Electric Combi Boilers – 6kW to 48kW Outputs

Electric Combi Boilers or Electric Combination Boilers as they should really be referred too, are electric boilers that will do both your heating and your Domestic Hot Water requirements. They are a great solution for properties or households that have no access to natural gas or where oil or LPG is not practical.With advancements in technology, electric combi boilers have evolved into a  advanced and competitive product,mainly due to they are typically easier to maintain and install than gas boilers, and are extremely quiet in operation.Some of the benefits of electric combi boilers are that they are small and compact , so can often fit in a cupboard in the kitchen for example , or under the stairs etc . The other huge benefit is that they require no flue pipe, unlike a gas or oil boiler as they don’t release any gases into the environment, so the risk of CO2 poisoning from a faulty flue or boiler are eliminated, this means that you can locate your electric combi boiler in more locations to suit your needs, rather than having to position it accommodate the flue system and regulations that you have with gas or oil boilers.

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Electric Combi or Combination Boilers from 6kW to 48kW from Flexiheat UK

Electric combi boilers come in a variety of outputs and the most suitable option for your property or home will depend not only on your heating requirement but mainly on your hot water usage and the number of bathrooms you have.None of our electric combi boilers emit gases or direct pollution when operating and do not operate using fuels such as gas or diesel and therefore no risk of leaks or explosions.All of our electric combination boilers are highly efficient at 99% , and come with a LCD control panel , that allows you to have 3 daily programmes ( i.e. on/off periods ) , and are fitted with the latest ErP low energy rated heating pumps.Our Electric combi boilers also feature –

  • Fully modulating operation in 3 steps – i.e. 1/3rd power ,2/3rds power or full power output
  • Can be used with solar heating systems
  • A Frost protection system – If the temperature of water inside the boiler is under 5 Degrees C, pump and heating elements will operate to bringing the water temperature up to the security level of 35 Degrees C
  • Instant and constant hot water temperature via a plate heat exchanger
  • Overheat protection system
  • Can be used with a wet underfloor heating system
  • Can be used on a a traditional central heating system with radiators
  • Three levels of output settings i.e. The boilers can be set to 1/3rd , 2/3rds or 3/3rds of their maximum kW output – giving you maximum control your electric combi boiler
  • Option to set the temperature individually for each separate heating programme
  • Anti – Block Function -The pump and 3 way valve inside the electric combi boiler operate once every 18 hrs to ensure that there will be no blockage within the boiler
  • Can utilise either Single Phase ( 220 volt ) or Three Phase ( 400 volt ) as their power supply – depending on the electric combi boilers output


Are electric combination boilers the right choice for you and your home or flat ?

This is one of the most important questions to ask yourself , because there are limitations for electric combi boilers,and here is why –

  1. Unlike a gas fired combi boiler, whereby you can get a relative high amount of energy down a small diameter pipe, with electricity, the higher the power required – the large the diameter cable you require , and more importantly after 15kW in Output you in reality have to jump from Single Phase 240 Volt ( which is the standard household domestic supply ) to Three Phase 415 Volt – which is normally the industrial electrical supply, as it can handle more Amp’s.
  2. Why does this change in Voltage matter ? Well it matters because most domestic properties in the UK have only 240 Volt  Single phase electrical supply to them , that have a 100 Amp Fuse Board / Consumer Unit ( there are some very old properties which may have only a 60 Amp supply, but this is very rare now – but it’s worth checking ). Which means that all the home electrical appliances , whilst being used simultaneously should not draw over 100 Amps , otherwise the fuse can blow, and out your electric.
  3. Following are some typical electrical loads for common household electrical appliances –
    Domestic Electric ApplianceAmps UsedWatts Used
    Laptop<0.565 – 100
    Mobile phone charger<0.5<12
    Satellite TV box<0.530
    DVD player<0.528
    Hair dryer10.02200
    Landline cordless telephone charger<0.510
    Computer monitor<0.5100
    Desktop computer3.0700
    Television 42″ HD0.5120
    Games console0.86<200
    Washing machine102200
    Tumble dryer11.02500
    Vacuum cleaner9.02000
    Radiator (oil filled)13.03000

