• Heating Advice

By: Bronte McClelland

Updated: 31st March 2025

Choosing the best combi boiler for your home can be an overwhelming task, leaving many wondering, ‘What is the best combi boiler to buy?’ The ultimate choice depends on your home and your budget - are you still confused? Don’t worry, we’ll provide you with some guidance so that you are able to make an informed decision.

In this comprehensive guide, we’ll cover essential factors for selecting a new boiler. Additionally, we’ll present a curated list of the best combi boilers highly praised by both homeowners and heating engineers.

If you already know which combi boiler you want, be sure to get boiler quotes from several heating engineers near you, to ensure that you get the best possible prices for the best boilers available. Comparing multiple quotes is critical to avoid overpaying for your new combi boiler. But how do you find qualified heating engineers at short notice?

Thankfully, Boiler Guide can help you with this. Get quotes from up to 3 local heating engineers by using our free, non-binding comparison service - it takes less than a minute to get started. Simply click the button below and find the best combi boiler to buy.

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How do you choose the best combi boiler to buy?

Going by the top brands, reading combi boiler reviews, and asking friends for recommendations are good ways to choose the best combi boiler. However, while this is all well and good, knowing if a particular combi boiler is best for YOU will come down to the size of your home and your household’s specific needs. Compare all of these factors to combi boiler prices to ensure you’re getting value for your money.

There are a few factors you need to take into consideration to spot the best combination boilers. First of all, let’s start with the factors that are always indicators of a good boiler regardless of your situation: efficiency and reliability.

Boiler efficiency refers to how well a boiler converts fuel into heat for your home. A good boiler wastes less fuel to generate the same amount of heat. This translates directly to lower energy bills and helps you save money over time.

Modern boilers are rated based on their ErP (Energy-related Products) efficiency rating, with A being the most efficient and G being the least. Opting for a high ErP-rated boiler can lead to significant cost savings in the long run.

Boiler reliability means the boiler performs consistently, delivering warmth dependably throughout winter with minimal breakdowns, ensuring peace of mind and a comfortable home.

Reliable boilers are built with high-quality components and designed for long-lasting performance. This way, you get fewer repairs and maintenance needs, saving you money and hassle in the long run. You can also get an idea of the boiler’s reliability by looking at its warranty - usually high-quality boilers come with a long-lasting one.

Our methodology for choosing the best boilers of 2025

The factors you need to consider that are personal to you and the type of property you have are:

• Budget: Buying a boiler is an investment, but you don’t need to compromise on quality to get a good deal.
• Size (output rating): Boiler sizing is measured in kilowatts (kW). A higher output doesn’t necessarily mean the boiler is better. What size you should buy depends on the number of bathrooms and radiators you have. If you don’t get the right size you might struggle to heat up your home or you could end up wasting money on high energy bills.
• Type of fuel: Boilers can be fuelled by gas, oil, LPG, biomass, or electricity. You need to check which types of fuel your boiler is compatible with. In the case of gas, you also need to check whether your home is connected to the gas grid.
• Dimensions & aesthetic: Many of us prefer to place our combi boilers out of sight in a cupboard. Even though combi boilers are known for being compact, it’s still a good idea to double-check the dimensions of the models you’re considering so they’ll fit into your home. You can also read combi boiler reviews to find the best small boilers. If your boiler isn’t located in a cupboard you might think twice about how it looks. As the name implies, Worcester Bosch’s Greenstar 8000 Style model is known to be one of the most aesthetically-pleasing boilers on the market.
• Noise level: The quietest combi boilers have a similar noise level to modest rainfall. If peace and quiet are a priority for you then it’s a good idea to look into combi boilers which are Quiet Mark-approved.
• Controls & accessories: Preferences on controls and accessories vary from person to person. However, a temperature control feature is standard for boilers, so all boilers on our list come with it.

Let’s dive into the top combi boilers we managed to find based on these criteria.

Boiler Guide's list of the best combi boilers on the market

1. Ideal Logic Max Combi Gas Boiler

• Price: £1,130 – £1,670
• Output range: 24.2kW
• Efficiency: 94%
• Warranty: 10 years

This model has the potential to lower your energy bills thanks to its efficiency rating of 94% and ErP A-rating for heat and hot water.

All combi boilers in the Logic Max range have a central heating output of 24.2kW which is suitable for homes with about 3 bedrooms and 10 radiators. The C35 model has a domestic hot water (DHW) output of 35.3kW, the highest in the range, which means it can meet higher demands for hot water.

Ideal has attached an extensive 10-year warranty to all of the Logic Max boilers to ensure you’re well covered after the installation.

