Green Central avatar

Written by

Last updated:

Most Efficient Combi Boiler UK & Energy Efficient Boilers

Efficient Combi Boilers – Which has the highest efficiency?

viessmann vitodens 050-w combi boiler

Combi boilers are the most popular type of boiler in the UK and we would like to show you the 3 top/best rated and most efficient combination boilers which are available on the market.

Get fixed prices online in just 20 seconds – Click here

These are our top boilers in terms of, installation, efficiencies, operating costs, and maintenance/warranty periods and then the benefit is you can get a fixed price quote online now in under 20 seconds by clicking get a quote!

Hot Deals Icon

What Are Energy Saving Combi Boilers

Most Efficient Combi Boiler Uk

The energy-efficient combi boiler, also known as a combination boiler, is becoming increasingly popular, and over 70% of households choose to install it alongside a more efficient flue system.

However, if you are looking at more green systems and you are thinking of installing solar water heating, it should be noted that many combination boilers are not compatible with solar heating systems and cannot be used as effectively with these types of heating from solar equipment. 

Energy Efficiency Cost and Benefits at a Glance:

The cost of installing a new best combi boiler is between £1700 and upwards of £4000 depending on the system you are switching from and the type of installation you require. 

energy efficient boiler

This can be offset by the increased efficiencies as they are cheap enough to run while they keep you warm throughout the winter. Combi Boilers are fed their water from their main supply, which means they are much more efficient than other types of boiler, such as a gas boiler. 

This means that there is no need to install a separate storage for heating and a water supply tank, which makes them so much more efficient than other types of boilers. 

The best combi boilers are compact, require fewer pipes and do not require the additional installation of the water tank but would require the removal of said tank if you are switching from a regular boiler system.

Hot Deals Icon

Efficiencies of a Combi Boiler.

Intergas Rapid 25 Review

Combi boilers are indeed more cost-effective. They are so effective because they only heat the water they use, so they heat and cool more efficiently and are therefore more affordable. 

Combi boilers are a type of combined unit, which means they can heat your house and provide hot water without the need for a separate water tank or hot water storage cylinder. They tend to be more efficient when it comes to heating water on demand, as they combine two functions of your household into one compact system. 

This means that combined boilers can achieve incredibly high efficiency, which will not only help to reduce your carbon footprint, but could also reduce your energy costs. 

If you plan to replace your current boiler with a modern combi boiler, you can save energy costs over the course of a year. 

A combi boiler installed in a UK home can cover up to 90% of your household’s energy needs, with an average energy efficiency of 92%. 

A rated energy efficiency boilers

Every new boiler in the UK must be A rated or above this means that the boiler runs at 90% efficiency or more. Here is a quick guide on energy efficiency so you can see the difference between each rating. Most old boilers are not energy efficient and can be rated as low G, so switching to a new A rated boiler can save you £100’s of pounds every year.

Efficiency Ratings
A 90% or above
B 86%-90%
C 82%-86%
D 78%-82%
E 74%-78%
F 70%-74%
G 70% or below

In fact, the efficiency of a combi boiler is 92 percent lost in heat, meaning that only 8p of every pound spent on energy costs is wasted. Some systems such as the Viessmann Vitodens models can achieve a seasonal efficiency of up to 89%, an almost remarkable feat of engineering.

Top 3 Most Economical Boilers for 2023.

Compare Boiler Quote’s boiler and heating experts have compiled a list of the top 3 most efficient and cost-effective combi boilers in the UK. This is based not only on the efficiency rating but on the cost of boiler installation, maintenance and reliability or warranty period. All these boilers made our best combi boiler list too:

1.Viessmann Vitodens 100-W 30kW model

The top spot for the most energy efficient combi boiler of the year 2023, which produces the # 1 “best combination,” for most average-sized UK homes is the Viessmann Vitodens 100-W 30Kw. This is due to the price, the warranty, the efficiency, and the internal heat exchanger.

