Power cut: what happens to your boiler, hot water, Wi-Fi and phone

The short answer

GOV.UK's Be Ready campaign puts it plainly: gas ovens, boilers, heat pumps and your home internet won't work without power. Mains water can be disrupted during and after power cuts too.

The gas itself doesn't go off. What stops is the electricity your boiler needs to run.

Heating and hot water, by type

Be Ready confirms boilers and heat pumps stop. The details on hot water and storage heaters below are general information about how these systems work, not from an official source. Check your own system's manual.

If you use a fire or stove, have a working carbon monoxide alarm. The NHS lists wood, gas and coal fires among the things that can give off carbon monoxide, a gas you can't see or smell.

Keeping warm until it's back

The SSEN network says heat can drop quickly in a power cut, and suggests dressing warmly and staying active. Practical steps:

• Close curtains and internal doors, and stay in one room.
• Layers, hats, blankets and sleeping bags. A hot drink from a flask filled earlier.
• Never use a gas oven, a camping stove, a barbecue or a generator indoors to keep warm. The NHS lists portable generators, camping stoves and indoor barbecues as causes of carbon monoxide build-up.

Our post on keeping warm without power has the full list.

When the power comes back

• Your boiler should restart by itself. If the clock or timer has reset, set it again.
• If it doesn't fire up, check the manual for a reset button. If that doesn't work, call the maker or a Gas Safe registered engineer. Don't take the casing off.
• Smart thermostats may need a few minutes to reconnect to Wi-Fi.
• Storage heaters recharge on the next cheap-rate period.
• SSEN suggests leaving one light on so you know when the power is back.

Wi-Fi and internet

Be Ready says you'd lose your internet connection in a power cut. That's because:

• your router needs mains power;
• if you have full fibre, the small box where the fibre comes into your home (often called an ONT) needs power too.

Mobile data may keep working for a while. Be Ready says your mobile might stop working if your local mast is in the affected area, though some masts have back-up power. A government page for phone and broadband companies says they should bring generators to masts wherever possible, but that doesn't mean every mast stays on.

To keep some internet:

• Keep your phone charged and turn on its hotspot if mobile data works.
• A power station with a normal socket can run a router and fibre box. Our runtime calculator shows roughly how long.
• Some routers can run from a power bank, but many need a higher voltage than USB gives. Check the label on your router's plug before buying anything. (General information, not from an official source.)

Landline phones

Ofcom says digital landlines need mains electricity and won't work in a power cut unless there's a battery back-up.

• If you depend on your landline (for example, no mobile or no reliable signal), your provider must offer a free back-up, such as a battery unit, that lasts at least one hour. Ofcom says some last up to seven hours.
• Be Ready says an old-style corded landline may still work if you're still on an analogue line.
• If you have a telecare alarm that uses your phone line, the government page tells people to ask their provider whether it will work in a power cut.

Our post on digital landlines in a power cut covers this in more detail.

Calling 999

Ofcom says a 999 call from a mobile can connect through another network if yours has no signal. The government's telecoms page says that if 999 doesn't connect from a mobile, try 112, or move outdoors or to higher ground for a better signal.

Fridge and freezer

They stop too. The Food Standards Agency says a fridge should stay cold for up to 4 hours, and a full freezer should stay frozen for up to 48 hours (24 hours if half full), as long as you keep the doors shut. Our fridge and freezer timer counts it for you.

Before the next power cut

1. Know 105: the free number to report or check a power cut in England, Scotland and Wales (Be Ready).
2. Put warm layers, a torch and a charged power bank where you can find them in the dark.
3. Check whether your landline is digital, and ask your provider about a battery back-up if you rely on it.
4. If anyone at home relies on powered medical equipment, join the Priority Services Register.

What we couldn't check

• We couldn't open boiler makers' pages or the Gas Safe Register (bot checks), so restart advice is general. Your boiler's manual is the best guide.
• The Energy Saving Trust page on hot water cylinders blocked our checks, so the cylinder and storage heater rows are general information.

Related guides

• Power cuts in the UK: what to do
• Keeping warm without heating: what works, what's safe, and where to get help
• Broadband and phone outages: what to do, and how to prepare
• Winter power cut checklist for UK homes
• Priority Services Register: a plain guide

Free tools

• Power cuts near me
• Power bank and power station runtime calculator
• Fridge and freezer power cut timer (FSA times)

We're an independent UK site, not the government. We check guides against official sources and link to them. In an emergency call 999.

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