Light switch buzzing or warm

A light switch should make a click and then nothing. If yours hums, buzzes, crackles or feels warm, it is telling you something. Sometimes that is just a dimmer that does not like LED bulbs. Sometimes it is a loose terminal starting to overheat. This guide helps you tell them apart.

If you would like an electrician to find the cause, our lighting and circuit faults page explains how a visit runs.

Two kinds of switch, two kinds of buzz

Switch type	Sound	Usually means
Dimmer, with LEDs	Faint steady hum, louder at low settings	Dimmer and bulbs not well matched
Dimmer, any bulbs	Hum plus warmth you can feel through the plate	Dimmer overloaded, or a poor connection
Plain on and off switch	Any buzz at all	Loose terminal or damaged switch
Any switch	Crackle, spark, flicker as you press it	Arcing at a connection. Stop using it.
Any switch	Burning smell, brown marks on the plate	Overheating. Switch off the circuit now.

A dimmer gets a little warm in normal use because it is controlling power. A plain switch should not.

What to do now

1. Turn the light off at that switch.
2. If the switch is hot, smells or has marks on it, switch off the lighting circuit at the consumer unit. It is usually labelled lights, and there may be one for each floor.
3. Leave the switch alone. Do not take the plate off to have a look.
4. Use a torch or lamp from a socket in the meantime. Sockets are normally on a different circuit.
5. Arrange for the switch and circuit to be checked.

If you smell burning and cannot tell where it is coming from, switch off the main switch on the consumer unit if you can reach it safely. See our guide to a burning smell from the fuse box for the next steps.

Why loose terminals buzz

Inside a switch, the cables are held under small screws. Over years, heating and cooling as the light is used can slowly loosen them. Plaster movement, a drill nearby or a previous repair can do the same.

When a terminal is loose, the electricity jumps across a tiny gap. That jump is called arcing. It makes a buzz or crackle and produces heat, and heat makes the connection worse. London Fire Brigade names scorch marks and flickering lights among the signs of loose or dangerous wiring.

Dimmers and LED bulbs

Most buzzing dimmers are mismatches. The switch was fitted years ago for filament or halogen bulbs. Then the bulbs were swapped for LEDs to save energy. The dimmer now has very little load to control and starts to hum, and the lights may flicker at low settings.

There are two fixes:

• Fit a dimmer designed for LED loads, sized for the number of bulbs on it.
• Fit LED bulbs that the maker lists as dimmable and compatible with your dimmer type.

If the room also has flicker, our guide to lights flickering in the house covers the bulb and dimmer checks in more detail.

Older switches in Ealing homes

Ealing has a lot of older houses. The VOA’s housing stock figures show that 28% of Ealing homes were built before 1919 and another 30% between 1919 and 1939. That covers the Edwardian streets around Ealing Broadway and Pitshanger, the Brentham Garden Suburb, and the 1930s semis in Greenford, Perivale and Northolt.

In homes like these, it is common to find:

• Metal switch boxes sunk into lime plaster, with old cable entering through a tight hole
• Decorative brass or chrome switch plates that need an earth connection to the plate
• Switches that have been painted over many times, so the plate no longer sits flat
• Dimmers added to a circuit that was wired decades before LEDs existed

None of these is a fault on its own. They are the places we look first when a switch buzzes. If you are in Ealing, it is worth knowing the network there is run by SSEN, not UK Power Networks. That matters if the flicker or buzz affects the whole street. Call 105 and it will route you to the right company.

What an electrician will do

A typical visit for a buzzing switch:

1. Ask what bulbs are fitted and when the noise started.
2. Isolate the circuit and prove it is dead with a tester.
3. Remove the switch and check the terminals, the cable insulation and the back box for heat damage.
4. Check the earth connection, especially on metal plates.
5. Replace the switch or dimmer with one suited to the load.
6. Test the circuit before turning it back on.

If the cable behind the switch is old rubber insulated cable, the electrician should tell you. Electrical Safety First notes that cables coated in black rubber were phased out in the 1960s, and lead or fabric covered cable is even older. Our guide to rubber wiring explains why that matters.

Do I need a certificate?

Replacing a switch like for like is not notifiable under Part P in England. Adding a new circuit is, and so is most work in bathrooms. The Planning Portal’s guidance on electrics explains the rules. Whoever does the work should still test it and can give you a minor works certificate, which is a short record of what was done and tested.

Next step

A humming LED dimmer can wait for a convenient day. A warm, crackling or scorched switch should not. If yours is the second kind, switch off the circuit and request a visit through our lighting faults service. The price is confirmed after a look at the job.