Vitodens 100-W 30kW Combi Gas Boiler Features:

viessmann vitodens 100-w
  • Band Rating: A Rated
  • ERP Rating: A HEAT A WATER
  • Efficiency Rating: 94%
  • Standard Warranty: 10 years
  • Output: 30kW
  • Flow Rate: 12 l/min
  • LPG Compatible: Yes
  • Mounting: Wall mounted
  • Typical Price: (inc VAT) £1,100
  • Typical installation Cost: £500 – £1,000
  • Typical Total Cost: £2,300 – £2,700
Hot Deals Icon

2. Ideal Logic Plus 24kW Combi Boiler.

With a 94% efficiency rating, and 9.9l/min flow rate, 7 year warranty included, the Ideal Logic plus is a highly efficient boiler with compact size and great reliability. The Ideal Logic Combi + C24 comes with a heating output of 24.2kW.  This allows the system to heat up to 10 radiators at once.

One of the main features of this particular boiler is its fully modulated operation for low outputs. What does this mean? Well, it means that it will only power and burn fuel for the amount of radiators you need heating, so if you only need half of your radiators heating, it will modulate for 5 radiators, saving you fuel and money!

Ideal Logic Plus 24kW Combi Gas Boiler Features:

ideal logic plus 24kw
  • Band Rating: A Rated
  • ERP Rating: A Heat A Water
  • Efficiency Rating: 94%
  • Standard Warranty: 7 years
  • Output: 24kW
  • Flow Rate: 9.9 l/min
  • LPG Compatible: Yes
  • Mounting: Wall Mounted
  • Typical Price: (inc VAT) £800
  • Typical installation Cost: (inc VAT)* £500 – £1,000
  • Total Average Installed Cost: £2,100 – £2,500
Hot Deals Icon

3. Worcester Bosch Greenstar 4000 30kW Combi.

The Greenstar 4000 30Kw is a very efficient and compact system with the capacity to provide hot water for up to 4 bed 2 bathroom homes, making it the perfect family home boiler system.

This particular system has the feature of an ErP (Energy Related Product directive) rating of A for both heat and hot water, thanks to its high heating efficiency of 94% and respectable flow rate of up to 12.3 litres a minute. 

Worcester Bosch Greenstar 4000 30kW Combi Gas Boiler Features:

  • Band Rating: A Rated
  • ERP Rating: A HEAT
  • Efficiency Rating: 94%
  • Standard Warranty: 7 Years
  • Output: 30 kW
  • Flow Rate: 10.8 l/m
  • LPG Compatible: Yes
  • Mounting: Wall Mounted
  • Typical Price: (inc VAT) £1,250
  • Typical installation Cost: (inc VAT) £600 – £1,000
  • Typical Total Cost: £2,250 – £2,650
Hot Deals Icon

Other Helpful Tips:

It is crucial to install the right performing boiler in your home, as combi boilers are available in a variety of sizes to meet a variety of heating energy needs.

These range from small to large heating capacities so it is important that you ask your heating engineer what size you need for your home. 

This is because a combi that is too small will not be able to meet your heating and hot water needs, while an over-powerful combi will ultimately drive up your energy costs. 

If you have plans to expand your home, add more residents, remodel attic space or add a conservatory, you will need a larger boiler to ensure it meets your long-term needs.

Unlike conventional boilers, which are also known as normal, traditional or conventional boilers, this boiler does not require any additional space for the tanks so again you could have more storage space with a combi system installed. 

There are many boilers that have warranties of 7 years or more, but normally you would want to see a boiler with an average warranty of at least 5 years when making your decision.

Are combi boilers more efficient than system boilers?

No is the short answer. You might also be wondering if switching to a combi from a system boiler will make any difference to the cost of running your central heating but this isn’t the case unless your hot water demands have really changed.

In this guide, we’re going to answer all your questions. We’re going to help you with all the information you need to know about how to ensure high levels of boiler efficiency while also making some recommendations for the most efficient boilers from a range of suppliers.

What is an energy efficient condensing boiler?

Condensing boilers use the generated heat more efficiently. That’s because when a fuel is burnt to produce hot water, gasses are released, and these are usually released through the flue.

That then means that in a non-condensing boiler, all the heat within those gasses is also lost resulting in higher heating bills to keep your home warm.

Where to get the best combi boiler for efficiency?

You can get a fixed price boiler quote online in under a minute using our quote calculator.

