For many homeowners, the heart of a warm and efficient home lies in the choice of boiler and combi boilers are a popular choice for many. Renowned for their efficient operations, A-rated boiler models have become synonymous with reduced energy bills and sustainable living. 

A new combi boiler could:

  • Save up to £840 annually on your energy bills
  • Provide unlimited hot water on demand
  • Reduce emissions compared to regular and system boilers

In this article, we’ll explore the intricacies of combi boilers, shedding light on their features and benefits. Whether you’re in the market for an upgrade or simply curious about how they function, understanding the impact and advantages of combi boilers is essential for every homeowner aiming for optimal home heating.

Find out about 0% VAT measures on energy efficiency installation.

Combi boilers are an efficient way to heat your home

Combi boilers are an energy efficient, money saving way to heat your home. (Image credit: Adobe)

What are the best combi boilers?

How much do combi boilers cost?

Installing new A-rated combi boilers comes with a varied cost range. The cost of installing new combi boilers depends on the size of the boiler, brand and installation price. However, based on our research and using the costs from our reviewed brands, the below table is the average cost of a combi boiler in the UK. 

Boiler typeAverage combi boiler costAverage combi boiler installation priceAverage cost of combi boiler including installation
Combi boiler£1,200£400 – £2,000£1,600 – £3,200

What affects the cost of installing a new combi boiler?

As well as the average cost of installing a combi boiler which can cost between £1,500 and £2,200, you should also consider the additional parts. According to Energy Saving Trust, adding other parts could cost up to £4,000. 

Additional parts may include:

  • Thermostatic heat controls
  • Magnetic filter
  • System power flush
  • New boiler flue pipe
What type of property is the new boiler for?
It takes just 60 seconds

How much can you save with a new combi boiler?

Installing a new combi boiler can save you a great deal of money on your energy bills, and what with the ongoing cost-of-living crisis, this is beneficial to most. But, how much you can save will depend on your house size and energy rating. 

According to Energy Saving Trust, this is how much you can save if you replace your old gas boiler with a new A-rated combi boiler based on October’s energy prices.

Old boiler energy efficiency rating
Property typeD (78-82%)E (74-78%)F (70-74%)G (<70%)
Mid-terrace house£235£260£290£420
Semi-detached house£305£335£380£540
Detached house£375£460£590£840

Is a combi boiler gas or electric?

Combi boilers can be powered by gas or electric. But, gas powered combi boilers are more readily available and therefore tend to be cheaper because of this.

Below is a comparison of electric boilers vs gas boilers.

Electric combi boilerGas combi boiler
More expensive to run (high energy electricity prices)Cheaper to run
Electric combi boilers have an ErP rating of DHeat hot water directly from the mains when you turn on the tap – this makes it more economical
Doesn’t burn fossil fuelsBurns gas (fossil fuels)
Less common in the UKMost common combi boiler in the UK

Combi boiler reviews

Worcester Bosch Greenstar 38CDi Combi

The Worcester Bosch Combi Greenstar 4000 boiler is compact and can be wall-mounted to save space in the home.

The Worcester Bosch Combi Greenstar 4000 boiler is compact and can be wall-mounted to save space in the home. (Image credit: Worcester Bosch)

  • Guarantee options: Up to 10-years guarantee 
  • Price: £1,559.99
  • Efficiency rating: A
  • Output rating: 30kW

Worcester Bosch (sometimes simply called Worcester) is a UK-based heating and hot water product manufacturing company founded in Worcester in 1962. For the best all-around combi boiler, we’ve chosen the Worcester Bosch Greenstar 38CDi. Compared to other combi boilers it has some of the best features that would benefit most households. 

One of the main reasons that we’ve chosen the Worcester Bosh Greenstar 38CDi is its higher-than-average output rating. With a maximum output rating of 30kW, this combi boiler is suitable for a range of household sizes. The Greenstar combi boiler can comfortably heat homes with up to 15 radiators, so would be beneficial for homes with up to four bedrooms. 

For smaller homes, the Greenstar 38CDi’s water flow rate will be more than enough to supply hot water to taps and their one bathroom. When it comes to larger homes, and particularly those with more than one bathroom, we would also recommend the Greenstar 38CDi as a good option. In fact, its water flow rate of 16.4l per minute is well above average and it’s not often that combi boilers have a large output rating and also benefit from a high flow rate. 

There’s one sticking point that could let this combi boiler down in terms of added luxuries. 

The Greenstar 38CDi doesn’t come with smart controls. It comes with pretty standard controls like holiday mode, pre-heat mode to get hot water faster and an eco mode for energy saving, but you won’t be able to use your smartphone to control your heating when you’re away from home.      

