5 Most Energy Efficient Boilers In 2025 – A Rated & Above

Most energy-efficient gas boilers – Which A-rated boilers are most economical?

With boilers accounting for up to 50% of monthly energy bills, upgrading to a high-efficiency model can make a bigger difference than you might think.

Modern A-rated boilers run at 90% efficiency or more, making them incredibly efficient.

This means that they turn over 90% of the energy they use into heat for your home, while older boilers might waste nearly half of what you’re paying for. 

So, if you want to save on your energy bills and reduce your carbon footprint at the same time, investing in a new, energy-efficient boiler is the smartest move.

In this guide, we’ll give you our recommendation for the most energy-efficient boilers available in the UK in 2025. Let’s get right into it.

Most Energy Efficient Combi Boilers

To curate this list, we’ve researched all the top boiler manufacturers and reviewed the best energy-efficient gas boilers.

1. Viessmann Vitodens 050-w Combi Boiler

Viessmann Vitodens Combi Boiler

The Viessmann Vitodens 050-w combi boiler is our first pick for energy efficiency. It’s one of the best combi boilers on the market, too, especially in terms of value for money.

Running at 92% energy efficiency, the Vitodens 050-w combi comes with a stainless steel heat exchanger, so it’s not only efficient but also built to last.

This boiler can modulate down to 1:8 of the power as and when required, so it only uses as little gas and energy as possible.

This is also one of the most reliable gas boilers on the market, so if your plan is to save money on your bills and spend as little as possible on a good hydrogen-ready boiler (20% blend), then this is the one for you.

Features 

• Compact and lightweight, so it can easily be installed in kitchen cupboards
• Quiet operation suitable for living spaces
• Features an intuitive LED touchscreen display for easy control and monitoring
• Available with output ratings of 3.2 to 35 kW for domestic hot water and 3.2 to 32 kW for heating
• Built-in WiFi allows for remote control via the ViCare smartphone app
• 7-year warranty, extendable by an additional 3 years

Price 

• Vitodens 050-W 25kW Combi Boiler – £1,035
• Vitodens 050-W 30kW Combi Boiler – £1,109
• Vitodens 050-W 35kW Combi Boiler – £1,265

2. Ideal Logic Combi 

Ideal Logic Combi

With its outstanding 94% efficiency level, Ideal Logic is one of the most gas-efficient boilers on the market.

This compact, wall-mounted combi boiler is available in three different outputs of 24kW, 30kW, and 35kW, making it an excellent choice for medium-sized homes.

Although the two-year warranty is relatively low, it can be extended to five or ten years. Alternatively, taking out a boiler cover plan is a great option because it’ll cover the cost of repairs and parts after your warranty expires. 

The Ideal Logic comes with boiler frost protection, which reduces the chance of your boiler freezing during the winter, and a digital display that makes it easy to monitor and adjust your heating settings.

Features

• User-friendly, backlit screen for easy control 
• Can be integrated with green heating technologies, like solar thermal and hybrid systems
• Adjusts power output to match heating demand
• Maintains minimal flow rate
• Built-in frost protection feature that prevents the boiler from freezing
• Compatible with various control systems, including the Halo range and OpenTherm controls

Price

• Ideal Logic Combi C24 – £750
• Ideal Logic Combi C30 – £845
• Ideal Logic Combi C35 – £950

3. Viessmann Vitodens 200-W

Viessmann Vitodens 200-W

With an impressive 98% efficiency rating, the Viessmann Vitodens 200-W is probably the most efficient gas boiler designed for larger homes.

The 200-W comes with a MatriX cylinder burner and a combustion controller, which work together to enhance energy efficiency and reduce maintenance costs.

Thanks to the integrated user-friendly WiFi interface, the boiler is easy to program to your exact needs. Should there be a problem, the installer is instantly informed via the app, ensuring that the boiler is always operating at top efficiency.

Features 

• Compact wall-mounted design suitable for various locations, including kitchen cupboards, utility rooms, and bathrooms
• User-friendly interface with a 7-inch colour touchscreen display
• Equipped with the MatriX-Plus burner with a stainless steel surface
• 1:17 modulation ratio for precise heating control and improved efficiency
• Includes built-in WiFi and can be remotely controlled via the ViCare app 
• Available in outputs from 2.5 to 32 kW
• Comes with a standard 7-year warranty, extendable to 10 or 12 years

Price

• Vitodens 200-W 30kW Combi Boiler – £1,940
• Vitodens 200-W 35kW Combi Boiler – £2,069

4. Worcester Bosch Greenstar Compact

Worcester Bosch Greenstar Compact

If you’re looking for a powerful combi, system, or regular boiler for your three-bedroom home with up to two bathrooms, the Worcester Bosch Greenstar Compact is an ideal option. With a 92% ErP efficiency rating, it’ll help keep your energy bills low.

We love all the different options for managing this boiler’s operation. Whether you prefer a mechanical option or the top tech option of an award-winning Hive thermostat, you’ll be able to balance your heating needs without wasting energy.

If you get it installed by a Worcester-accredited installer, the Greenstar CDi comes with a warranty of up to ten years.

Features 

• User-friendly interface with clear displays and simple control knobs
• Frost protection feature that prevents the boiler from freezing
• Smart controls adjust the heating based on the weather outside
• Compatible with both Natural Gas and LPG
• Available in outputs from 10 to 36 kW

Price

• Worcester Bosch Greenstar 28CDi Compact 24kW – £942
• Worcester Bosch Greenstar 32CDi Compact 32kW – £1,111
• Worcester Bosch Greenstar 36CDi Compact 36kW – £1,370

5. Vaillant ecoTEC exclusive with Green iQ 

Vaillant ecoTEC exclusive with Green iQ

With a hot water energy efficiency of 92% and a seasonal energy efficiency of 94%, the Vaillant ecoTEC exclusive with Green iQ is another solid choice if you’re looking for an efficient combi or system boiler. It’s the ultimate eco-friendly choice, given that 85% of its parts can be recycled.

