An electric combi boiler combines central heating and instant domestic hot water in a single wall-mounted unit — with no need for a flue, gas supply, or separate hot water cylinder. They're quiet, compact, 100% efficient at point of use, and ideal for flats, apartments, smaller homes, or any property where gas isn't available or practical.
Browse our range from trusted brands including EHC, Strom, Biasi, Elterm, EHS, E.C.A, and ThermoSphere — all available in a range of power outputs to suit different property sizes and electrical supplies.
Choosing the Right Power Output — This Matters More Than You Think
One of the most common mistakes when buying an electric combi boiler is underestimating how much power is needed for a satisfying hot water experience. The kW rating does two jobs simultaneously: heating your radiators and producing instant hot water on demand. When you open a hot tap or turn on a shower, the boiler switches to domestic hot water (DHW) mode and uses its full rated power to heat the water as it flows through.
The amount of hot water an electric combi can produce depends entirely on its kW output and your incoming cold water temperature. As a rough guide, assuming a cold water inlet temperature of around 10°C and a desired output of 45°C (a ΔT of 35°C):
7kW produces approximately 2.9 litres per minute of hot water. This is a common source of frustration — many buyers choose a 7kW boiler expecting a decent shower and are disappointed. A standard shower typically needs at least 6–8 litres per minute, meaning a 7kW boiler on its own is unlikely to deliver a satisfying showering experience unless you're using a very low-flow showerhead or a thermostatic mixer set to a relatively low temperature. A 7kW boiler is better suited to properties where hot water demand is very low, such as a single-person flat with a bath or a system used primarily for central heating with minimal hot water draw.
11kW produces approximately 4.5 litres per minute — an improvement, but still marginal for a standard shower. Better suited to smaller homes with modest hot water demand.
14kW produces approximately 5.7 litres per minute — generally considered the practical minimum for a comfortable single shower and is the most popular choice for a typical 2–3 bedroom home.
18kW, 21kW, and 24kW+ (three phase) are suited to larger homes, multiple bathrooms, or higher simultaneous hot water demand.
If your primary concern is hot water delivery rather than just heating, you may also want to consider models like the Elterm Ensign range, which separates the central heating and DHW kW ratings — allowing a higher output for hot water independently of the heating circuit.
⚠️ Important: Check Your Electrical Supply Before Ordering
Electric combi boilers are high-draw appliances. Unlike a gas boiler that just needs a fused spur, an electric combi needs a dedicated circuit from your consumer unit, sized correctly for its rated power. Here's what that means in practice:
A 7kW boiler on a 230V single-phase supply draws approximately 30 amps — typically wired on a 6mm² cable with a 32A or 40A MCB.
A 14kW boiler draws approximately 61 amps — requiring a dedicated 10mm² cable and a 63A or 80A MCB. This is a significant load, and your installer will need to confirm your consumer unit can accommodate an additional circuit of this size alongside your other loads. Most standard UK homes have a 100A main fuse, which can handle a 14kW boiler, but it's important your installer assesses the total connected load.
If your property cannot support a 14kW single-phase supply, you have two options: choose a lower output model, or upgrade to a three-phase supply (if available), which spreads the load across three phases and makes higher outputs like 18kW, 21kW, or 24kW far more manageable electrically.
All electric boiler installations in the UK must be carried out by a qualified electrician and may require notification to your local building control authority under Part P of the Building Regulations.
Why Choose an Electric Combi Boiler?
Electric combi boilers are a practical, future-proof choice for properties moving away from fossil fuels. Key advantages include no flue or gas pipe required, 100% on-site energy efficiency, extremely low maintenance (no annual gas servicing), compatibility with renewable energy sources like solar PV, and eligibility for off-peak tariffs such as Economy 7 or Agile Octopus when combined with smart controls. They're also ideal for off-grid properties, new builds, conversions, and flats in multi-occupancy buildings.
Browse our full range of electric combi boilers below — or contact our team for help sizing the right model for your home.
