Power cut guide
Boilers, Heat Pumps and Heating After a Power Cut
Quick answer: Almost every modern gas or oil boiler needs electricity for its controls, ignition, fan and pump, so your central heating stops in a power cut even though the gas is still on. When the power comes back, most boilers and heat pumps restart by themselves, but some need a simple reset from the control panel and timers often need setting again. If a boiler won’t restart or you smell gas, don’t take anything apart: call a Gas Safe registered engineer, or the gas emergency line on 0800 111 999 if you smell gas.
Is the power off where you are? See live power cuts from the network operators and reports from neighbours.
This guide is for anyone who has just had the heating go off with the lights, or wants to know what to expect before winter. It covers gas combi and system boilers, heat pumps, electric storage heaters and hot water cylinders, and explains what you can safely check yourself and what must be left to a professional.
Why your gas boiler stops when the electricity goes off
It surprises a lot of people that a gas boiler goes cold in a power cut. The gas supply itself usually keeps flowing, but the boiler can’t use it without electricity.
A typical modern boiler relies on mains power for several jobs at once:
- Ignition. The clicking you hear when the boiler fires up is an electric igniter lighting the gas. No power, no spark.
- The flue fan. This pushes waste gases out through the flue. The boiler’s circuit board checks the fan is working before it will light, as a safety measure.
- The circulation pump. This moves hot water around your radiators. Without it, the heat stays in the boiler.
- Controls and thermostats. Display screens, timers, room thermostats and smart thermostats all need power, and wireless thermostats often talk to a receiver that is mains powered.
So whether you have a combi, a system boiler or an older regular boiler with a tank in the loft, the answer is the same: if the house has no electricity, the central heating won’t run. The same goes for most oil and LPG boilers, which also use electric pumps, fans and controls.
If you want to keep warm while you wait, our guide to keeping warm in a winter power cut covers layering, closing off rooms and safe ways to heat one space.
Safety: Never try to bypass a boiler’s controls, wire it to a battery yourself, or open the casing to “get it going”. Work on gas appliances must be done by a Gas Safe registered engineer. Unsafe gas work can cause leaks, fires and carbon monoxide poisoning.
How different heating systems behave in a power cut
Not every system reacts in the same way. This table gives a general picture. Your own manual is the final word for your model.
| Heating type | During the power cut | When power returns |
|---|---|---|
| Gas combi boiler | Stops. No heating and no hot water from the taps. | Usually restarts. Some show a fault code and need a reset. Check the timer. |
| Gas system or regular boiler with cylinder | Stops. Water already in the cylinder stays hot for a while. | Usually restarts. Check the boiler timer and any immersion heater timer. |
| Oil or LPG boiler | Stops, as pumps, fans and controls need power. | Usually restarts. Some models have a lockout or reset button; follow the manual. |
| Air source or ground source heat pump | Stops. | Normally comes back on by itself, but may need time to warm up after a long cut. |
| Electric storage heaters | Keep giving out heat already stored, but can’t recharge. | Recharge in the next off-peak period. Check heater and immersion clocks. |
| Electric panel heaters or electric boiler | Stop straight away. | Usually come back on. Check thermostats and timers. |
Hot water during a power cut
A combi boiler heats water on demand, so when it stops, the hot taps run cold almost straight away. You’ll still have cold water from the mains in most homes, because mains water pressure doesn’t depend on your electricity.
If you have a hot water cylinder (usually in an airing cupboard), the water already heated stays warm for some hours, more if the cylinder is well insulated. Use it sparingly for washing rather than running a full bath. Showers are different: an electric shower won’t work at all, and a pumped or “power” shower needs electricity for its pump.
Some homes with a cylinder also have an immersion heater as a backup. That’s electric too, so it won’t help until the power is back.
Getting a gas boiler going again when the power returns
In most cases you don’t need to do anything. The boiler sees power return, runs its own safety checks and fires up when the timer or thermostat calls for heat. Give it a few minutes before assuming there’s a problem.
If the heating still isn’t working, go through these checks in order:
- Is the power fully back? Check that lights and sockets work. If only some things have come back, look at your fuse box in case a trip switch went off when the supply returned.
