Why does my plug fall out of the socket?

How to tell a worn socket from a worn plug in thirty seconds, what a loose grip actually means electrically, and why it is a replace rather than a fix.

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

Short answer

Try a different plug in the same socket, and the same plug in a different socket. If every plug is loose in that one socket, the socket's contacts are worn and the socket needs replacing. If one plug is loose everywhere, that plug or lead is worn. Either way it is a replacement, because loose contacts arc and arcing burns.

A BS 1363 socket grips by spring pressure on the pins. That spring is a piece of shaped metal that gradually loses tension through thousands of insertions, through heat, and through being used with slightly undersized counterfeit pins. Once it has lost tension, the contact area shrinks, resistance rises, and heat begins the cycle described in the hot-plug guide.

Safety

A plug that no longer grips is a plug that can arc, and arcing at socket contacts is a fire cause. Do not push it back and carry on. Isolate the circuit and have the socket replaced if the socket is at fault — a worn socket is not repairable and there is no owner-level way to tighten the internal contacts.

Step by step

Do the two-way swap test.Take a plug you know is fine and try it in the suspect socket. Then take the suspect plug to a socket you know is fine. Thirty seconds and you have isolated which half is worn.
Look at the socket face with the plug out.With the socket switched off, look at the pin holes. Splayed, discoloured or asymmetrical openings, or a shutter that no longer closes when the plug is removed, all say the socket is finished.
Look at the plug pins.Pins should be square-edged and unmarked. Rounded, scratched, blackened or visibly thinner pins mean the plug is worn or was never to specification. Counterfeit plugs with undersized pins are a common cause of "my new appliance falls out of every socket".
Check whether the socket moves in the wall.A socket whose back box has come loose rocks when a plug is pushed in. That strains the terminations behind, which is the more serious version of this problem. It needs the accessory removed and the box refixed, which is a job for someone competent to isolate and prove dead.
Take it out of service if it is the socket.A socket with worn contacts is not adjustable and not repairable. Stop using it, and get it replaced. Replacing a socket faceplate is a like-for-like swap in an ordinary room, but the wear is usually accompanied by heat at the terminals, which is why an electrician looking behind it is the safer route.
Replace the lead if it is the plug.On a moulded plug, the lead is replaced. On a rewireable plug, replacing the plug is straightforward, but check the flex and the cord grip while you are there.
Check for heat damage before reusing anything.Any browning on the socket face, any smell, or any warmth means this has been going on long enough to damage the accessory and possibly the terminations behind it. Isolate the circuit and get it inspected.

Tips

Sockets behind furniture that are plugged and unplugged constantly — vacuum cleaners, chargers — wear fastest. They are also the ones nobody looks at.
A small spark as a plug is pushed into a live socket carrying a switched-on load is normal contact arcing. A visible flash, a repeated crackle, or a spark with nothing switched on is not.
If a socket has a switch, switching off before plugging and unplugging genuinely extends its life, because the contact is made without current flowing.

Common mistakes

Bending the plug pins outward to make it grip — It temporarily increases pressure at one point and permanently damages both the plug and the socket contacts. It also puts the pins out of specification so the plug then damages every other socket it goes into.
Propping a loose plug in place with tape or a wedge — It keeps a poor contact under load rather than removing it. The heat and the arcing continue, out of sight and now unmonitored.
Assuming a loose socket is just cosmetic — Grip and electrical contact are the same thing in a BS 1363 socket. Loose grip is literally reduced contact area, which is literally increased resistance.

If it doesn't work

Every plug loose in one socket

Cause: Worn socket contacts — Fix: Stop using it and replace the socket. Have the terminations behind checked at the same time.

One plug loose in every socket

Cause: Worn or non-compliant plug pins — Fix: Replace the lead or the plug. Check the appliance's plug is BS 1363 marked.

Socket rocks in the wall

Cause: Back box loose, or plasterboard box lugs failed — Fix: Isolate the circuit and have the box refixed. A rocking socket strains and eventually loosens the terminals behind it.

Socket face browning around one pin hole

Cause: Sustained arcing at that contact — Fix: Isolate the circuit at the consumer unit and call an electrician. This is heat damage, not dirt.

Crackling or a visible flash when plugging in

Cause: Arcing on a degraded contact — Fix: Stop using that socket immediately and have it replaced.

Questions people ask

Can I just tighten it up?

No. There is no adjustment. The contacts are spring metal inside a moulding and once they have relaxed, the accessory is at end of life.

Are shuttered sockets more prone to this?

All UK sockets are shuttered by design — the earth pin opens the live and neutral shutters. A shutter that no longer springs closed is a separate defect and also means replacement.

Is it worth replacing all the sockets in an old house?

Not as a blanket exercise. Replace the ones that are worn, damaged or discoloured. If several are failing, that is a good prompt for an EICR, which will look at the whole installation rather than one accessory at a time.