4. Ok, now for the electrical consumption of our Single Phase 240 volt Electric Combi Boilers –

240 volt – Single Phase Electrical Combi Boilers – Electrical Consumption – With Fuse and Cable requirements

ModelOutput in kWDraw Current- AmpsFused & Residual Current Device- AmpsCable Section
EDM10101* 45.51* 503*6
EDM12121* 54.61* 633*10
EDM16161* 72.81* 803*16
EDM18181* 81.91* 1003*16

So as you can see see from the above table, if you are running a 16kW electric combi boiler , which will draw 72.8 Amps of electrical power on a single phase supply , and you have a hair dryer on at 10 amps, plus a dishwasher at 10 amps , then someone pops the toaster on at 9 amps , your going to end up with a demand of 101.8 Amps , which will probably mean your fuse blowing. Now to be fair to this statement, there are a few factors to consider –

  • The “diversity factor” – which is defined  as the (unofficial) term diversity in relation to electrics, refers to the percent of time available that a machine, piece of equipment, or facility has its maximum or nominal load or demand (a 70% diversity means that the device in question operates at its nominal or maximum load level 70% of the time that it is connected and turned on).
  • Is this potential situation applicable to your circumstances – If you live in a flat , or smaller house , with either one or two occupants , are you like to see this scenario ?e.g. if there’s only one occupant –  If your in the shower , then you can’t be putting a toaster on at the same time  ? or using a hair dryer at the same time.
  • On the other side of the coin – if you have 4 people living in a house, with say 2 adults and 2 teenagers – then yes , I would say this is definitely possible.

So how can you get around this problem of insufficient Amps , on your current electrical supply – there are two options in reality –

  1. Get a second 100 Amp supply to your property – contact UK Power Network, who are responsible for this on this link  – this option may well work out cheaper than having three phase supplied to your property.So basically you would have one electrical supply for all our household or flat requirements and a dedicated 240 volt , single phase supply for your central heating and domestic hot water via the electric combi boiler . The down side is that you will be paying an extra standing charge.
  2. The other option and possibly the best solution would be to get your electrical supply upgraded to Three Phase – Is it possible / How much is it to do this ? we don’t know , we just supply the boilers –again please contact UK Power Network , who are responsible for this, on the previous link mentioned.
  3. Or split your heating and domestic how water requirements into 2 separate units , either an electric boiler for the central heating needs and a indirect cylinder or calorifier for your domestic hot water requirements, or even a direct ( with electric immersion heaters ) cylinder / calorifier, more information on this system can be found on our web page here 

3 Phase – 400 Volt – Electric Combination Boilers

The only solution in reality to getting the higher performance outputs in both electric central heating requirements and domestic hot water performance is to use three phase as the electrical power supply.A three phase electrical supply isn’t fitted as standard to a normal house property in the UK, but can often be requested as the standard supply voltage especially when doing a new build, and can also be retrofitted to most existing properties.Many blocks of flats have a Three phase supply to them, as they use this to power the lifts etc, so if you require an electric combi boiler for a flat, then please check with your property management company , to see if this is possible to have a three phase supply to your flat.

As you can see from the data below , the range of power outputs is much larger when the electric combination boilers are powered by three phase, going all the way up to 48kW in output.

400 volt – Three Phase Electric Combi Boilers – Electrical Consumption – With Fuse and Cable requirements

ModelOutput in kWDraw Current – AmpsFused & Residual Current Device – AmpsCable Section
EDT10103* 15.23* 165* 2.5
EDT12123* 18.23* 205* 2.5
EDT16163* 24.33* 255* 2.5
EDT18183* 27.33* 325* 4
EDT20203* 30.43* 405* 4
EDT24243* 36.43* 505* 6
EDT30303* 45.53* 635* 10
EDT36363* 54.63* 635* 10
EDT40403* 60.73* 635* 16
EDT48483* 72.83* 805* 16


What size Electric Combi Boiler do I require ?

