Why is my plug getting hot?

The three causes of heat at a plug — resistance at a poor connection, an overloaded lead and an undersized adaptor — and why every one of them is a stop-using-it answer.

Difficulty: beginner
Time: 10 min
Read: 4 min
Safety: restricted

Short answer

Heat means resistance where there should be almost none. Either the plug pins are making a poor connection in worn socket contacts, or the terminal screws inside the plug are loose, or the load is too high for the plug, the flex or the adaptor. Switch off, unplug, and do not put it back until you know which. Any discolouration means the socket needs an electrician too.

A healthy plug carrying even 13A should feel no more than mildly warm. Real heat is dissipated power at a bad joint, and a bad joint gets worse: heat raises resistance, higher resistance makes more heat, and the contact degrades further. It is a runaway process and its endpoint is charring inside a wall box.

Safety

A hot plug is a fire warning, not a quirk. Switch the socket off, let it cool, and unplug it. Do not keep using it. If the plug, the pins or the socket face are discoloured, deformed or smell of burnt plastic, isolate that circuit at the consumer unit and get an electrician to inspect the socket before it is used again.

Inside a UK plug and socket, and where the heat comes from

Step by step

Switch off at the socket and unplug once it has cooled.Pulling a hot plug under load can arc. Switch off first, wait, then withdraw it holding the plug body, never the flex.
Look at the pins.Blackening, pitting, blueing or a pin that looks eroded means arcing has been happening. That plug is finished, and so, very likely, is the socket it was in.
Look at the socket face.Browning, a melted lip round a pin hole, or a socket that feels warm even with nothing plugged in. Any of these and the socket is isolated and replaced by an electrician — this is never a clean-and-carry-on.
Work out the load.Read the appliance rating plate. Divide watts by 230 for approximate amps. A 3kW kettle is 13A, right at the plug's limit, and everything about the connection has to be perfect at that current. A 500W lamp getting hot at the plug is a fault, full stop.
Check what it is plugged into.Cube adaptors, unfused two-way adaptors, thin travel adaptors and old block adaptors are a common cause. Many are rated well below 13A total and none of them grip a plug as well as a socket does.
Check the flex where it enters the plug.A flex that is hot only at the plug end suggests the terminals inside. A flex hot along its length suggests it is undersized for the load, which is common with cheap extension leads on heaters.
On a moulded plug, accept that there is nothing to tighten.Moulded plugs cannot be opened. If a moulded plug runs hot and the socket is proven good, the lead is faulty and should be replaced.
Stop using that socket until it has been checked.If the socket shows any sign of heat, put a note on it, isolate the circuit if you can identify it, and get an electrician. Replacing a socket that has arced also means checking the terminals behind it, which is exactly where the damage usually is.

Tips

Heaters, kettles, tumble dryers, washing machines and dishwashers are the loads that expose a marginal connection, because they run near 13A for long periods.
A socket that has had a heater in it for years is worth looking at even if nothing has gone wrong yet — sustained high current wears contacts.
If a plug is hot in one socket and cool in another, the socket is the problem, not the appliance.

Common mistakes

Wiggling the plug to make it work better — That confirms a poor contact and it disturbs an already-degraded connection. If wiggling changes anything, the connection is failing.
Swapping the plug and continuing to use the same socket — The heat is a joint problem and the socket is half of that joint. A new plug into worn, pitted socket contacts will run hot too, and now with less warning.
Treating an adaptor running hot as normal for adaptors — It is common, but it is not normal — it is an adaptor being asked to carry more than its contacts can handle, and adaptor fires are a recognised UK fire-service theme.

If it doesn't work

Plug warm, socket cool, high-power appliance

Cause: Load near the plug's limit, or slightly loose terminals inside a rewireable plug — Fix: If it is a rewireable plug, have the terminals checked by a competent person; if moulded, replace the lead. Do not run a high-power appliance through anything that gets more than mildly warm.

Socket warm with nothing plugged in

Cause: Loose terminal behind the socket, or a failing connection in the fixed wiring — Fix: Isolate the circuit at the consumer unit and call an electrician. This is a genuine fire risk and there is no owner-level check.

Plug pins blackened

Cause: Arcing between pin and socket contact — Fix: Both plug and socket are out of service. Replace the lead and have the socket replaced.

Cube adaptor hot with two appliances in it

Cause: Adaptor rated below the combined load, or poor internal contacts — Fix: Stop using it. Use a fused extension lead of adequate rating, or better, separate sockets.

Extension lead plug hot but individual appliances are fine

Cause: Total load through one plug exceeds what the lead is rated for — Fix: Add the wattages. Keep the total under 3000W and, on a reel, uncoil it fully.

Questions people ask

How warm is too warm?

Mildly warm to the touch on a high-power appliance is normal. Uncomfortable to hold for a few seconds is not, and anything hotter is an immediate stop.

Could it just be a cheap plug?

Counterfeit and very cheap plugs, particularly on imported appliances and USB chargers, are a genuine and documented problem — undersized pins, poor contact material and non-compliant fuses. If a plug looks and feels flimsy, that is a reason to distrust it, but the checks above still apply first.

The socket is fine but the appliance flex is hot — is that a problem?

Yes. A flex should not be noticeably hot. Either it is undersized for the load or a conductor is damaged. Take it out of service.