The most efficient gas boilers in 2025 are Viessmann Vitodens 200-W, Worcester Bosch Greenstar 4000, and Vaillant ecoTec plus.
The most efficient combi boilers in 2025 are the Viessmann Vitodens 200-W, Worcester Bosch Greenstar 8000+ Combi, and the Ideal Logic MAX Combi2
An A-rated efficient boiler can save you up to £490 per year.
Finding the best energy-efficient boiler is good news for your wallet, your home and the planet. Modern energy-efficient boilers waste less fuel than older models, helping you to save on central heating costs.
That’s because all gas boilers installed in the UK must use condensing technology. Condensing boilers recycle waste heat within the system, making them far more efficient.
We have carefully studied the current UK market to provide you with a definitive list of the most efficient boilers. In this article, we’ll help you find the perfect model for your home so you can get the best energy-efficient boiler.
One surefire way to find the most suitable option is to consult a heating engineer and get boiler quotes.
Yet, finding trustworthy installers can be a daunting task when done alone. You risk getting stuck in hours of never-ending googling. A busy homeowner like you doesn’t have time for that.
Fortunately, Boiler Guide can relieve this stress and help you find out how much a new boiler costs. By completing our 30-second form, you get up to 3 comparison quotes from local engineers.
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Boiler efficiency measures how well the boiler turns fuel into usable heat (for your radiators and hot water). Higher boiler energy efficiency means more heat is generated per unit of fuel consumed. This way, the overall fuel consumption numbers drop, and energy costs are reduced.
In the UK, energy-efficient boilers are graded through the ErP rating. It indicates the proportion of the boiler’s yearly heat production in relation to its total annual consumption of fossil fuel energy (e.g. gas or oil).
For example, an A-rating signifies that the boiler is at least 90% efficient. Therefore, only 10% of the fuel used is wasted (this means any heat generated during combustion which escapes via the flue pipe and is not considered 'useful' heat). In comparison, an old inefficient boiler may only be 70% efficient, rated 'G', meaning approximately 30% of its fuel consumption ends up as waste.
An A+++ energy classification indicates that an appliance is notably more efficient, surpassing a standard A-rated device by at least 30%. Each additional “+” symbol signifies a 10% increase in energy efficiency compared to the A rating. Consequently, an A+++ rating stands as the highest energy efficiency achievable for a boiler.
The specific energy efficiency rating of a boiler largely depends on the brand, model, and fuel used. Let’s take a closer look at these factors.
The most energy-efficient boilers in the UK
What is the most energy-efficient boiler in the UK? Well, it all depends on your heating needs, house size and preferences. Boilers come in different types, output sizes and fuel options – each with varying levels of efficiency.
However, when looking for the most efficient boiler, it’s important to make sure the boiler is suited to your home first.
Let's look at your options. Firstly, what type of boiler do you need? You have three options: combi, system and regular.
A combi boileris the best option for most UK homes with 1 – 2 bathrooms. It's compact and easy to install, making it the less expensive choice. It's also the best boiler for small flats as there's no need for large additional parts, such as water tanks or cylinders.
System boilerscome with a separate hot water cylinder and suit households with large hot water demands – perfect for those with 2+ bathrooms.
And last but not least, regular boilers(also referred to as conventional). They require a lot of space as they work in three parts: the actual boiler, a hot water storage cylinder, and a cold water feed tank. These are usually found in older homes and are only recommended in replacement scenarios (as they're very expensive to install new).
Depending on your boiler type, installation costs will vary. Factors like brand, system parts and local labour fees can add up. Fortunately, there are government boiler grants available that financial help to upgrade your home heating, if you are eligible.
However, the best way to find affordable boiler installation prices is to compare quotes from local heating engineers. Tracking down installers, though, can feel a bit overwhelming – eating up hours of your free time with calls and online searches.
Why not skip the hassle and fill in our simple 30-second form instead? We'll connect you with up to 3 local installers, who will provide free quotes with no obligations attached.
Gas is the most popular fuel option in the UK. This is because it's typically cheaper, cleaner and more direct to use (as it's pumped straight into most homes via the gas grid).
Gas boilers are also among the most energy-efficient options available, which is why we've chosen to prioritise gas models in our list.
To give you a quick overview of our most efficient boiler results, we've outlined the best performers for each boiler type (combi, system and regular) for you below.
