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Upgrading your boiler can be a game-changer for homeowners, with the best combi boilers slashing your household bills and ensuring an energy efficient central heating system that delivers hot water on demand.
Combination boilers eliminate the need for a water tank, reduce carbon emissions, and are compact enough to fit in a cupboard. While the cost of a new boiler can be around £1,900, cutting annual energy bills by up to £540 means it soon pays for itself, making them a popular choice for homeowners.
Our experts have compared 65 combi boilers, assessing power output, price, manufacturer reputation, and customer reviews, helping you choose the best new boiler for your home.
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Our reviews team only recommends products and services we believe provide value in the lives of our readers. We’ve spent hundreds of hours conducting in-depth research on combi boilers to give you the most accurate reviews and advice.
During our research, we consulted with industry experts, including fitters and industry insiders, some of which is contained within this guide.
To compile our reviews and list of recommended boilers, we’ve compared dozens of the best combi boilers available in the UK, as well as reading hundreds of Trustpilot reviews and customer feedback.
We have focussed on boiler brands that are:
Read more about our boiler review and research process.
| Best for | Power output (kW) | Water flow rate (litres/min) | Size (volume in litres) | Price | |
|---|---|---|---|---|---|
| Worcester Bosch Greenstar 38CDi Classic Combi Boiler | All-around combi boiler | 30 | 16.4 | 119 | £1,559.99 |
| Ideal Heating Vogue GEN2 Combi C32 Gas Boiler | Small homes | 26 | 13.1 | 109 | £1,152.99 |
| Viessmann Vitodens 200-W | Large homes | 32 | 17 | 113 | £1,779.99 |
| Vaillant ecoTEC 835 exclusive with green iQ | Most powerful | 35 | 14.5 | 129 | £1,778.98 |
| Baxi Duo-Tec 33 Gas Combi Boiler | Affordable price | 28 | 13.5 | 121 | £1,075 |
| EHC Fusion Mercury 26kW 3-Phase Electric Combi Boiler | Greener option | 26 | 12 | 80 | £1,440.99 |
A combi boiler provides central heating and hot water for your home. It works by heating water directly from the mains, so that when the water reaches your taps and shower it only takes a short while to heat up. There’s also no need for a separate hot water storage tank or cylinder, which is what makes the combi boiler a good choice for smaller homes. Over 80% of boilers in the UK are combi boilers, which makes them the most popular.
A combi boiler has two water circuits in it. One is a pumped loop to the central heating that circulates the water through the emitters (radiators or underfloor heating); the other is for the hot water, where the water is passed through a heat exchanger and heated as it passes. Most combi boilers have two separate heat exchangers – one for central heating and the other for hot water – and there is a diverter valve that switches between the two depending on whether the unit is delivering hot water or central heating.
In hard-water areas, these diverter valves can become blocked and ‘stick’ in one position. The other issue with hard water is that it can also potentially block the hot water heat exchanger, causing it to become less effective, or sometimes the water boils and causes banging noises. Some combi boilers now have two separate pipes through the same heat exchanger so there is no need for the diverter valve. This simplifies the system, but you still need to be aware of the pipes potentially furring up.
A combi boiler can be gas or electric, but in the UK most homeowners opt for gas. This is mostly down to the fact that gas boilers are more readily available in the UK market and, subsequently, this makes them a more affordable option over electric.
For homeowners that aren’t connected to the grid, LPG (liquefied petroleum gas) or oil combi boilers are a good option. Oil boilers work similarly to gas and many combi boilers have models for both gas and oil. LPG boilers are another alternative for off-grid homeowners. LPG is made from a mixture of gaseous hydrocarbons taken from natural gas, oil extracting and oil refining. It works the same way as a gas or oil boiler would.
Here’s how gas combi boilers compare to electric combi boilers.
| Gas combi boiler | Electric combi boiler |
|---|---|
| Cheaper to run | Expensive to run (energy price cap may increase) |
| Hot water is heated directly from the tap | Modern A-rated electric combi boilers have an energy efficiency of 99% or higher |
| Burns fossil fuels | Can be powered by carbon-free electricity |
| Most common combi boiler in the UK | Less common boiler type in the UK |
When installing a new combi boiler, it’s important to consider the cost. Although there are lots of factors that will impact the exact cost, we’ve calculated the average price.
