Electric boilers explained
Heats water with an element rather than a flame. No gas supply, no flue and no annual gas certificate — but a much higher cost per unit of heat.
Hot water
On demand or cylinder
Space needed
Small, wall-hung
Best for
Flats with no gas
Depends on
Electrical supply capacity
The short answer
An electric boiler heats the same radiators and pipes as a gas boiler, using an immersion-style element instead of a burner. Because nothing is burned there is no flue, no condensate and no gas safety inspection, which makes it the practical choice in flats without a gas supply. Every unit of electricity becomes heat, but electricity costs several times more per unit than gas, so running costs are higher for the same warmth.
How it works
A circuit calls for heat
The thermostat or programmer closes the circuit and the element energises in stages rather than all at once.
The element heats the water directly
System water passes over the element inside the boiler and is circulated by the internal pump.
Output is modulated in steps
Most models switch banks of elements in and out to match demand and limit the current drawn.
Hot water comes from a cylinder or a flow model
Larger properties pair the boiler with a cylinder; small flats often use a flow-through model for the taps.
What it needs in the property
A dedicated circuit and enough spare capacity at the consumer unit — often a 40 to 60 A supply.
A main supply fuse able to carry the load. Some properties need an upgrade from the network operator first.
An electrician to certify the circuit; the installation is notifiable work.
A cylinder if the property has more than one bathroom.
The same magnetic filter and system clean as any wet system.
Advantages and trade-offs
Advantages
No flue, so it can go where a gas boiler cannot — internal cupboards, loft conversions, basement flats.
No gas supply and no annual gas safety inspection.
Small, light and quiet, with few moving parts.
Cheaper and quicker to install than a gas boiler.
Every unit drawn becomes heat, with no flue losses at all.
Trade-offs
Electricity costs several times more per unit than gas, so running costs are higher.
Output is limited by the electrical supply, which caps the size of property it can heat.
A supply or fuse board upgrade is sometimes needed, and that adds cost.
Hot water performance from flow-through models is modest.
Scale attacks the element in hard water areas.
Is it right for your home?
Suits
Flats and conversions with no gas supply, small properties with modest heat loss, holiday lets and annexes, and homes where no compliant flue position exists.
Less suitable
Large or poorly insulated houses, and properties with a working gas supply where a gas boiler will cost far less to run.
Sizing it properly
Electric boilers are sized in kilowatts against the heat loss of the property, and the practical ceiling is the electrical supply rather than the appliance. Above about 15 kW the current drawn becomes difficult in a domestic property.
4–6 kW
Studio or one-bed flat, well insulated
8–10 kW
Two-bed flat, six to eight radiators
12–15 kW
Small house, subject to supply capacity
We size from a heat loss calculation and a measured mains flow rate, not from the output of the old boiler.
Book a surveyWhat goes wrong
No heat at all
A tripped breaker, a failed element or a burnt-out contactor. All are traceable at the board and the boiler.
Lukewarm output
One bank of elements has failed while the others still work, so the boiler runs at part output.
Breaker tripping repeatedly
Usually an element breaking down to earth. It needs testing rather than resetting.
Scale build-up
A scaled element runs hot and fails early. Treated system water and a scale reducer extend its life.
Electric boiler questions
Get a fixed price
Send the property details and a photo of the existing boiler and we will quote the whole job in writing, itemised.