Most efficient gas combi boiler: Viessmann Vitodens 200-W
Most efficient gas system boiler: Worcester Bosch Greenstar 4000
Most efficient gas regular boiler: Vaillant ecoTec plus
Viessmann Vitodens 200-W
Output range: 25kW, 32kW
Efficiency: 94 -98%
Warranty: 7-12 years
Price range: £1,835 – £2,090 (excl. installation)
Boiler type: Combi
The Vitodens 200-W combi boiler by Viessmann is one of the most efficient gas boilers. With a 94 – 98% efficiency potential, it's the best on the market today.
Moreover, this model is equipped with high-quality German-engineered systems that increase efficiency and performance while extending the boiler’s lifespan. These include the Lambda Pro Plus combustion controller, MatriX-Plus cylinder burner, and Inox-Radial heat exchanger.
Its output range of 25kW and 32kW also makes it the most efficient gas combi boiler for both small and medium-sized homes.
Worcester Bosch Greenstar 4000
Output range: 12kW-24kW
Efficiency: 94%
Warranty: 7 – 10 years
Price range: £1,150 – £1,400 (excl. installation)
Boiler type: System
The Greenstar 4000 range by Worcester Bosch is a top contender for the most efficient gas system boiler in the UK. Offering 94% efficiency levels, it's packed full of useful features.
For example, its Intelligent Filling System monitors the system pressure and automatically re-fills the system to the optimum level. Its large condensate siphon (500ml) increases the volume of condensate discharge, which reduces the risk of freezing.
These boilers have a wide power range to meet most heating and hot water requirements. Moreover, they are designed to operate well in low water pressure areas, ensuring optimal water flow.
Vaillant ecoTec plus
Output range: 12kW – 35kW
Efficiency: 94%
Warranty: 5-10 years
Price range: £1,200 – £1,750 (excl. installation)
Boiler type: Regular
For an energy-efficient regular boiler that's full of features and a great warranty offer, the ecoTEC plus from Vaillant boilers is great choice.
These boilers boast a high efficiency of 94% and come with 5 year standard warranty – extendable to 10 years when installed by a Vaillant Advance installer. They typically cost between £1,200 and £1,750 before installation fees (approx. £1,000 – £2,000).
Whilst we have marked these three models as our top picks, there are other valuable contenders you should consider. In the following sections, we'll look at each boiler type and help you decide which efficient boiler model is perfect for your needs.
Most efficient combi boilers in 2025
Combi boilers are compact heating systems that deliver hot water from one unit, meaning they don’t need to be fitted alongside a cylinder.
Combi boilers come in a range of highly efficient models, so you can save space and money on your energy bills. In this list, we've compiled the best combi boilers that offer high quality, performance, and efficiency.
To ensure you know how much a combi boiler costs, we've also included price estimates with each model. Here are our picks.
Ariston Alteas ONE+ Net
Efficiency: 94%
Warranty: 12 years
Output sizes: 35kW
Price: £1,050 – £2,550
Key features: Ultra-safe black glass front panel, compatible with 20% hydrogen (future-proofing) and remote control with the Artiston NET app.
This sleek-looking combi boiler is one of the most efficient and feature-filled options by Ariston boilers.
Apart from being 94% energy-efficient, the Alteas ONE+ Net has a generous standard warranty of 12 years, making it highly reliable.
This gas combi boiler boasts a stainless steel heat exchanger and ‘Auto Function’ that tracks and adjusts the temperature automatically, reducing energy consumption.
Worcester Bosch Greenstar 8000+
Efficiency: 94%
Warranty: 8-12 years
Output sizes: 32kW – 50kW
Price: £1,500 – £2,680
Key features: Optional unique Intelligent Filling System, wireless connectivity with the Bosch EasyControl smart thermostat.
Worcester Bosch Greenstar 8000+ boilers come equipped with advanced controls and wireless connectivity. The Greenstar 8000+ range boasts an impressive A-rated efficiency rating while also being an excellent hydrogen boiler solution.
Its large output range makes it powerful enough to support medium and large homes with multiple bathrooms. So it's a great option for those looking to save space.
The addition of a touch-screen display and wireless connectivity makes managing your heating easy. This reduces overuse and improves your whole central heating efficiency.
Ideal Logic MAX Combi2
Efficiency: 94%
Warranty: 7-10 years
Output sizes: 24 – 35kW
Price: £1,165 – £1,520
Key features: Compatible with smart thermostats, comes with an Ideal System Filter and is compatible with solar and hybrid systems.
