Why Are My Lights Flickering? 7 Common Causes and Fast Fixes

First — is it dangerous?

A single flickering bulb is rarely a hazard. But if you see multiple lights flickering across the house, or hear a crackling sound at the fuse board, that is a sign of a loose neutral or line connection — and it can start a fire. Turn the circuit off and call an electrician the same day.

If you are unsure, book an emergency callout or call 0203 503 1240 — we cover the whole of London.

Cause 1 — LED bulbs on an old dimmer

By far the number one reason we get called out. Traditional dimmers were designed for incandescent and halogen bulbs that drew 40 – 100 W. Modern LEDs draw 3 – 10 W and behave completely differently on the wave-form.

Fix: Replace the dimmer with a modern trailing-edge LED-compatible dimmer (Varilight V-Pro or Lutron RA2) — usually £60 – £90 supplied and fitted.

Cause 2 — Cheap, non-dimmable LED bulbs

Non-dimmable LEDs on any dimmer will flicker, buzz or stay dim. Even on a plain switch, ultra-budget bulbs from unknown brands often lack capacitive filtering and flicker in sync with mains ripple.

Fix: Buy known-brand LEDs (Philips, Osram, Integral, Aurora) rated for the fitting.

Cause 3 — Loose terminal in a light switch or ceiling rose

Vibration, thermal cycling and DIY errors gradually loosen connections. A slightly loose neutral behind a switch can flicker one or two lights on the same circuit.

Fix: Isolate the circuit, expose the terminal, re-terminate and torque to spec. Book fault finding for this — probing live is not safe.

Cause 4 — Voltage sag from a large appliance

Kettles, showers, induction hobs and heat pumps pull heavy inrush current. If the incoming supply or tails are undersized, you will see a momentary dim every time the appliance switches on.

Fix: Have your incoming supply and tails checked. Older 60/80 A supplies often need upgrading to 100 A via the DNO.

Cause 5 — Failing consumer unit or MCB

Old BS 3871 MCBs and worn Wylex Standard fuses develop high resistance over time. Under load they warm up, expand, and briefly interrupt the circuit.

Fix: A consumer unit upgrade will almost always resolve this — see our consumer unit upgrade guide.

Cause 6 — Bad joint in a junction box or ceiling rose

Very common in period properties. A wire has been twisted rather than clamped, or a chocolate-block terminal has burned. You will often smell burnt bakelite.

Fix: Trace and replace with proper maintenance-free terminals. If joints are hidden inside floors and ceilings, we use infra-red thermal imaging to locate hot spots.

Cause 7 — The neighbourhood supply

Occasionally the fault is not in your house at all. If every home on your street flickers at the same time, the problem is with UK Power Networks (UKPN).

Fix: Call UKPN on 105 (free from any phone). They will send a jointer, usually within a few hours.

When to call an electrician

Book an electrician the same day if you notice any of these:

• Multiple lights flicker at once
• A burning smell or discoloured switch plate
• The consumer unit is warm to the touch
• Sockets crackle, pop or spark

Do not keep resetting a tripping RCD — that is a symptom, not the cause. Get in touch and we will diagnose properly.