Can a Heatwave Cause Power Cuts?

Yes, a heatwave can cause power cuts, and the risk grows the longer the hot spell lasts. Power lines and insulators expand in high temperatures, overheating can reduce the efficiency of network equipment, and lines sag more, bringing them closer to trees, buildings and the ground¹. Hot conditions can also cause underground cables and substations to overheat, which may lead to interruptions². Longer heatwaves mean a higher chance of heat-related faults, which can cause power cuts¹.

The practical answer for a household is to treat a forecast heatwave as a reason to get ready, not to worry. Keep torches, fully charged mobile devices and a battery-powered fan handy, because storms and power cuts can sometimes follow heatwaves². Know that the free number to ring in a power cut is 105, which puts you through to your electricity network operator³. And think now about the two things that matter most in hot weather: keeping cool safely, and keeping food and medicines from spoiling.

This page sets out how the heat strains the network, what to do before a hot spell, how to stay cool and safe if the power goes off, what happens to food, medicines and water, where a generator must never go, and who to call.

How hot weather strains the electricity network

Extreme heat does not only affect people. It can place strains on water and energy utilities, road and rail transport and the health and fire services⁷. For the electricity network specifically, the strain shows up in a few recognisable ways.

Overhead equipment is built for British weather, but heat changes its behaviour. Power lines and insulators expand in high temperatures, and overheating can reduce the efficiency of network equipment¹. As lines expand they sag further, bringing them closer to trees, buildings and the ground, which is where faults begin¹. Below ground, hot conditions can cause underground cables and substations to overheat, which may lead to interruptions². The longer a heatwave runs, the more of this accumulates: longer heatwaves mean a higher chance of heat-related faults, which can cause power cuts¹.

Heat is rarely the only weather in play. Storms and power cuts can sometimes follow heatwaves², and severe weather such as storms, snow, gales, flooding and lightning can all affect the electricity network, damaging equipment and causing power cuts to homes and businesses⁸. Storms can also disrupt power, internet services, transport networks and mobile phone networks⁹. So a summer outage may arrive as a thunderstorm rather than as a still, baking afternoon.

What to do now if a heatwave is forecast

The days before a hot spell are the easy time to prepare. The first thing to sort out is what you would use if the power went off in the heat.

• Light and communications: keep torches and fully charged mobile devices handy, along with a battery-powered fan².
• Cooling without mains power: a battery-powered fan moves air without drawing on the network, and a charged power bank keeps a phone usable if mobile networks hold up.
• Water: water supplies can become depleted in hot weather if people are not prepared¹⁰, and mains water supply to your home could also be disrupted during and after power cuts¹¹. Fill bottles and a vacuum flask in advance.
• Gates and access: make sure electric gates are open before a storm, so you are not trapped or blocking access if the power fails¹².
• Your own health: your health can be affected by hot weather if you are not prepared¹⁰. In a heatwave you may get dehydrated, and your body may overheat¹³.

It also helps to know what will stop working. Internet services, landline phones, heat pumps, electric boilers and some mobile phone networks may not work during a power cut¹⁴. If anyone in the household depends on electrical medical equipment or refrigerated medicines, they are among those most affected, so plan for them first¹⁵.

Keeping cool and safe when the power goes off in hot weather

When the power fails in hot weather, the aim is to keep the home as cool as you can without adding heat, and to keep yourself cool without taking risks.

To reduce heat generated in the home, turn off lights and electrical equipment that are not in use and consider cooking at cooler times of the day¹⁶. Close curtains on the sunny side during the day. If you cannot avoid strenuous outdoor activity like sport, DIY or gardening, keep it for cooler parts of the day like early morning; if you must go out, stay in the shade, wear a hat and light, loose-fitting clothes, preferably cotton, and take plenty of water¹⁷. Wear sunscreen when you are outside¹⁸.

Older people and anyone with a health condition need particular care. Age UK's guidance covers how to stay sun-safe when you are out and about, how to keep your home cooler, and how to spot the warning signs of dehydration and heat exhaustion¹⁹. Learn those signs before the hot spell, not during it.

Food, medicines and water during a summer power cut

A summer cut puts the fridge under pressure faster than a winter one, so it pays to know the rules before you open the door.

The official food safety position is reassuring but conditional: during a power cut, it should be safe to store your food in the fridge as long as it does not rise to 8°C⁵. Keep the door closed as much as possible, and use a fridge thermometer if you have one. If the temperature climbs past that point, treat the contents with caution. Power cuts are common during adverse weather events, and electrical items such as fridges, freezers and ovens may break down if they have come into contact with water²¹, so check appliances after any flooding that follows a storm.

For medicines, do not improvise. In the event of a power cut or fridge breakdown, contact your local pharmacy or the manufacturer of your medication for further information on what to do²². People who rely on electrical medical equipment or refrigerated medicines are among those for whom a cut has the greatest impact¹⁵. If that is your household, work out the plan in advance and keep the pharmacy number with your emergency numbers.

Where a generator must never go in hot weather

The rule does not change with the season. Never use standby generators indoors, as the fumes from the engine can be lethal⁶. That applies in a heatwave exactly as it does in a storm, and it applies to garages, sheds, conservatories and any space attached to the house where exhaust can build up.

The same principle covers other heat sources people reach for when the power fails. Never use outdoor heaters indoors²³. Keep heaters away from curtains and furniture and never use them for drying clothes²⁰. Never use portable gas cylinder heaters in high rise flats²⁰.

Wildfire risk near homes in hot, dry weather

A heatwave dries the ground and the vegetation around it, and that raises the risk of fire close to where people live. One small spark can quickly spread into a blaze that threatens the countryside, habitats, homes and infrastructure, particularly during warm, dry weather²⁴. The wider effects of a severe heatwave include vulnerable members of the public struggling to keep cool and becoming seriously ill, widespread wildfires, melting of roads, buckling railway lines, droughts, dehydration and sunburn²⁵.

There are practical things a household can do. Cutting back trees and shrubs that are close to or touching your house and disposing of the waste responsibly reduces the fuel available to a fire²⁶. Keep the area around the home clear, and be careful with anything that can throw a spark outdoors in dry conditions.

If you see a fire, do not approach it. Report it and move away. Wildfire spreads faster than people expect, and the smoke alone can be harmful.

Who to call in a power cut: 105 and your network operator

If the power goes off, the first number to know is 105. The electricity network operators have introduced 105 to give you an easy-to-remember number to call that will put you through to your network operator²⁷. Calls are free⁴. If you are unsure who to call, or in the event of a power cut, call 105⁴.

You can also report it directly to your local network operator using their website, or call 105 for free³. For an electrical hazard or power cut, contact your local electricity company or call 105⁴. Power cut? Contact your local network operator online or call 105, the free power cut emergency number²⁸.

Before you ring, do one quick check. Check to see if your neighbours are safe and if they have a power cut too; if they have power, your trip switch may have activated²⁹. That single question tells you whether the fault is yours or the network's.

Getting help and checking on each other

Some households need more support than others, and the system has a way to record that. Sign up to your energy supplier's Priority Services Register to let them know that you need additional support during a power cut¹¹. It is the single most useful thing a vulnerable household can do before a hot spell.

Neighbours matter too. Check up on relatives or neighbours who might need help during a power cut³⁰. For anyone vulnerable, make sure they are warm, their medical equipment is working, and they have enough food and drink³¹. In a heatwave, add water and shade to that list.

If you are worried about someone's health in the heat, Age UK's guidance on spotting the warning signs of dehydration and heat exhaustion is a good place to start¹⁹. And if a cut lasts, your network operator can tell you what is happening and when power is expected back.