The first part of selecting the correct electric combination boiler is the central heating load or kW requirement. You can do this in a couple of different ways –

1. Consult a plumber or a heating services engineer –

A good qualified plumber will be able to do a heat loss calculation , but probably won’t have the design insurance indemnities ( which means that they have an insurance policy to claim off – if the system they design / recommend doesn’t work as stated.

If you want a “proper job” as they say you need to consult a CIBSE Heating consultant , who will do all the heat loss calculations etc –


But they will probably charge you £100 – £150 per hour of design – probably a minimum of £300 – but they do have insurance indemnities- therefore should the heating system not work / or not be adequate enough you have recompense.

2. The cost nothing , but your time method –

Or you could calculate the load yourself using the following website – which is a heat loss calculation app, this will tell you the heat load for each room, input the room data for your property , and them all up – and you end up with your total heating load


Quick note – the result will be in BTU’s – to convert to kW – divide the BTU’S by 3,412 to get the kW figure.

This heat loss calculator is very good an accurate if the information inputted is correct , I’m pretty sure that this ( or very similar) is what plumbers and heating consultants use on a daily basis to do heat loss calculations these days

3.Last but not least the ” Rule of Thumb ” , we don’t recommend using these at all , as they make a lot of assumptions and can be very dangerous ! but here we go – and use at your own risk

For underfloor wet heating systems – use 100 watts per m2 for concrete floors , and for suspended timber floors use 70 watts per m2

For a radiator heating systems – use an average of 1.5kW of output for every radiator. Thus if the central heating system has 10 rads – 10 x 1.5kW = 15kW of heating output is required

One kilowatt of heat will be required for heating every 10 square metres of your property. Thus, for heating a 50 square meters property, you would need a 5 kW electric boiler

We really wouldn’t recommend using these rules of thumb methods, use point 2 at the very least in our opinion, these heat loss calculators are very accurate these days, as long as the information entered is correct


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Electric Combi Boilers / Electric Combination Boilers from Flexiheat UK


Domestic Hot Water Performance of Electric Combination Boilers

The most important feature or aspect of electric combi boilers is the domestic hot water performance i.e. your bathing water , or hot water tap on the sink or wash basins. The amount of hot water an electric combi boiler can produce, is somewhat limited in the amount of hot water it can produce at any one time, especially when using single phase as the power supply, and serious consideration should be applied to splitting the domestic hot water demand , via a storage cylinder or calorifier ( either direct or indirect type ) should you have a larger property, or those with a higher level of domestic hot water usage.

Single Phase – 240 Volt  Combination Boilers – Domestic Hot Water Performance

ModelPower           (kW)Dimensions  H x W x D   (mm)Weight          (kg)Expansion Tank  Volume    (Ltrs)Δt  = 25°C Hot Water Amount  (Ltrs/min)
10EDM10700 x 400 x 2502675.8
12EDM12700 x 400 x 2502676.9
16EDM16700 x 400 x 2502679.2
18EDM18700 x 400 x 25026710.4


When used on a 3 phase supply, they start to get to a similar performance to a gas combi boiler in terms of hot water performance, as you can see from the chart below , producing 17.2 litres a minute , with a temperature rise of 25C.

Three Phase – 400 Volt Combination Boilers – Domestic Hot Water Heating Performance

ModelPower           (kW)Dimensions                  H x W x D   (mm)Weight          (kg)Expansion Tank  Volume    (Ltrs)Δt  = 25°C Hot Water Amount  (l/min)
10EDT10700 x 400 x 2502675.8
12EDT12700 x 400 x 2502676.9
16EDT16700 x 400 x 2502679.2
18EDT18700 x 400 x 25026710.4
20EDT20700 x 400 x 25026711.5
24EDT24700 x 400 x 25026713.8
30EDT30700 x 450 x 320341017.2
36EDT36700 x 450 x 320341217.2
40EDT40700 x 450 x 320341217.2
48EDT48700 x 450 x 320341217.2

With all of our electric combi boilers – domestic hot water always has priority, so should you have a domestic hot water (DHW) demand ,and the boiler is in the central heating mode at that time , it will temporarily shut down the central heating to satisfy the domestic hot water requirements.As soon as the DHW demand ceases,the electric combi boiler will automatically restart the central heating. This is called Domestic Hot Water priority.