2. Vaillant ecoTEC Plus Combi Gas Boiler

• Price: £1,500 – £2,100
• Output range: 20.4kW, 25.7kW, 30.1kW, 30.9kW, 32.2kW
• Efficiency: 94%
• Warranty: 10 years

The ecoTEC Plus is the ‘flagship’ Vaillant boiler model and is one of the best gas combi boilers. It is also one of the most efficient combi boilers on the market with a rating of 94%. It is available in outputs of 25, 32, 35 or the largest 38kW which is a great choice for larger homes with a high demand for hot water.

This boiler includes a 5-year warranty as standard with 7 or 10 years available when installed by a Vaillant accredited installer.

The ecoTEC Plus is also one of the more stylish models on the market with a backlit digital display, contoured case, and stainless-steel heat exchanger. The boiler has been awarded the Quiet Mark accreditation because of how quiet it is when it's operating.

3. Vokera Evolve C Combi Gas Boiler

• Price: £750 – £1,070
• Output range: 24kW, 28kW, 32kW, 36kW, 42kW
• Efficiency: 94%
• Warranty: 10 years

The Vokera Evolve C is another highly efficient gas combi boiler with a 94% efficiency rating. It has an ErP A-rating for heat and hot water. Furthermore, all of the models in this range are compatible with both natural gas and LPG.

This model is available in sizes 24, 28, 32, 36, and 42kW. Therefore, making it suitable for both small and medium-sized homes. In addition, all sizes come with a 10-year warranty so you can be sure that you are getting a reliable unit that is going to last.

4. Viessmann Vitodens 200-W B2KE Combi Gas Boiler

• Price: £1,900 – £2,000
• Output range: 25.4kW, 32kW
• Efficiency: 94%
• Warranty: up to 10 years

The last boiler on our list is the Vitodens 200-W combi gas boiler from Viessmann. It’s A-rated and has an impressive efficiency rating of 94%, which will help you waste less energy and less money.

This boiler is also compatible with LPG and its dimensions are 700 x 450 x 365mm (HxWxD).

It’s available in two sizes. One of which has a central heating output of 25.4kW and a hot water output of 30.5kW, making it suitable for homes with about 10 radiators and a single bathroom. The other one has a central heating output of 32kW and hot water output of 34kW, meaning it’s ideal for homes with around 15 radiators and up to 2 bathrooms.

This model has a standard warranty of just 3 years. However, it can be extended to 5 years when installed by a Viessmann-trained installer and even up to 10 years if you register it through the Viessmann online portal.

5. Grant VortexBlue Internal 36kW Combi Oil Boiler

• Price: £3,000 – £3,500
• Output range: 36kW
• Efficiency: 94.5%
• Warranty: 2 years

The Grant VortexBlue Internal 36kW Combi Oil Boiler has an impressive efficiency rating of 94.5% and a band rating of A. However, keep in mind the ErP (Energy-related Products) rating specifically for water is grade B.

The output rating of 36kW is best suited for larger homes with more than one bathroom. This combi oil boiler is also available in sizes 21kW and 26kW, although it’s important to note that the efficiency rating is slightly lower for these sizes.

Its warranty length is only 2 years. This is standard for combi oil boilers. However, it is possible to find brands that offer longer periods.

What is the most efficient combi boiler?

In 2025, the competition for being the most efficient combi boiler is definitely fierce. The efficiency of a boiler is dependent on both its efficiency rating and its band rating. We’ve selected our top 5 combi boilers based on how efficient they are:

1. Grant VortexBlue Internal 36kW Combi Oil Boiler

Grant VortexBlue key features:

• Award-winning Vortex condensing heat exchanger
• Market-leading Riello Blue Flame burner
• 24-litre expansion vessel
• High-quality external powder-coated casing
• Built-in frost protection

This high-efficiency boiler boasts an impressive 94.5% ErP rating, translating to less energy used and lower energy bills. An ErP rating refers to the amount of energy lost during heat and hot water production - the higher the rating, the better.

This A-rated boiler delivers on its efficiency promise. It not only helps reduce your carbon footprint but also translates to real savings on your heating costs.

Beyond efficiency, the VortexBlue Internal offers a maximum central heating output of 36kW, ideal for keeping your home warm even on chilly days. It also provides a domestic hot water flow rate of 20 litres per minute, ensuring a comfortable hot water experience.