- Check the boiler’s fused spur. Most boilers are wired to a switched fused connection unit on the wall nearby. Make sure it’s switched on.
- Check the clock and timer. Many boiler timers and programmers lose their setting in a power cut, so the heating may be “off” according to the clock. Set the correct time and check the on/off periods.
- Check the room thermostat. Some need their schedule re-entering or batteries replacing. A smart thermostat may need a few minutes to reconnect to your Wi-Fi.
- Look at the display. If the boiler shows a fault code or a flashing light, look it up in the user manual. Many manufacturers publish manuals and fault code lists on their websites.
- Use the reset function, if the manual says so. Most boilers have a reset button or a reset option in the menu. The manual will tell you when a user reset is appropriate and how many times to try.
- Check the pressure gauge on sealed systems. If the manual gives a normal range and the needle is outside it, follow the manual or call an engineer.
This is a general list rather than step-by-step instructions for any brand. Buttons, menus and codes differ between manufacturers and models, so always follow the instructions for your own boiler.
What “lockout” means
Boilers are designed to shut themselves down safely if something isn’t right, for example if the flame doesn’t light properly or the fan doesn’t respond. This safety shutdown is often called a lockout, and the display usually shows a code. A one-off lockout after a power cut can sometimes be cleared with a single user reset. If the boiler keeps locking out, it’s telling you there’s a fault that needs an engineer.
In very cold weather, a frozen condensate pipe (the plastic pipe that carries waste water from a condensing boiler outside) is a common reason for a boiler not firing. Some manufacturers publish advice on safely thawing it. If you’re not confident, call a heating engineer.
Tip: Find your boiler’s make and model now, while everything is working, and save the user manual as a PDF on your phone. In a power cut it’s much easier to read a fault code list you already have than to search for one on a low battery.
When to stop and call a Gas Safe engineer
Resetting a boiler from its control panel, as the manual describes, is fine. Anything beyond that is a job for a professional. Call a Gas Safe registered engineer if:
- the boiler locks out again after one or two resets;
- you see water leaking, scorch marks or soot around the boiler;
- the flame looks lazy, yellow or orange instead of crisp and blue (on boilers where you can see it);
- you hear unusual banging, whistling or gurgling that wasn’t there before;
- your carbon monoxide alarm goes off, or anyone has headaches, dizziness, nausea or breathlessness that ease when they go outside.
You can check an engineer is on the Gas Safe Register by asking to see their ID card and checking it on the Gas Safe Register website. If you rent, tell your landlord or letting agent, who is responsible for gas safety in the property.
If you smell gas
A power cut doesn’t usually affect your gas supply, but if you notice a smell of gas at any time:
- call the gas emergency line on 0800 111 999 (Great Britain, free, 24 hours) or 0800 002 001 in Northern Ireland;
- open doors and windows;
- turn off the gas at the meter if you can safely reach it;
- don’t switch lights or appliances on or off, and don’t use anything that could make a spark;
- don’t smoke or light a flame;
- leave the property if you feel unwell and wait for the all-clear.
If anyone has symptoms of carbon monoxide poisoning or the situation is life-threatening, call 999. All the key numbers are on our emergency numbers page.
Safety: Don’t use a gas cooker or oven to heat a room, and never bring a barbecue, camping stove, patio heater or generator indoors. They all produce carbon monoxide, which you can’t see or smell.
Heat pumps after a power cut
An air source or ground source heat pump runs entirely on electricity, so it switches off as soon as the power goes. The good news is that most systems are designed to come back on by themselves once power returns, with their settings intact.
After a long power cut, a heat pump may need time to bring the water in the system back up to temperature before your radiators or underfloor heating feel warm again. Depending on the system, this may happen automatically or you may need to choose a setting. Some manufacturers suggest a gradual restart after a long outage, for example heating the hot water cylinder first, then opening radiators a few at a time. Check your own heat pump’s manual or ask your installer what they recommend.