The Ideal Logic Max range is the perfect choice for those looking for compatibility with smart thermostats or green technologies, such as solar thermal or low-carbon hybrid systems (which can increase your efficiencies even further).
Supplied with an Ideal System Filter, this boiler will be protected from internal system debris, increasing its lifespan. There is also a generous 10-year extended warranty available when you register the product within 30 days and service the boiler annually (other terms may apply).
Want to reduce your energy bills and increase home comfort? Now is a great time to replace your old, inefficient boiler with a new, advanced version. It'll not only save you money, but it'll perform better and, in most cases, you'll have more control than ever over your heating use with smart components and features.
To find the best price on a new efficient boiler, we recommend comparing quotes from several installers, but tracking down qualified engineers is a lot to manage on your own.
There can be endless research required, reading reviews and filling in forms. You may wait days or weeks to hear back! So why not avoid all this aggravation and fill in one 30-second form instead?
Using our service, you'll get connected with up to 3 qualified installers in your area. They can provide you with quotes and advice, so you can find the best deal.
It's completely free, with no obligations attached. Just click the button below to start.
System boilers can offer the same great efficiencies as combi models, but they can also provide larger quantities of hot water because they work alongside a hot water storage cylinder.
These boilers are ideal for homes with high water demands, such as those with 2 or more bathrooms or more than 10 radiators.
For our list, we've found the most efficient system boilers on the market today, with lots of additional features and perks. Let’s take a look.
ATAG iS
Efficiency: 94%
Warranty: 12 – 18 years
Output sizes: 15 – 40kW
Price: £1,000 – £1,500
Key features: In-built ErP pump to reduce energy consumption and increase efficiency, OneZone Temperature Control using the ATAG ONE Zone App.
This ATAG boiler comes with a wide range of output options, making it one of the most energy-efficient models suitable for both small and large properties.
The ATAG iS offers unique features to ensure a longer lifespan and ongoing efficiency. These include a stainless steel heat exchanger with a lifetime replacement guarantee and compatibility with solar thermal hot water systems.
What also makes this one of the best boilers available is its outstanding warranty offer, with 12 years as standard or 18 years when installed by an ATAG Selected Partner. It's perhaps the longest you'll find on the market!
Baxi 800 System 2
Efficiency: 94%
Warranty: 10 years
Output sizes: 18kW – 30kW
Price: £1,200 – £1,650
Key features: Adey Micro 2 Filter, compatible with Baxi uSense smart thermostat and app control
This Baxi boiler model comes with the Adey Micro 2 Filter, which guarantees optimal performance and durability by preventing unwanted particles from affecting your system’s efficiency.
With EasyFill, you can effortlessly maintain the central heating system pressure, eliminating the need for engineer visits. Baxi's pre-heated condensate trap is meticulously designed to thwart freezing during the colder months, safeguarding your system’s integrity and preventing frozen condensate pipes.
Whether you’re connected to natural gas or LPG, this boiler adapts to your needs without requiring a conversion kit.
Vitodens 100-W
Efficiency: 94%
Warranty: 10 – 12 years
Output sizes: 11kW – 32kW
Price: £1,415 – £1,65
Key features:Signature MatriX-Plus burner and Lambda Pro combustion controller inside, 20% Hydrogen ready, LED screen and mobile app control.
Another efficient boiler option from Viessmann is the Vitodens 100-W system model. It offers the same high-quality engineering that the company is recognised for, alongside some unique features.
This system boiler offers up to 94% efficiency, helped by its clean combustion systems and stainless steel parts that increase the overall lifespan.
Its connectivity also offers integrated WiFi controls through the ViCare platform.
If you’ve already got lost in the abundance of energy-efficient boilers out there, then you'll need professional advice. Yet, finding reliable and qualified heating engineers nearby can be a challenge. Thankfully, our team at Boiler Guide can help you.
We have a network of trusted Gas Safe registered engineers whose rates you can compare. Click the button below and we'll provide you with up to 3 free, no-obligation quotes from heating engineers in your area.
In the case of regular boilers, you’ll need cold water feed tanks in the loft and a hot water storage cylinder, together with the boiler itself. These boilers are now pretty dated and are mostly found in older properties. (Typically, if you require high hot water supplies today, you should opt for a system boiler).
However, if you're looking for a regular boiler replacement, there are many new models available. We've tracked down the most efficient regular boilers for our list, which are just as efficient as combi or system boilers. Let's take a closer look at our top picks.