Based on our research, the below table reflects the average cost of a combi boiler in the UK in 2024.
| Boiler type | Average combi boiler cost | Average combi boiler installation price | Average cost of combi boiler including installation |
|---|---|---|---|
| Combi boiler | £1,200 | £400 – £2,000 | £1,600 – £3,200 |
There’s plenty to consider when choosing the right combi boiler for your home, and there’s a lot that will affect the cost, too.
One of the biggest advantages of installing a new A-rated combi boiler is how much you can save on your energy bills. Homeowners can shave up to £540 off their energy bills per year, but the exact amount you’ll save will depend on your house size, location and energy rating.
Based on October’s energy price cap, this is how much you can save on your energy bills by installing a new combi boiler, according to Energy Saving Trust.
| Property type | Energy rating D (78-82%) | Energy rating E (74-78%) | Energy rating F (70-74%) | Energy rating G (<70%) |
|---|---|---|---|---|
| Bungalow | £180 | £200 | £225 | £320 |
| Flat | £75 | £80 | £95 | £124 |
| Mid-terrace house | £165 | £185 | £205 | £295 |
| Semi-detached house | £200 | £225 | £250 | £355 |
| Detached house | £245 | £300 | £380 | £540 |
Figures based on fuel prices as of October 2023
Modern A-rated combi boilers have a lifespan of between 10 to 15 years. This type of boiler is energy efficient, eco-friendly and should see you saving on your energy bills. However, factors like brand, model and general maintenance of your combi boiler system will affect how long it lasts.
Although combi boilers last between 10 to 15 years, they can of course last well beyond that if they’re well maintained. This can make it tricky for homeowners to know exactly when to replace their boiler, especially if it’s still functioning. Here are some warning signs that you may need to replace your combi boiler.
What to look out for:
We’ve reviewed the best boiler manufacturers in the UK and compared their combi boilers according to price, power output, water flow rate and warranties. Different homes have different heating and water flow requirements, which are relative to household size. We’ve found the best options for small and large homes, as well as an all-around boiler to suit the average UK home.
To find the most suitable boiler for your needs, there are certain elements to compare. Firstly, the heating output is how much energy your boiler can put into heating your home and hot water. The water flow rate measures how many gallons of hot water could come out of your taps and shows per minute.
Based on our research, which compared seven brands and 65 models, these are the best combi boilers to choose for your home.
Specifications
Warranty: 5 years standard or up to 10 years when installed by a Worcester Accredited Installer | Energy efficiency rating: A | Output rating (kW): 30 | Water flow (litres/min): 16.4 | Size (mm): 750 x 440 x 360 | Price: £1,559.99
Worcester Bosch is one of the UK’s market-leading boiler manufacturers. It has a large range of combi boilers for small to large homes that come with A-rated energy efficiency.
After thoroughly comparing energy efficiency, heating output, price and water flow rate, we’d recommend the Worcester Bosch Greenstar 38CDi Classic Combi Boiler as the best all-around choice for most people.
Heating output
The average UK home with three or four bedrooms has around 10 radiators. For this number of radiators, your boiler’s heating output should be between 28kW to 34kW, and so the Greenstar 38CDi’s maximum heating output of 30kW should comfortably heat homes with up to 15 radiators.
Water flow rate
It’s becoming common for UK homes to have more than one bathroom or an en-suite, which often means there are two showers in the house. Running a shower is a big drain on the flow rate of a combi boiler. The average home needs around 12l per minute, whereas the Greenstar 38CDi has a water flow rate of 16.4l per minute. A water flow rate of 15 or more is considered good and enables you to use multiple taps or showers at the same time.
Controls
The Greenstar 38CDi doesn’t come with smart controls, but it does still offer some level of advanced heating control. There’s an option for holiday mode, which allows you to programme your central heating in a way that suits your schedule. Other controls include a pre-heat mode to get hot water faster and an eco mode for energy saving.
Warranty
The manufacturer offers a five-year warranty as standard, or up to 10 years if your combi boiler is installed by a Worcester Accredited Installer. Worcester Bosch has an impressive 4.6-star rating on Trustpilot, with customers praising the fast service received and highly energy-efficient products.