2. Ideal Logic Max Combi Gas Boiler

Ideal Logic Max key features:

• A large digital display
• Boiler frost protection
• Reachable pressure gauge
• Hard-wearing and scratch-resistant case
• The Ideal System Filter – a magnetic and non-magnetic filter designed to protect domestic central heating systems from suspended black iron oxide.
• Compact dimensions and low lift weight, meaning potentially cheaper installation costs

The Ideal Logic Max boasts a user-friendly design that makes it easy to monitor and maintain. Plus, a readily accessible pressure gauge provides additional insights. Don’t worry about accidental bumps or spills - the boiler’s hard-wearing and scratch-resistant case ensures lasting durability.

Ideal Logic Max prioritises the health of your entire central heating system by incorporating The Ideal System Filter. This innovative filter utilises both magnetic and non-magnetic technology to capture harmful suspended black iron oxide particles. This filtration helps protect your system and potentially reduces the need for future repairs.

Some of the boilers in this range are also compatible with LPG heating (liquefied petroleum gas). This model has the potential to lower your energy bills thanks to its efficiency rating of 94% and ErP A-rating for heat and hot water.

All combi boilers in the Logic Max range have a central heating output of 24.2kW which is suitable for homes with about 3 bedrooms and 10 radiators. The C35 model has a domestic hot water (DHW) output of 35.3kW, the highest in the range, which means it can meet higher demands for hot water.

Ideal has attached an extensive 10 year warranty to all of the Logic Max boilers to ensure you’re well covered after the installation.

3. Vaillant ecoTEC Plus Combi Gas Boiler

Vaillant ecoTEC PLUS key features:

• Weather compensation
• Smart home integration
• Remote appliance care through myVAILLANT connect
• Flame lift detection system
• Instant hot water delivery in just 5 seconds
• Wide modulation range of up to 1:6 which ensure maximum efficiency

The Vaillant ecoTEC Plus prioritises both comfort and efficiency.  Enjoy hot water almost instantly - the boiler delivers it in just 5 seconds. When it comes to energy savings, the wide modulation range of up to 1:6 helps the boiler operate efficiently by adjusting its output precisely to your heating needs. Also, this boiler offers various output options, including models with a higher hot water output ideal for larger homes and longer showers.

The Vaillant ecoTEC Plus boasts a flame lift detection system that ensures quieter combustion. Plus, built-in two-stage frost protection offers an extra layer of security, giving you peace of mind during the coldest months.

The Vaillant ecoTEC Plus is compatible with the aroTHERM air to water heat pump hybrid system, allowing you to integrate a more sustainable heating solution in the future.

Finally, the Vaillant ecoTEC Plus offers a variety of control options to suit your needs. Choose from wired, wireless, or even smart controls with vSmart by Vaillant. This flexibility allows you to personalise your heating experience for maximum comfort and efficiency.

Are you interested in upgrading to a more efficient boiler for your home? Our team at Boiler Guide can quickly provide you with free, no-obligation quotes from up to 3 Gas Safe registered engineers. You can then easily compare their offers and select the best one without wasting hours of your free time endlessly researching.

Click the button below to get your free quotes now.

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What is the most reliable combi boiler?

As technology advances, so does the quality of boilers. New boilers have improved in many ways, including how reliable they are. It’s always good to look up reviews and ask people you know for their opinions and experiences with their boilers. However, considering how much boilers have improved in recent years, it’s a good idea to purchase a more recent model.

But how can you tell how reliable a boiler is if it’s new to the market? While customer reviews might still be unavailable, looking at a boiler’s warranty is a good indicator of how confident a brand is in the longevity of its boiler.

Below are our top 3 picks of the most reliable boilers available in the UK:

1. Worcester Bosch Greenstar 8000 Style Combi Gas Boiler

• Price: £1,630 – £1,800
• Output range: 30kW, 35kW
• Efficiency: 94%
• Warranty: Up to 12 years
• Key features: EasyControl system, solar compatible, maintaining the correct water level with Intelligent Filling system.

The Worcester Bosch Greenstar 8000 Style Combi Gas Boiler is known for both reliability and efficiency. This powerful boiler, with a central heating output of up to 35kW, is well-suited for larger homes.

It offers peace of mind with a 12-year guarantee when installed by a qualified professional.

Also, there’s an option for integration with solar heating systems, potentially boosting long-term savings.

2. Alpha E-TEC Plus Combi Gas Boiler

• Price: £850 – £1,100
• Output range: 26.1kW, 29.7kW, 32kW
• Efficiency: 93%
• Warranty: 10-13 years
• Key features: convenient maintenance with easy-access, dry-change NTCs, stainless steel heat exchanger, high-efficiency Grundfos pump and hydro block assembly.

