily loaded circuit, or a connection at the board or where the supply enters the house.

• Your whole street: the local network.

Safe checks you can make at home

You can rule out the simple causes without touching any wiring:

1. Check the bulb. Switch off, let the bulb cool, then make sure it is pushed or screwed firmly in.

2. Try a different bulb. Use one you know works from another light. If the flicker stops, the old bulb was the problem.

3. Test the dimmer. If the light is on a dimmer, check the bulb packaging says dimmable, then run the light at full brightness. If it only flickers when dimmed, the bulb and dimmer probably don't suit each other.

4. Note when it happens. Write down which lights, what time, and what else was switched on. This pattern is the most useful thing you can give an electrician.

5. Ask next door. If your neighbours' lights are flickering too, call 105, the free national power cut number, which puts you through to your local network operator.

Don't unscrew a light fitting, take a switch off the wall or open the consumer unit. Even with the light switched off, there can be live parts inside.

When to call an electrician

If a new bulb hasn't fixed it, it's time for a qualified electrician. Some signs are more urgent:

• flickering in several rooms, or getting worse

• a buzzing or crackling sound from a switch, fitting or the consumer unit

• a switch plate or fitting that feels warm or looks discoloured

• a burning smell anywhere near a light or switch

• lights that dim sharply every time a large appliance starts

• flickering together with a switch tripping in the fuse box, which our post on why your electricity keeps tripping explains

If you can smell burning or see scorch marks, stop using that light, switch the circuit off at the consumer unit and treat it as urgent.

How we track down the cause

When we visit, we start by asking where and when the flicker happens, because the pattern often points straight to the cause. We then safely isolate the circuit and check the switches, fittings and connections on it, testing with specialist equipment rather than guessing.

Often the fix is small: a loose terminal made secure, a worn switch replaced, or a dimmer swapped for one that suits LED bulbs. Our lighting services cover LED upgrades and dimmers if you want the lights put right and improved at the same time. If testing shows the wiring itself is breaking down, we explain what we found and talk you through the options before any work starts. As NICEIC Approved Contractors, we test our work when it is finished and give you the right paperwork for it.

Some faults take patience to find. As one customer put it, we "found a breakage in the outside lights which other electricians could not find".

If your lights keep flickering and a new bulb hasn't solved it, JM Electric can find the cause and put it right. Book a visit through our domestic electrician service and we'll track down the fault and explain what needs doing.