Price
A new boiler can be a costly investment. However, it’s not always wise to choose the lowest-costing combi boiler on the market since you might lose out on desired features. The Worcester Bosch Greenstar 38CDi Classic Combi Boiler is a fair price considering it has a high heating output and water flow rate.
| Worcester Bosch Greenstar 38CDi Classic Combi Boiler | |
|---|---|
| Average cost excluding installation | £1,559.99 |
| Average installation cost | £400 – £2,000 |
| Total cost | £1,959.99 – £3,559.99 |
For our choice of the best all-around combi boiler, we looked for the boiler that could power small-, medium- and large-sized homes. This combi boiler also needed a water flow rating of 12l or higher to suit homes with more than one bathroom, and it needed to be priced below £1,600.
Specifications
Warranty: 10 years | Energy efficiency rating: A | Output rating (kW): 26 | Water flow rate (litres/minute): 13.1 | Size (mm): 740 x 445 x 330 | Price: £1,152.99
Choosing the right boiler for your size of home has much to do with how many radiators and bathrooms your home has. The Ideal Vogue GEN2 Combi C32 Gas Combi Boiler is a good fit for small homes with up to 10 radiators and only one bathroom.
Heating output
The Ideal Vogue GEN2’s maximum central heating output is 25kW, which is well within the recommended range for a small home of 24kW to 27kW. This power output is suitable for homes with up to 10 radiators. Some small homes could have more radiators, so it’s best to check your radiator count and compare this to the power output when deciding which boiler to buy.
The Ideal Vogue GEN2 is manufactured in the UK and features an LCD screen with a full-colour display so that it is easy to use. This combi boiler received Good Housekeeping Recommended Status in 2013 and 2017, though it is more affordable than most others on the market with similar features.
Water flow rate
Water flow rate is an essential factor to consider when choosing a combi boiler. The Ideal Vogue GEN2’s flow rate of 13.1l per minute surpasses the necessary requirements for a small home. Small homes require between six and 12l per minute according to Water Filter Spot.
Controls
The Ideal Vogue GEN2 has more than one way to control your central heating. You can monitor your central heating and hot water consumption through the Ideal Heating Electronic Thermostat, which can be purchased separately. The RF electronic thermostat allows you to programme your combi boiler system to turn on when it suits you best and control the temperature.
The Ideal Heating Weather Compensation kit works by measuring the temperature outside your home and adjusting the temperature of your radiators. This could be an add-on you’d like to consider if you’re concerned with keeping energy bills low.
Warranty
The Ideal Vogue GEN2 comes with an eight-year warranty as standard, or a 10-year parts and labour warranty when installed with an Ideal System Filter. Compared to other brands like Worcester Bosch, which offers five years as standard and Viessmann, which offers seven years, Ideal Heating’s warranty is one of the best on the market.
Compared to similar models that would also be well-suited for small homes, the Idel Vogue GEN2 is the better option. Viessmann’s Vitodens 200-W 25kW only offers a five-year warranty and Vaillant offers a mere two-year warranty ecoFIT Pure 825.
Ideal Heating also receives an outstanding 4.8-star rating on Trustpilot, which is higher than a lot of other leading boiler manufacturers in the UK.
Price
Ideal Heating Vogue GEN2 is one of the best combi boilers on the market for smaller homes that can avoid paying out for higher heating outputs. Compared to other similar combi boilers, Ideal Heating’s price is fair and we consider it to be good value for money.
| Ideal Heating Vogue GEN2 Combi C32 Gas Boiler | |
|---|---|
| Average cost excluding installation | £1,152.99 |
| Average installation cost | £400 – £2,000 |
| Total cost | £1,552.99 – £3,152.99 |
To choose the most suitable combi boiler for small homes, we looked for one with a heating output that was somewhere between 24kW and 27kW. The water flow rate also needed to be between six to 12l per minute and the combi boiler had to be priced below £1,200, which is the average price of a combi boiler.
Specifications
Warranty: 7 years | Energy efficiency rating: A | Output rating (kW): 28 | Water flow rate (litres/minute): 13.5 | Size (mm): 780 x 450 x 345 | Price: £1,075
If you’re on a budget, or simply don’t want to overspend unnecessarily on your new combi boiler, then we recommend the Baxi Duo-Tec 33 Gas Combi Boiler. This combi boiler is marketed at an affordable price yet doesn’t compromise on energy efficiency, central heating output, or product warranty.
Heating output
The Baxi Duo-Tec is manufactured in the UK, and has a maximum central heating output of 28kW, so it is ideal for both small and medium sized-homes with more than one bathroom and up to 15 radiators. This is one of the main reasons why we’ve chosen this combi boiler – for the price, this boiler suits a wide range of homes.