The flow rate of 17.8 litres per minute means fast delivery of hot water, literally ‘on tap’. The ecoTEC is compatible with the vSMART™ control, meaning that you can control your boiler from a smartphone or tablet.

This is a boiler hand-made in Vaillant’s Derbyshire manufacturing plant, and it comes with a five-year warranty, which can be extended for another five years when fitted by a Vaillant installer.

Features 

• Green IQ mark—offers superior energy efficiency and reduced fuel consumption
• Self-adjusts to provide precise heating levels
• Quiet Mark approved, suitable for living spaces
• Designed for minimal fuel usage and reduced running expenses
• Works with advanced controls like sensoHOME

Price

• Vaillant ecoTEC exclusive with Green iQ 35kW – £1,518
• Vaillant ecoTEC exclusive with Green iQ 43kW – £1,768

How To Choose The Right Energy-Efficient Boiler For Your Home

Not sure which energy-efficient boiler is best for your home? Here are some key factors to consider.

Evaluate the size of your home and water usage

The size of your home directly impacts the type of boiler that will most efficiently meet your home’s heating and hot water demands.

You don’t want to waste money on a boiler that’s too big or end up with one that can’t keep up with your needs, so consider the number of bathrooms and bedrooms, as well as your hot water supply needs. 

If you have a smaller home with one or two bathrooms, a combi boiler will provide enough heat and hot water, while a large family home with multiple bathrooms will require a more robust system or conventional boiler. 

That said, some combi boilers can meet the hot water and heating demands of larger households, like the Vitodens 200-W, which is suitable for properties with over four bedrooms.

Check the boiler efficiency ratings

Energy efficiency in boilers is typically represented by letters A to G, with A being the most efficient, so look for boilers rated A (over 90%) for energy efficiency. All boilers on our list have over 92% energy efficiency, but the Vitodens 200-W tops the list at 98%. 

Consider the type of fuel

Boilers run on one of four types of fuel: natural gas, oil, LPG (Liquid Petroleum Gas), and electricity. Natural gas is the cheapest and most energy-efficient fuel. Gas-powered boilers also provide the fastest heating and hot water. 

However, if you live in a rural area with no access to the gas grid, oil and LPG boilers will bring you lower energy bills than electric ones. 

Look for features that save energy

Some modern models come with features that further optimise the boiler’s efficiency.

Modulating burners, like the MatriX cylinder burner found in the Vitodens 200-W, adjust the boiler’s output based on the home’s exact heating demands, which leads to significant energy savings. 

Weather compensation, found in the Greenstar 28CDi Compact, adjusts the heating based on the outdoor temperature. So, when it’s colder outside, the boiler heats the water more, and when it’s warmer, it heats it less, keeping your home at the right temperature without wasting energy.

Consider the price and warranty

While you might be inclined to go for a cheaper boiler that won’t break the bank, it isn’t always the most cost-effective option in the long run. A more expensive, highly efficient boiler requires a bigger initial investment, but it might save you more money in the long run.

The length of the warranty and what exactly it covers should also be taken into account. A 10-year warranty is becoming increasingly common and is considered a good standard to look for when purchasing a new boiler.

Summary 

As you can see, the UK boiler market doesn’t lack great energy-efficient boilers. Whether you’re looking for a compact unit for your smaller home, like the Viessmann Vitodens 050-w, or a more powerful option for a larger household, like the Vitodens 200-W, there’s an option to suit every home. 

Before you make a decision, remember to consider your home’s size and the boiler’s efficiency rating, fuel type, energy-saving features, and warranty. With the right boiler, you can keep your home cosy and warm while keeping your energy bills and carbon footprint in check.

To see our recommendations for the perfect energy-efficient boiler for your home, simply answer a few questions about your heating and hot water needs, and we’ll provide a fixed-price quote for your new boiler installation.

If you want to get a new boiler to reduce your energy bills but don’t have the funds right now to buy a boiler outright, then you can get one of our green boilers on a pay monthly basis.

If you choose one of our boilers on finance then you can spread the cost of a new cheap-to-run boiler and you could negate the amount you are spending every month.

FAQs

Which boiler is the cheapest to run?

Generally, the cheapest boiler to run is a new, energy-efficient, gas-powered combi boiler. 

However, it all depends on your home’s size, insulation quality, and hot water usage. Larger homes might find system or conventional boilers more efficient, while electric boilers might be cheaper to run in areas where electricity costs are low or if paired with solar panels.

How can an energy-efficient gas boiler save me money?

If your gas boiler was installed before 2005, it’s likely a non-condensing model with efficiency as low as 60%. This means you could be wasting up to 40% of the energy you’re paying for each month.

Modern condensing boilers, particularly A-rated models, are significantly more efficient. More efficiency means that you are getting more for your money when paying your central heating costs. 

According to the Energy Saving Trust, upgrading to an A-rated energy-efficient boiler could save you up to £490 per year on your gas bill.

The best combi boilers and the best system boilers available in the UK are designed to last much longer, so you won’t need to spend money on a new boiler and installation charges as often as you may have done before.

Can a boiler be 100% efficient?

Some electric boilers are labelled 100% efficient because they convert all energy into heat without producing any waste. The maximum efficiency of gas boilers is usually up to 94%. There are some exceptions, like the Vitodens 200-W, with its impressive 98% efficiency rating