This is why we recommend Boiler Central as a supplier and fitter of boilers as they can offer you a new boiler quote with a huge 12 year warranty.

You could also consider the Viessmann Vitodens 050-w for a superb family system which will be reliable, efficient, easy to maintain, and a great family system for years to come. 

Thanks again for reading and we hope you enjoyed our information, please check back for more of the top tips on boilers in the U.K.

What about fuel type?

If you’re on the mains network, then a gas boiler is likely to be the cheapest option for you. Modern gas boilers, as the most popular form of heating, offer a wide range of choices for different sizes of home.

If gas combi boilers aren’t an option, then you may need to look at alternatives such as oil boilers and LPG but these are likely to be more expensive to run.

There is also a growing range of choices in sustainable fuels including wood and pellets. However, these can mean high prices initially for the purchase and installation and then in the cost of fuel to meet your heating demands.

Ways of improving boiler efficiency

Even a new boiler can do with a helping hand to enable them to reach top levels of efficiency. While heating engineers will be able to make some recommendations, here are some of our top tips. If you have an older boiler then getting a new boiler quote will show you just how much you can save!

Flue gas heat recovery

Even with the boiler using condensing technology, there is still going to be some heat loss through the flue system. A passive flue gas heat recovery system can recapture some of this lost energy within the hot gases and is then used to heat your hot water supply.

This recovery system is though only available for a combi boiler as the heat recaptured is used to heat the on-demand hot water system.

Thermostatic radiator valves

Which are the most energy efficient boilers? Compare Boiler Quotes

Thermostatic radiator valves allow you to control the temperature of a room by automatically adjusting the amount of hot water in the radiator. This then means that you have more control of the temperature for every room in the house rather than relying on a room thermostat

Most of us prefer a bedroom that’s a little cooler than the living room, with thermostatic radiator controls you can create different zones and temperatures throughout the home. That results in a highly efficient way of setting up a new boiler.

If you don’t already have these in place, the good news is that you’ll be able to fit them without calling in a heating engineer.

Programmer and room thermostat

Which are the most energy efficient boilers? Compare Boiler Quotes

It should come as no surprise that the more control you have over your central heating, the easier it becomes to improve boiler efficiency. The most efficient heating system is often one that’s controlled through a smart thermostat.

These systems allow you to manage the heating controls via your smartphone or tablet. Then, no matter where you are, you can switch the heating on or off. The smartest systems also detect when windows have been left open when the heating is on and when there’s no one at home.

As a result, smart technology and its heating controls can greatly enhance energy efficiency.

Making sure you get the right size of boiler helps efficiency

So, you’ve narrowed down which type of boiler you need, next you need to consider what size of boiler is needed. Boiler size is assessed by its heat output and that’s then measured in kilowatts.

Which are the most energy efficient boilers? Compare Boiler Quotes

It used to be recommended that homeowners should go for a larger boiler than they really needed. That was to allow for the heat that was lost through the boiler’s low levels of energy efficiency. However, the larger the boiler is the more energy that’ll be used to heat your home.

Now, the most energy-efficient boiler types lose very small amounts of heat there’s no longer any need to upscale the boiler size. That then means that getting an efficient boiler is only one half of the equation, it also needs to be the right size, and then you’ll get the energy saving.

If you’re not sure what size of boiler you need, then get a free quote for your new boiler

Hot Deals Icon
Green Central avatar

Written by

Read some of our superb solar panel installation reviews from Trustpilot

Recently had solar panels fitted by Green Central and I can’t speak highly enough of the team. The whole experience has been trouble free and I would recommend them to anyone thinking about having solar panels installed – 10/10!

Rob Schofield


Our installation is now complete! 8 solar panels fitted and the journey from initial consultation through to the end product has been seamless.
Hats off Green central, Credit where it’s due.
Will definitely spread the word!



Recently had six solar panels fitted on my house by Green Central and I couldn’t have asked for a better service. In particular, I have to highlight the exceptional communications through out, the over all smooth running process and completely stress free experience, all down to Green Central. I now have grid independence which is valuable beyond estimation.


Name *
Email *
Phone No. *
Post Code *
Name *
Email *
Phone No. *
Post Code *