Worcester Bosch receives a 4.6-star rating on Trustpilot, which is quite impressive compared to other boiler manufacturers. 


The Worcester Bosch Greenstar 38CDi is a fair price compared to other models, and it does come with excellent features. 

Worcester Bosch Greenstar 38CDi
Average cost excluding installation£1,559.99
Average installation cost£400 – £2,000
Total cost£1,959.99 – £3,559.99

Baxi Duo-Tec 33 Boiler

Cut heating bill boiler installation

New combi boilers are more energy efficient than older models. (Image credit: FMB)

  • Guarantee options: 7-year guarantee on parts and labour 
  • Price: £1,079
  • Efficiency rating: A
  • Output rating: 28kW

Installing a new A-rated combi boiler can be a costly investment. If you’re on a budget and are looking for an affordable combi boiler that still comes with great features, we recommend the 

Baxi Duo-Tec 33 Gas Combi Boiler. It’s below the average price of a combi boiler and comes with A-rated energy efficiency. 

To find the most affordable boiler that still has a lot to offer, we looked for a combi boiler that would suit a variety of home sizes. Manufactured in the UK, the Baxi Duo-Tec has a maximum central heating rating of 28kW. Both small and medium-sized homes with up to 15 radiators could benefit from this combi boiler.  

The Baxi Duo-Tec 33’s water flow rate was another reason we chose it as a more affordable combi boiler. With a water flow rate of 13.5l per minute, it’s capable of meeting the average household’s hot water demands. It should also be able to have your shower running at the same time as the taps. 

It’s also suitable for small homes that might be concerned with space. At (h)780mm x (w)450mm x (d)345mm, it is compact enough to be stored inside a bathroom cabinet or kitchen cupboard, ensuring you don’t lose any household space. 

Receiving a 4.4-star Trustpilot rating is another reason we’ve recommended the Baxi Duo-Tec 33, as customer reviews shine a light on Baxi’s quick installation and reliable products. 

As the UK moves towards greener energy, homeowners will need to consider this when installing a new combi boiler. The Baxi Duo-Tec comes hydrogen-ready, which means should new UK legislation come into effect you needn’t worry about installing a new combi boiler. 


The Baxi-Duo Tec 33 combi boiler is priced very affordably compared to others on the market and has a lot to offer in terms of output rating and water flow rate. 

Baxi Duo-Tec 33 Gas Combi Boiler
Average cost excluding installation£1,079
Average installation cost£400 – £2,000
Total cost£1,479 – £3,079

Viessmann Vitodens 050-W Combi

Viessmann Vitodens 050-W combi boiler kitchen

The compact Viessman Vitodens 050-W combi boiler can fit into a small kitchen seamlessly. (Credit: Viessmann)

  • Guarantee options: 7-year guarantee on parts and labour 
  • Price: £1,039
  • Efficiency rating: A
  • Output rating: 30kW

For small homes, it’s unnecessary to pay for more than what your home needs and will use. Small homes typically have one bathroom, so the maximum output rating required is much lower than what’s needed for larger homes. 

We recommend the Viessmann Vitodens 050-W, as it’s powerful enough to heat small homes and supply enough hot water and it’s also a low-cost option compared to other combi boilers with similar features.

The Viessmann Vitoden 050-W has a maximum heating output of 25kW. Small homes with up to 10 radiators need between 24kW and 27kW of heating output, so the Viessmann combi boiler is a good choice for homes with only one bathroom. 

The maximum hot water output is slightly higher at 30kW, and the water flow rate is 14 l per minute. Small homes, especially with one bathroom, usually require between six and 12l of water per minute, which is why the Viessmann Vitodens 050-W is a front-runner here. It’s quite rare to find a combi boiler that has a high water flow rate for a below-average price. 

The Viessmann Vitodens 050-W is WiFi integrated and you can use the Viessmann app to control your combi boiler’s temperature. Using its smart controls, you can programme your combi boiler to heat your home at times that suit your schedule. This handy tool gives you full control and can even help you save money on your energy bills. 


Viessmann Vitodens 050-W 30kW Gas Combi Boiler
Average cost excluding installation£1,039
Average installation cost£400 – £2,000
Total cost£1,439 – £3,039

Ideal Vogue GEN2 Combi C40

The Ideal Vogue Combi boiler has a slim, compact design to fit neatly into your home.

The Ideal Vogue Combi boiler has a slim, compact design to fit neatly into your home. (Image credit: Ideal Heating)

  • Guarantee options: 10-year guarantee 
  • Price:£1,259
  • Efficiency rating: A
  • Output rating: 32kW

You can determine if your home falls into the larger homes category by identifying how many radiators you have. Typically, a larger home has over 10 radiators and more than likely has two or more bathrooms. 