Our Electric Combi boilers require a minimum pressure of 0.5 of a Bar to operate, and will work up to a pressure of 10 Bar on the cold water inlet for the domestic hot water. The temperature of this domestic hot water can be controlled between 35 to 55 degrees Centigrade.

Operating Parameters of our Electric Combi Boilers

 Technical           SpecificationsHeatingDomestic Hot Water
Minimum Operation PressureBar10.5
Maximum Operation PressureBar310
Minimum Setting Temperature°C3535
Maximum Setting Temperature°C8055

Download the Flexiheat UK Brochure for Electric Combi Boilers

Electric Combination Boilers For Flats 

Electric combi boilers can be the ideal solution to your heating and how water requirements when it comes to flats or bed sits. They are often very easy to install when compared to a gas or oil boiler as there are no flue requirements to thing about , which means you can basically place the boiler where are you want to.With there digital control panel these electric combi boiler for flats are easy to use and control, they are also aesthetically pleasing , and extremely quiet in operation. So if your require an electric combi boiler for your flat or bedsit, then give us a call, as we have the best range of electric combination boilers for sale in the UK.

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Electric Combi Boilers for Flats from Flexiheat UK

Frequently asked Electric Combi Boilers questions and answers –

  • Electric combi boiler installation – are easier than a gas or oil boiler for a few reason – the biggest being there is no flue pipe to install , thus the cost of this and the associated builders cost, such as making holes in brickwork or the roof for the flue are eliminated. This will often mean that fitting an electric combi boiler, is the cheapest of all combi boilers to fit when compared to oil or gas.
  •  Electric combi boiler cost – as a general rule they are slightly higher than their counter parts in gas at first impressions – but when you look at the extra’s such as the flue pipe etc, then they are around about the same price when you look at them as a package. When compared to oil combi boilers, then are cheaper on a like for like kW basis,even before you add the flue pipes and accessories.
  • Electric combi boiler prices – Electric combination boiler prices are at the mature stage of pricing cycle, they are a well established product and have been for many years.The most important thing to look for is not only the price, but also the associated quality. There are a few company importing far east manufactured products, that are using inferior components, and you also have to question the back up when it comes to spare and technical help.Our Electric combi boilers are manufactured in the EU , with quality components, that by law have to have spare parts available for at least ten years if a model or component gets updated, ask the one you found on ebay from the far east can guarantee this, then ask him to put it in writing. So in a nutshell, our electric combi boiler prices are competitive and more than fair, for the quality of product your purchasing,with the full technical back up we give and spares we carry – should you ever need any.
  • Electric combi boiler running costs or annual consumption costs  – These are easy to calculate. Get your current price you pay for a kilowatt hour or (kWh) of electricity and multiply it by the kW output of the boiler i.e. 17 Pence per kWh x 12 kW ( Output of your Electric Combi Boiler) = 17p x 12 = £2.04 per hour if your boiler is running constantly.  Electric combi boilers should be sized that on a minus 3 degrees C outside temperature , you can hold a constant temperature of 20 Degrees C internally within your home or flat.But in the real world , it very rarely works like this , as the day goes on , often the external temperature rises, your property benefits from solar gains from the sun etc. Here is a link to a energy consumption calculator , that may help you predict your running costs of your electric combination boiler.

Electric Combi Boilers – Electric Combination Boilers for sale UK & Ireland

Whether you want an electric combination or electric combi boiler for your property, be it a house,flat or bedsit ,or if you require one for a commercial and industrial application, then we have the best range here at Flexiheat UK to satisfy you demand with a range from 6kW to 48kW Output, and options of single or three phase. Should you require anymore assistance or information on our Electric Combination Boilers / Electric Combi Boilers for sale in the UK and Ireland, then please don’t hesitate to contact our sales team on 01202 822221 or click here for our email contact form