Ideal Logic MAX Heat2
Efficiency: 93-94%
Warranty: 2-10 years
Output sizes: 12kW-30kW
Price: £1,215 – £1,575
Key features: Comes with an Ideal System Filter, compatible with the Halo thermostat range, and green technologies.
The Logic MAX Heat2 from Ideal Heating is a great upgrade choice for any homeowner with a regular boiler looking to improve their efficiency levels. This boiler has up to 94% efficiency (depending on the output size) and offers some additional energy-saving features.
For example, this boiler is compatible with low-carbon technologies such as solar thermal and hybrid heating systems, helping you reduce energy waste. It can also be controlled remotely through any Halo smart thermostat product.
With the added system filter and 10-year warranty offer (when registered within 30 days and serviced annually), this boiler is made to last.
If you're looking for cheap boilers in the UK, this model should be high on your list. The Ariston Clas ONE regular boiler has a small price tag of just £600 to £800, making it really affordable – whilst also offering high efficiency levels and a decent warranty length of 8 years.
It also includes features to enhance performance and prolong the boiler’s lifespan, such as its XtraTech stainless steel heat exchanger, smart thermostat connectivity and anti-frost device.
It also features an optimised internal silencer, guaranteeing quiet operation (50 dB) while maintaining peak performance.
Glow-Worm Easicom3 Regular
Efficiency: 94%
Warranty: 3 – 5 years
Output sizes: 25kW
Price: £620 – £900
Key features: LCD display for easy use, compact size for easy installation, manufactured in the UK (for greater availability)
The Glow-Worm Easicom3 regular boiler is a compact and affordable option that offers the same great efficiency levels as those in higher cost brackets.
While it only comes in one output size, a 25kW regular boiler is powerful enough to support high-demand households with 2+ bathrooms and up to 15 radiators.
This boiler also includes an aluminium heat exchanger for improved efficiency and a bright LCD display to make it easy to use. Added benefits include quiet operation levels and compatibility with Glow-Worm smart controls through its MiGo app system (to further reduce energy waste).
How much does an energy-efficient boiler save you?
Older boiler models are generally far less efficient than new condensing models. This is because boilers lose efficiency as they age.
New models also benefit from condensing technology, meaning they recover more heat that would have otherwise been lost through the flue during combustion.
If you install a new boiler, you’ll reduce the amount of energy needed to heat your home. Since new boilers are generally highly efficient, they will help you save on your energy bills.
For example, having a condensing A-rated boiler instead of a G-rated boiler can save you £490!
Savings with an energy-efficient boiler
Old boiler rating
Detached
Semi-detached
Bungalow
Mid-terrace house
Flat
D
(78-82%)
£220
£180
£160
£150
£65
E
(74-78%)
£270
£200
£180
£170
£75
F
(70-74%)
£340
£220
£210
£190
£85
G
(less than 70%)
£490
£320
£290
£270
£120
*Figures are based on expected savings when replacing an old boiler with a new A-rated condensing boiler. Including a programmer, room thermostat, and thermostatic radiator controls (TRVs) in a gas-heated home. Prices are based on Ofgem energy tariffs and data from the Energy Saving Trust.
If you want to reduce your bills and install a new, efficient boiler, you should compare quotes from local engineers. To help you cut out the pain of searching for hours, just fill in our simple 30-second form.
You'll get up to 3 free quotes with no obligations attached. Click the button below to get going!
What is the most efficient gas boiler in 2025?
There's no one exact most efficient gas boiler in 2025 in the UK. Some of the best energy-efficient boilers are produced by Worcester Bosch, Viessmann, and Vaillant.
What are the benefits of an energy-efficient boiler?
Energy-efficient boilers are an environmentally friendly option as they produce fewer emissions and contribute to a cleaner environment. In addition, they can use less fuel for heating which results in lower energy bills.
Are there energy-efficient boiler grants?
Yes, there are several government-backed incentives that provide funding for energy-efficient boilers. Contact a Gas Safe engineer to find out whether you qualify for a grant.
Which boiler is the most efficient?
There are several highly efficient gas boilers available in the UK, with different models and brands offering different levels of efficiency. Generally speaking, Ideal, Viessmann and Worcester Bosch offer the most efficient boilers in the UK.
How efficient is a 10-year-old boiler?
A 10-year-old boiler is usually 80-85% efficient. Upgrading to a new, energy-efficient boiler can lead to savings on energy bills of up to £490 and reduce your carbon emissions.
