Can I open the board to see where it is coming from?

You should not. With the cover off you have live parts within reach, and if there is a glowing point the extra air can feed it. Looking tells you nothing we will not see in a minute with the right instruments.

What if the smell comes from a socket, not the board?

The treatment is the same. Unplug whatever was connected, switch off that circuit's breaker if you know which it is, and stop using that outlet. The mechanism — resistance, heat, degradation — is identical; only the location changes.

How often should board terminals be checked?

An inspection with re-torquing and thermography every few years prevents almost all of these cases, and it is particularly worthwhile on the coast, where salt accelerates contact corrosion.

Is it more common in older installations?

Yes, for two reasons that compound. Boards from the seventies and eighties were built for far lower consumption than today's, and their terminals have had decades of heating and cooling cycles loosening the joint. Adding air conditioning or an induction hob to an installation of that era is the classic scenario.

Burning smell from the consumer unit

This is the one fault that allows no waiting and no experimenting. If there is smoke, flame, or a strong smell: main switch off if you can, out of the property, and call 112. Do not go back in for belongings.

Right now

1Switch off the main isolatorThat is the only thing you should touch. If reaching the board means putting your face close to it, or you can see smoke, do not even do that — leave.
2Do not open the board coverOpening it feeds oxygen to a point that is already hot and puts your hands centimetres from live parts.
3Ventilate and get outOpen a window on your way past and leave the property. Burning PVC fumes are toxic long before there is any visible flame.
4Call 112 if there is smoke or flameWith visible smoke this is a fire-service emergency, not an electrician's. We come afterwards, once it is under control.

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Why it happens

A loose terminal in the board

The dominant cause. An under-tightened screw creates resistance, resistance creates heat, and heat loosens the screw further. It takes weeks, and the sour smell of the plastic is the first external sign.

A degraded breaker or RCD

Internal contacts pit after many operations and begin to heat under normal load. It shows up on a thermal camera, not to the naked eye.

An overloaded extension lead or socket

Very common behind a TV unit or under a worktop. The smell comes from the socket rather than the board, but the mechanism is identical.

Undersized cable after refurbishment

A circuit extended without checking conductor size runs permanently at its limit. It heats along its whole length rather than at one point, and that is its distinguishing sign.

What we do on arrival

We inspect the board with a thermal camera under load — the only way to see a hot spot before it announces itself.
We re-torque every terminal with a torque screwdriver to the manufacturer's figure, not "firmly by hand".
We replace the affected device or cable run; a terminal that has already charred the plastic is not recovered by re-tightening.
We check whether the circuit was overloaded, because if that was the cause, fixing the point without fixing the load only postpones it.

Frequently Asked Questions

No. The smell appears once the insulation is already degrading from heat, and that process does not stop on its own. Switch off the main isolator and call the same day, even at night: it is the only fault on this list where waiting changes the outcome.