If you have a larger home, we recommend the Ideal Heating Vogue GEN2 Combi C40 Gas. This combi boiler has the capacity to heat a larger home and supply enough hot water for more than one bathroom.

Ideal Heating’s GEN2 C40 combi boiler has a maximum heating output of 32kW, so it is well suited to homes with 10 to 15 radiators. Throughout our research, we found that this combi boiler came out on top in comparison to other models with a similar output when other factors like price and water flow rate were also taken into account.

Larger homes usually have more than one shower, or they may have a shower and a bath. To run a bath in a desirable timescale, as well as having a hot water supply to a shower and taps simultaneously, your combi boiler would need a considerable water flow rate. The Vogue GEN2 C40 has a water flow rate of 16.4l per minute, which is sufficient enough to cope with larger homes’ water supply demands. 

A downside to this combi boiler is that it is not smart control integrated, which means you won’t be able to use your smartphone to control the boiler. However, it comes with a standard level of heating control and you’re still able to programme your central heating to turn on at desired times. If this isn’t a priority for you, then the Vogue GEN2 C40 really is one of the best combi boilers on the market for larger homes.


Ideal Heating Vogue GEN2 Combi C40
Average cost excluding installation£1,259
Average installation cost£400 – £2,000
Total cost£1,659 – £3,259

Vaillant ecoTEC 835 Exclusive with Green iQ

Vaillant ecoTEC exclusive combi boiler kitchen

The Vaillant EcoTEC exclusive combi boiler range is compact and Quiet Mark approved, so it’s ideal for kitchen installations. (Image credit: Vaillant)

  • Guarantee options: Up to 10 years 
  • Price: £1,788.98
  • Efficiency rating: A
  • Output rating: 35kW

There could be a number of reasons why you’d be looking for a powerful combi boiler. The most obvious is to power a large home with over 15 radiators or to supply hot water for multiple bathrooms. Our choice for the most powerful combi boiler is Vaillant ecoTEC 835 exclusive with green iQ.

Valiant is a trustworthy brand and is the second largest boiler manufacturer in Europe and is best known for its environmentally friendly products. The ecoTEC 825 is hand-built at the company’s Derbyshire manufacturing plant.

The ecoTEC 835 benefits from Vaillant’s unique green iQ technology. The Green iQ mode optimises running cycles which results in lower gas consumption and the combi boiler is highly recyclable at the end of its lifespan. This makes it one of the most energy-efficient combi boilers on the market and a good choice for homeowners who prioritise keeping energy bills low. 

To find the most powerful combi boiler, we considered output rating and water flow rate. The ecoTEC 835 surpasses others on the market on both of these metrics. With a maximum heating output of 35kW, this combi boiler is suitable for small, medium and large-sized homes with up to 20 radiators. 

We found that a lot of combi boilers with a similar heating output fell short when it came to the water flow rate. It’s important not to forget this factor, as it dictates how many water faucets can be used at one time. The Valliant ecoTEC has a water flow rate of 14.5l per minute, and this is enough to supply hot water to more than one bathroom within your home.  

As a brand, Vaillant is eco-conscious and its products reflect this. As well as featuring high energy efficiency and low emissions, it comes with integrated vSMART controls. This smart feature helps to keep energy bills low since the technology can adapt itself to adjust your central heating to the exact amount that your home needs. The smart control also allows you to control your heating when you’re not at home, so you never need to worry about waiting for your house to warm up after you get home ever again. 

Speaking of eco-conscious, Vaillant prides itself in working towards low-carbon solutions. All of its boilers have been tested with a 20% hydrogen with natural gas blend as part of the HyDeploy Project

The ecoTEC 835 comes with up to 10 years’ guarantee when it’s installed by a Vaillant Advance Installer, which is a fairly standard length offered by leading boiler manufacturers. If you’re looking for a trustworthy, powerful combi boiler, Vaillant – with its 4.5-star Trustpilot rating – is a good choice with positive customer reviews. 


The ecoTEC 835 is priced well above the average combi boiler cost. This is not surprising when you consider the above-average features like high heating output and smart controls. 

Vaillant ecoTEC 835 exclusive with green iQ
Average cost excluding installation£1,778.98
Average installation cost£400 – £2,000
Total cost£2,178.98 – £3,778.98

Are there any grants to help with combi boiler cost?

Installing a new combi boiler can be a costly investment. Although this investment could save you up to £840 per year on your energy bills, the initial cost might put some homeowners off.