Things worth checking once the power is back:
- the controller or thermostat shows the right time and schedule;
- there are no fault messages on the indoor unit or controller;
- the outdoor unit isn’t blocked by snow, ice or storm debris (keep clear of the fan and don’t poke anything into the unit);
- any isolator switch near the outdoor unit is on.
If the heat pump shows an error that doesn’t clear, contact your installer or the manufacturer’s support line rather than opening any panels.
If you have solar panels as well, it’s worth knowing that ordinary grid-tied solar switches off in a power cut for safety. Our guide to solar panels and home batteries in a power cut explains which systems can keep some circuits running.
Storage heaters and immersion heaters
Electric storage heaters are designed for off-peak tariffs such as Economy 7. They soak up heat during cheaper overnight hours and release it through the day. The input dial controls how much heat is stored; the output dial controls how quickly it’s given out.
That gives them one advantage in a power cut: heat already stored in the bricks keeps coming out for a while. To make it last:
- turn the output dial down so the heat is released slowly;
- keep doors to heated rooms closed;
- draw curtains once it gets dark.
The catch is that if the power is off overnight, the heaters can’t charge, and you may have little stored heat the following day. They’ll charge again during the next off-peak period after power returns.
Afterwards, check the clocks on your storage heaters and any immersion heater timer, as some may have lost their time. Many modern storage heaters have a battery that keeps the clock running, but older ones and mechanical immersion timers may need resetting. If you’re unsure of your off-peak hours, your supplier can tell you.
Keeping some heating going with backup power
People often ask whether they can run a gas boiler from a portable power station or generator. Technically, a boiler’s electrical load is fairly small compared with an electric heater, but connecting one safely is not a DIY job.
- A boiler is usually hard-wired through a fused spur, not plugged in. Changing that wiring needs a qualified electrician, and the boiler manufacturer may have requirements about the power supply.
- A generator must never be connected to your house wiring except through a changeover switch fitted by a qualified electrician. Back-feeding the network can kill engineers working on the lines.
- Generators must only ever be run outdoors, well away from doors and windows.
If you want to look into backup power for heating, start with a qualified electrician and your boiler or heat pump installer. Our guide to choosing a portable power station explains what these units can and can’t realistically run.
Frequently asked questions
Does a combi boiler work in a power cut?
No. A combi boiler needs electricity for its ignition, fan, pump and controls, so you’ll have no heating and no hot water until the power returns. The gas supply itself is normally unaffected.
Why won’t my boiler come back on after a power cut?
The most common reasons are a timer or programmer that has lost its setting, a thermostat that needs resetting, or a safety lockout. Check the clock first, then look up any fault code in your manual and use the reset function if the manual says to. If it keeps locking out, call a Gas Safe registered engineer.
Is it safe to reset my boiler myself?
Pressing the reset button or using the reset menu, as described in your user manual, is designed for householders to do. Opening the casing, adjusting gas parts or rewiring the boiler is not. Leave those jobs to a Gas Safe registered engineer.
Will my heat pump restart on its own?
Most heat pumps come back on automatically when the power returns. After a long cut, the system may take a while to warm up again. If it shows an error or doesn’t start, check the manual and contact your installer.
Do storage heaters lose their heat in a power cut?
They keep releasing the heat they’ve already stored, so turn the output down to make it last. They can’t recharge until power returns and the next off-peak period comes round.
For a full run-through of what else to check once the lights come on, from fridges to fuse boxes, read what to check when the power comes back on. If you’re still waiting, check your postcode for the latest estimated restoration time. If someone in your home is older, very young or relies on warmth for their health, think about joining the Priority Services Register so your network operator knows to keep you updated.
Sources
- Viessmann u2013 Does a boiler need electricity?
- West Midlands Combined Authority u2013 Heat pump turns off
- Baxi u2013 How to restart your air source heat pump after a power cut
- Citizens Advice u2013 Using storage heaters and immersion heaters
- Cadent u2013 What to do if you smell gas
- Cadent u2013 Gas safety advice
Checked against these sources on 28 October 2026. Rules and amounts can change – your network operator or Ofgem has the final word. Spotted something out of date? Tell us.
More on home, food and health: The Priority Services Register Explained · All power cut guides