The Alpha E-TEC Plus Combi Gas Boiler boasts a reliable feature - a stainless steel heat exchanger.

This material is commonly used in reliable boilers due to its corrosion resistance.

This boiler might be a champion of efficiency, helping you save on fuel costs and reduce your environmental impact. Its compact design could make it a great fit for various installation locations, even if space is at a premium.

Also, the Alpha E-TEC Plus might just be compatible with smart home systems for added convenience. It could be hydrogen-ready, meaning it might be adaptable to use hydrogen or blended gas mixtures, potentially future-proofing your heating system.

3. ATAG IC Economiser Plus Combi Gas Boiler

• Price: £2,100 – £2,700
• Output range: 23.2kW-31.2kW
• Efficiency: 94%
• Warranty: Up to 18 years (12 years standard)
• Key features: improved and efficient hot water production with the Economiser Plus patented technology.

ATAG IC Economiser Plus Combi Gas Boiler prioritises reliability with its unique iCon heat exchanger, backed by a lifetime replacement guarantee. This high-quality heat exchanger is likely resistant to corrosion, a major factor in boiler lifespan.

Additionally, the built-in passive flue gas heat recovery device and outside weather compensator work together to enhance the boiler’s performance and extend its longevity.

Which is the best value combi boiler?

ATAG IC Economiser Plus is our top choice for the best value combi boiler in the UK. As you can see in the table below, you don’t necessarily need to choose between having an efficient boiler or a reliable boiler - you can have both in one! The IC Economiser Plus comes out on top for being the most reliable, with a warranty of up to 18 years. It also scores high on efficiency with 94%.

Worcester Bosch Greenstar 8000 Style and Viessmann Vitodens 100-W B1KF are also great choices. They are A-rated with 94% efficiency and include warranties of up to 12 years, meaning you can save costs on your energy bills and be sure that you won’t need to think about replacing your boiler again for a long time. You can see a breakdown of these boilers and more in the table below.

We’ve also included an indication of the price in the table below. While there are a couple of affordable but still top-quality options, it’s important to note that a cheap combi boiler isn’t always the best value choice.

If a boiler is cheap but not efficient you’ll end up spending a lot on energy bills. And if a boiler is cheap but not reliable that means you’ll end up spending a fortune on frequent repairs and need to fork out for a replacement far too soon.

Leading combi boiler brands

All in all, with this guide, we tried to highlight the best combination boilers based on efficiency and reliability.

We measured our top combi boilers by a percentage and an ErP rating (A-G) since a higher percentage and better ErP rating indicate lower energy consumption.

We also factored in the warranty as it reflects the brand’s reputation and boiler’s reliability. So, the best boilers from our perspective are:

Top brands for efficiency (all 94%):

1. Grant VortexBlue Internal: Offers exceptional efficiency (94.5%) but a shorter warranty (2 years).
2. Ideal Logic Max: Economical with a 10-year warranty but lower hot water output compared to some competitors.
3. Vaillant ecoTEC Plus: Features a quiet operation and extended warranty (up to 10 years) when installed by a certified professional.
4. Vokera Evolve C: Versatile with LPG compatibility and a 10-year warranty across all sizes.
5. Viessmann Vitodens 200-W: Offers LPG compatibility and extended warranty options (up to 10 years).

Top brands for reliability (all with long warranties):

• Worcester Bosch Greenstar 8000 Style: Known for reliability with a 12-year warranty (when installed professionally) and potential for solar integration.
• Alpha E-TEC Plus: Features a corrosion-resistant stainless steel heat exchanger and a warranty of 10-13 years.
• ATAG IC Economiser Plus: Prioritises reliability with a lifetime heat exchanger guarantee and a lengthy warranty (up to 18 years).

Best value:

• ATAG IC Economiser Plus: Combines exceptional efficiency (94%) and a class-leading warranty, ranging from 12 to 18 years.

However, keep in mind that while these brands excel in specific areas like efficiency, reliability, budget, size, and features.

Conclusion: What is the best combi boiler to buy?

The choice of the best boiler depends on your specific needs and priorities. Therefore, there’s no single best combi boiler for everyone. At Boiler Guide, we have made our top 5 combi boilers:

• Most efficient boiler: Grant VortexBlue Internal 36kW Combi Oil Boiler
• Best warranty: ATAG IC35+ Economiser Plus 35 kW Combi Gas Boiler
• Most reliable boiler: Worcester Bosch Greenstar 8000 Style Combi Gas Boiler
• Best boiler for a large house: Vaillant ecoTEC Plus Combi Gas Boiler
• Most affordable boiler: Ideal Logic Max C24 Combi Gas Boiler

Factors to consider when choosing the best combi boiler

If you’re still on the fence, you can consider the following points to narrow down your search.