The government has set up the Boiler Upgrade Scheme in its bid to make the UK more energy efficient by 2050. Unfortunately, the BUS is only available for biomass boiler installations. However, the Energy Company Obligation (ECO4) is designed to help vulnerable households. 

The Energy Company Obligation 

The Energy Company Obligation (ECO) scheme is designed to help vulnerable UK households afford energy efficient upgrades, including new heating systems. You may be eligible if you receive one of these benefits: 

  • Child Tax Credit
  • Working Tax Credit
  • Universal Credit
  • Pension Guarantee Credit
  • Pension Savings Credit
  • Income Support
  • Income-based Jobseeker’s Allowance (JSA)
  • Income-related Employment and Support Allowance (ESA)
  • Child Benefit
  • Housing Benefit

Contact your local council to apply, or contact your energy supplier directly.

How to find the best combi boilers 

Choosing the best combi boiler can be confusing. The most important factor to consider will be the size of your home and your consumption needs. Large or older homes may require a system boiler (or regular boiler), but most homes can get away with installing a much more compact and affordable combi boiler. These are the factors that need to be taken into consideration:

1. Heating output

Combi boilers are rated by their kilowatt (kW) rating or heating output. As a general rule of thumb, you need at least 2kW per radiator; e.g. a house with 10 radiators will be able to use a 24kW combi boiler. 

However, the lower the heating out, the fewer litres that can be heated per minute. If you have several bathrooms and several people living on the property, you may want to buy a combi boiler with a higher output to avoid issues down the line. 

A four-bedroom house with more than three bathrooms and up to 20 radiators, for example, shouldn’t settle for a combi boiler with a wattage lower than 35 or even higher. If you live in a multi-storey home, you may want to consider a more powerful boiler – the longer the pipework between the tap and the boiler, the longer you’ll have to wait for hot water. 

2. The number of occupants

The number of bedrooms and occupants can have an impact on the performance of your boiler. The larger the home, the greater the demand placed on your central heating system. 

If several occupants share multiple bathrooms, you will need a bigger boiler as the likelihood of simultaneous hot water demands (e.g. bathing) is much higher. If you have more than one bath or shower in the home, using them simultaneously will be tough with a smaller combi boiler. 

3. Type of fuel

Most households in the UK use mains or natural gas, but a few isolated buildings aren’t connected to the gas network and use LPG bottles or oil. This may influence the type of gas boiler you can use. LPG has lower carbon emissions and is the most efficient fuel type. 

4. Energy efficiency 

Environmentally-conscious consumers must consider the energy efficiency of their boiler as it can account for more than half of the emissions generated by the home. If your boiler isn’t efficient, it wastes energy and drives up the heating costs of your home. An A-rated, high-efficiency boiler can have hundreds of pounds a year, especially if you opt for a boiler with a good heating control system (which allows you to choose which rooms are heated and when). This can prevent you from wasting energy heating unused rooms. 

5. Cost

Combi boilers are far more affordable than regular boilers, but they aren’t cheap. The cost of the boiler can be as low as £575 but always take installation cost (and the cost of venting, accessories and components) into account. These costs are often as high (or higher) than the cost of the boiler itself. 

6. Warranty

Most boilers are built to last at least 10-15 years. A faulty boiler is expensive to repair or replace, and any disruption to your central heating and hot water supply is unpleasant to deal with, especially in winter. Look for lengthy and comprehensive warranties when you make a purchasing decision. That way, if anything goes wrong due to a faulty boiler or shoddy workmanship, you have some recourse to resolve the issue quickly and affordably. 

7. Experience 

The longer a company has been in business, the better. Several years (or even better, decades) of experience shows that the company has the longevity and experience to install and manufacture a quality boiler that will give you years of use. Most of the companies we reviewed have at least 20 years of experience or more backing their business. 

Why should you install a combi boiler?

Gas boiler and electric water heater. Home furnace, tank isolated on blue background. System of combi heating. White smart gas boiler with burner for heat water with hot, cold pipe and control. Vector

Combi boilers are compact and ideal for space saving. Image credit: Adobe

1. Combi boilers are more compact

Compared to conventional boilers, combination boilers are very small. There’s no need to store hot water (although hybrid models exist), which saves space and decreases the risk of your pipes freezing during winter. The average combi boiler can fit easily into an airing cupboard or kitchen, freeing up your roof space. Their size makes them much easier to install and maintain, as well.

2. Cost savings

Combi boilers are highly efficient. Most of the combi boilers listed in this article are more than 90% A+ efficient, making it extremely affordable to heat your home. Traditional boilers heat vast quantities of water, which means that they expend a huge amount of energy, whether you are taking a shower or simply washing your hands. Combi boilers have to heat much smaller quantities of water. Most modern combi boilers are also fitted with smart temperature controls that allow you to choose which rooms to heat and when. 

