How an electric boiler works
An electric boiler, sometimes called an electric flow boiler, works like a large kettle connected to your central heating. Water from the radiator circuit flows through a chamber containing heating elements. The boiler switches the elements on in stages to reach the temperature you set, and a pump sends the hot water round the radiators, exactly as with a gas boiler. The radiators and pipework can often stay the same when you switch.
Because nothing is burnt, there are no combustion gases to get rid of. Heatrae Sadia describes its Amptec electric boiler as 99.8% efficient for that reason, and the Electric Heating Company describes its Slimjim as 100% efficient. That figure means almost all the electricity turns into heat in your home. It does not mean the heat is cheap, as the running cost section below shows.
Types of electric central heating boiler
- Heating-only flow boilers. Heat the radiators and, with a separate cylinder, the hot water. Heatrae Sadia's Amptec range runs from 4 to 12 kW, and EHC's Slimjim from 4 to 14.4 kW on a single-phase supply. Both makers say a cylinder is needed for hot water.
- Electric combi boilers. Aim to supply heating and hot water from one unit. They either heat water instantly within a limited power budget or include a built-in store. Our guide to the electric combi boiler explains the limits.
- Storage or off-peak models. Heat a large store of water on cheaper night-time electricity and release it during the day. They suit homes on a time-of-use tariff such as Economy 7, but they are bigger and heavier.
Are electric boilers expensive to run?
Yes, compared with gas they usually are. From 1 October to 31 December 2026, Ofgem's price cap sets average direct debit unit rates of 26.32p per kWh for electricity and 7.97p per kWh for gas. An electric boiler turns each unit into almost exactly one unit of heat. A modern condensing gas boiler turns each unit of gas into roughly 0.9 units of heat. Even allowing for that, heat from an electric boiler costs about three times as much.
| Worked example: 10,000 kWh of heat a year | Electric boiler | Gas condensing boiler |
|---|---|---|
| Energy bought | About 10,000 kWh of electricity | About 11,100 kWh of gas (at 90% efficiency) |
| Unit rate (Ofgem cap, Oct to Dec 2026) | 26.32p per kWh | 7.97p per kWh |
| Approximate energy cost | About £2,630 | About £885 |
This is a simple illustration, not a quote. Your own figures depend on how much heat your home needs, your tariff and your region. Price cap rates change every three months, so check Ofgem's latest figures. One point in electric's favour: a home with no gas supply pays no gas standing charge, which on the same cap is 29.68p a day, a little over £100 a year.
A time-of-use tariff can narrow the gap if the boiler stores heat overnight, but for a direct flow boiler that heats on demand, the standard rate is what most homes will pay.
Can an electric boiler heat a whole house?
It can heat a small or well-insulated house, but supply size limits how big a home it can cope with. Most UK homes have a single-phase electricity supply, commonly protected by a main fuse of 60, 80 or 100 amps. At 230 volts, 100 amps is about 23 kW for everything in the house, including the cooker, shower and kettle. A 14.4 kW boiler at full power draws over 60 amps on its own.
That is why single-phase electric boilers top out at around 12 to 15 kW, and why larger or older, draughty homes may struggle. Bigger models need a three-phase supply, which few houses have and which your network operator would have to install. An electrician should check your supply, main fuse and consumer unit before you commit.
Do electric boilers need a flue?
No. An electric boiler burns nothing, so there is no flue, no condensate pipe and no gas pipe. Heatrae Sadia points out that this gives much more freedom over where the boiler goes, which is useful in flats, extensions and loft conversions where a flue would be hard to route. It also means no risk of carbon monoxide from the boiler itself.
Do electric boilers need servicing?
They do not need the annual gas safety check that a gas boiler does, and Heatrae Sadia states there is no requirement for an annual safety certificate on the Amptec. They still benefit from a periodic check by a qualified electrician or heating engineer, looking at the electrical connections, elements, pump, pressure and system water. Sealed systems still have a pressure gauge, expansion vessel and pressure relief valve, just like a gas system. MyBuilder's 2026 price guide puts routine maintenance at around £50 to £100.
Electric boiler cost and installation
MyBuilder's electric boiler price guide, updated in August 2026, gives these typical UK ranges:
| Item | Typical UK cost |
|---|---|
| Standard electric boiler (unit only) | £600 to £2,000 |
| Electric combi boiler (unit only) | £1,500 to £3,000 |
| Electric system boiler (unit only) | £2,000 to £4,500 |
| Basic installation | £500 to £1,500 |
| Electrical circuit upgrade | £200 to £1,000 |
| Consumer unit replacement | £350 to £1,500 |
The same guide puts a full supply and fit at roughly £1,300 to £4,000 for smaller homes, with larger jobs going much higher if extra upgrades are needed. Electric boiler installation is often simpler than gas because there is no flue or gas pipe, but a dedicated high-current circuit is needed. In England, adding a new circuit is notifiable building work under Part P of the Building Regulations, so use an electrician registered with a competent person scheme who can certify it.
Is an electric boiler better than a gas boiler?
It depends on what you have available. If your home has mains gas, a gas boiler is almost always cheaper to run, and a larger home may exceed what a single-phase supply can deliver. If your home has no gas, the comparison changes.
| Electric boilers suit | Electric boilers suit less well |
|---|---|
| Flats where a flue is not allowed or not practical | Larger or poorly insulated houses |
| Small, well-insulated homes with low heat demand | Homes with cheap mains gas already connected |
| Homes without mains gas that do not want oil or LPG | Anyone looking for the lowest running cost |
| Extensions or annexes on their own circuit | Homes with a small main fuse and no upgrade path |
Off the gas grid, it is worth comparing an electric boiler with an oil boiler and with an air source heat pump. A heat pump runs on electricity too but typically delivers around three units of heat for each unit it uses, so its running costs are far lower than an electric boiler's. Heat pumps can also qualify for a Boiler Upgrade Scheme grant of up to £7,500 in England and Wales. They cost more to install and work best with larger radiators and good insulation.
Checks before you choose an electric boiler
- Heat loss. Ask for a room-by-room heat loss calculation so the boiler is sized to the home, not guessed.
- Supply capacity. Ask an electrician to confirm your main fuse size and whether the boiler, shower and cooker can run together.
- Hot water plan. Decide whether you need a cylinder, and where it will go.
- Tariff. Compare a standard tariff with a time-of-use tariff if you are considering a storage model.
Staying safe
An electric boiler runs at mains voltage and high current. Only a qualified electrician should connect it, and only a competent heating engineer should work on the sealed water side. Never remove the cover while the power is on.
If you have gas appliances elsewhere in your home and smell gas, open the windows, turn off the gas at the meter if you can and call the National Gas Emergency Service on 0800 111 999. Any work on gas appliances must be done by a Gas Safe registered engineer.