• Home’s needs and budget: Think about your hot water usage too. A large family with frequent showers will have different needs than a single person. Boilers range in price, so determine how much you’re comfortable spending.
• Fuel: Natural gas is often the most efficient and affordable choice, but depending on your location or existing infrastructure, oil or LPG might be necessary.  So consider any plans you have for your home.
• Efficiency: Look for a boiler with a high ErP rating (A being the most efficient). This translates to lower energy bills and helps the environment. The boiler’s output, measured in kW, should be sufficient to heat your home effectively. An oversized boiler wastes energy, while an undersized one might leave you feeling chilly.
• Features: Weather compensation automatically adjusts heating based on outside temperature, saving you money. Modulation allows the boiler to operate at varying outputs, further optimising efficiency. Smart controls put the power at your fingertips, making it easy to manage your heating system. A longer warranty provides peace of mind regarding potential repairs.
• Brand reputation: Research the brand’s reliability and customer service to ensure you’re investing in a quality product.
• Installer qualification: They can assess your specific needs, recommend suitable boiler models, and provide information on installation costs.

With careful planning and these helpful tips, you’ll be well on your way to finding the perfect boiler for your home, ensuring warmth and comfort for years to come.

Best combi boiler deals in 5 steps

Now that you know which combi boilers have the best value on the market, you need to figure out which ones are best suited for your home and budget.

Boiler installation costs can vary enormously depending on factors like how much work is required and even where you live. We’ve simplified the process so that you don’t get lost among all of the best combination boilers. Take a few quick steps:

Answer a few simple questions

To start you just need to answer a few straightforward questions using this boiler quotes form. These questions are simply relating to your home, the type of boiler you have and what you're looking for. You’ll also be asked for your postcode so that we can find heating engineers available near you.

Confirm your details

After you've submitted your enquiry, someone from our team will contact you to check we have the correct contact information and to make sure we understand exactly what you need. This means we can get the best boiler quotes for you, and you can sit back and relax.

Receive quotes and compare prices

You'll then be contacted by up to 3 Gas Safe registered heating engineers in your area. Sometimes the heating engineer can give you an estimate over the phone, however, usually, they’ll need to arrange a home visit so that they can see what they’ll be working with. This way they can assess the price more accurately, and then you can compare the quotes from each heating engineer.

Book your boiler installation

Now that you’ve received all the quotes, you can choose the one that works best for you. You can then arrange a convenient date and time for the work to be carried out by the heating engineer, and get the best combi boiler installed at the best price.

Get your best deal

Remember there is absolutely no fee for using Boiler Guide to find boiler quotes. And at no point are you under any obligation to accept any of the quotes you receive.

This way you can find out what the best deals for boilers in your area are without any extra expenses or pressure. If you’re curious about how much you could save on new boiler costs, simply click the button below to get started.

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FAQ

Which is the best combi boiler on the market?

Determining the absolute “best” combi boiler on the market is difficult because the ideal choice depends on your specific needs and priorities. ATAG IC Economiser PlusCombines exceptional efficiency (94%) and a class-leading warranty, while brands like Ideal, Vaillant, Viessmann, Worcester Bosch, Alpha and Grant also offer highly reliable boilers.

Which brand of combi boiler is best?

Worcester Bosch, Vaillant, and Viessmann are considered to be some of the best combi boiler brands. In particular, after reviewing multiple boilers, we can concluded that the Worcester Bosch Greenstar 8000 Style is the best combi boiler to buy in the UK for 2025. This is based on overall quality, value for money and output capacity of the combi boiler.

Which combi boilers to avoid?

You should avoid combi boilers with a low efficiency rating, as all new gas combi boilers in the UK are required to have a rating of at least 92%. The Ideal Logic Max, Worcester Bosch Greenstar 8000 Style, and Viessmann Vitodens 100-W are all efficient combi boilers you can trust with a 94% rating.

Which combi boilers last the longest?

High-quality boilers from well-established manufacturers should last for many years. Manufacturers also offer long warranties to show confidence in the longevity of their boilers. For example, the ATAG IC Economiser Plus Combi Gas Boiler has a warranty period of up to 14 years.

About the author

Bronte McClelland

Brontë is an experienced writer and editor for Boiler Guide. Her goal is to make technical topics more accessible and help UK homeowners find the perfect heating solution.

This article has been checked and approved by a Gas Safe registered engineer.