3. Fast access to hot water

Combi-boilers heat water according to demand – there’s no need to wait for the water to be heated. The experience of using a combi boiler (and queuing to use the bathroom) is much more pleasant because there’s no risk of running out of hot water. Some of the more powerful combi boilers on the market can heat homes with several bathrooms and occupants, solving hot water issues for good. 


Choosing a combi boiler for your home shouldn’t be a guessing game. We’ve spent hundreds of hours gathering research to determine the best combi boilers on the market according to consumer needs.

Market leader Worcester Bosch has a number of excellent, reliable combination boilers to choose from, at fair prices, with long guarantees. The company has a stellar reputation, good customer ratings, and a wide range of products to choose from. We recommend the Worcester Bosch Greenstar 38DCi as the best all-around combi boiler, it has a good balance of heating output, water flow rate and is still a compact size for smaller homes.

If affordability is the primary driver, the Baxi Duo-Tec 33 combi boiler offers great quality, a solid 7-year warranty and a low price for the cost-conscious consumer. This boiler is also energy efficient enough to cut down your power bills considerably, extending your cost savings for years to come. 

For homeowners with small homes, we highly recommend the Viessmann Vitodens 050-W 30kW. This combi boiler is compact and will fit inside the standard kitchen cupboard. It’s heating output an water flow rate will meet the demands for a small household too.

For those with larger homes, multiple occupants and several bathrooms that will be used simultaneously, the Ideal Heating Vogue GEN2 combi C40 is a better option. You’ll find that the Vogue GEN2 has a high energy efficiency, which should be high on the priority list for larger homes. We also commend Ideal Heating’s 10-year warranty, it is one of the longest we’ve come across in our research.  

If you’re looking for a powerful boiler but are also concerned with your carbon footprint and energy efficiencies, you should consider the Vaillant ecoTec exclusive Green iQ Combi Boiler. Vaillant has focused on environmental friendliness in both design, features and the materials used. Homeowners who choose this brand can rest assured that their boiler will be durable, silent, economical and nearly full recyclable at the end of its lifecycle. 

While every single one of these leading brands offers quality and value for money, it’s important to consult with an expert installer before making a final decision. Even the best-reviewed combi boiler may fall short if the wrong wattage, size or type is selected. 

What should you look for in a boiler installer?

When investing in a new boiler, the installation process must be as precise and professional as the technology. An improperly installed boiler can lead to inefficiencies, malfunctions, and even safety hazards. To ensure you’re hiring a reliable and skilled boiler installer, consider the following factors:

  • Accreditations: A reputable boiler installer should be Gas Safe registered. Many manufacturers also offer their own accredited installer schemes, which may provide an extended warranty. 
  • Experience: Years of hands-on experience can be invaluable, and an installer who’s been installing home heating systems for a long time will likely have encountered and overcome a variety of installation challenges.
  • References and reviews: Word of mouth or reliable online reviews are often the best indicators of a professional’s quality of work.
  • Comprehensive service: Beyond the installation, it’s beneficial to find an installer who also offers after-sales service, maintenance, and repairs.
  • Clear quotes: A reliable installer should provide transparent, itemised quotes that detail labour costs, parts, and any other potential expenses.
  • Warranty: Check if the installer offers a guarantee or warranty on their work.

Frequently Asked Questions

Our methodology

This research was conducted and then analysed using a scoring system based on the most important considerations consumers would take into account when choosing a boiler based on their needs. 

Each combi boiler was rated on its ability to deliver against these factors. We also analysed hundreds of independent consumer reviews found on third-party review sites, testimonials, marketing materials and independent journals and media coverage. Each combi boiler was given a score out of 100.

Companies were rated according to:

  • The power outputs of each boiler with a total score of 12; 
  • The energy grade or efficiency of each boiler, with a total score of 12;
  • The sound power of each boiler with a total score of 12;
  • The weight of the boiler with a total score of 12;
  • The guarantee/warranty period for a total score of 5;
  • The years of experience of the boiler manufacturer for a total score of 7 – 10; 
  • The average price of the combi boiler with a total score of 3;
  • The reputation of the company on review sites like Trustpilot, with one point given to each star; 
  • Additional benefits include whether or not hot water storage is included in the boiler (2 points), whether a controller is present (3 points), whether or not the boiler is a ‘smart boiler’ and works with Alexa, Google etc. (2 points) and whether or not 24/7 customer support is available (4 points).