For homeowners with smaller homes, space is something to consider when choosing a new combi boiler. Although the Baxi-Duo Tec has a sizeable capacity, at (h)780mm x (w)450mm x (d)345mm, it is still compact enough to fit inside a cupboard or be attached to your kitchen wall without intruding into the floor plan too much.
Water flow rate
At 13.5l per minute, the Baxi’s water flow rate is well within the average household’s requirements and should see your household capable of running multiple taps and showers at the same time. The Baxi Duo-Tec comes with a seven-year standard manufacturer guarantee; whilst it isn’t the longest warranty on the market, its other features far outweigh this.
Controls
The Baxi Duo-Tec 33 is compatible with the uSense thermostat. Through the Baxi uSense app, users can control heating, set times for their heating to switch on and even check boiler fault diagnosis.
It’s also hydrogen-ready, so you won’t need to replace your boiler if the UK decides to switch to hydrogen as its main heating fuel.
Baxi receives a trustworthy 4.6-star rating on Trustpilot, with mostly good customer reviews. The positive customer reviews recommend Baxi as installers for being timely and the products for being reliable.
Price
Baxi offers extremely competitive pricing on its boilers considering its high-end features like its uSense controls. The exact price you’ll pay may vary depending on the location of your combi boiler, add-ons and if you need to relocate your boiler. Installation costs will also vary for different parts of the UK.
| Baxi Duo-Tec 33 Gas Combi Boiler | |
|---|---|
| Average cost excluding installations | £1,075 |
| Average installation cost | £400 – £2,000 |
| Total cost | £1,475 – £3,075 |
Our choice of affordable combi boiler needed to be priced below £1,200, which is the average price of a combi boiler. It also needed to be suitable for small and medium-sized homes, so above 27kW for its heating output was a must. It also needed to have a water flow rate above 12l per minute.
Specifications
Warranty: Up to 12 years extended warranty available | Energy efficiency rating: A | Output rating (kW): 32 | Water flow rate (litres/minute): 17 | Size (mm): 700 x 450 x 360 | Price: £1,799.99
For larger homes, you’ll need a powerful combi boiler that can cope with multiple showers and taps in use at the same time. The Viessmann Vitodens 200-W is our recommended choice for larger homes with more than one bathroom.
Heating output
The Viessmann 200-W has a maximum output rating of 32kW, so it can easily heat homes with up to 20 radiators with ease. This combi boiler is ideal for medium to large-sized homes with over three bedrooms. Even though the Viessmann Vitoden 200-W has a large capacity, it can still be wall-mounted in your kitchen or bathroom and is a very compact size of (h)700mm x (w)450mm x (d)360mm.
Water flow rate
It’s also good for detached homes with two or more bathrooms since the water flow rate for this premium combi boiler is relatively high. With a water flow rate of 17l per minute, you can expect a good hot water supply to taps and showers even when they are used simultaneously.
Viessmann receives a four-star rating on Trustpilot and customer reviews have praised the brand for its boilers being reliable. The Viessmann 200-W is also future-proof and ready for any new UK legislation on fuel types, as it comes hydrogen-ready.
Controls
This combi boiler is incredibly easy to use, and it even comes with smart controls. The wifi-enabled controls can be managed via the Viessmann app, which allows you to monitor energy consumption, change temperature and turn on your heating before you arrive home. As well as this, the Viessmann 200-W is complete with a seven-inch colour touchscreen display that is very user-friendly.
Price
Although the Viessmann Vitodens 200-W is recommended for larger homes and comes with a much higher output than most, and that’s why its price is above average for a combi boiler. For the premium features like smart control and touchscreen interface, Viessmann has been fair with pricing.
| Viessmann Vitodens 200-W | |
|---|---|
| Average cost excluding installations | £1,779.99 |
| Average installation cost | £400 – £2,000 |
| Total cost | £2,179.99 – £3,779.99 |
Our choice of combi boiler for larger homes needed to have a heating output of 32kW or more as well as water flow rate higher than 15l per minute. The price wasn’t as important here, as homeowners should expect to pay more for larger-capacity combi boilers.
Specifications
Warranty: Up to 10 years | Energy efficiency rating: A | Output rating (kW): 35 | Water flow rate (litres/minute): 14.5 | Size (mm): 720 x 440 x 406 | Price: £1,778.98
Vaillant is the second largest boiler manufacturer in Europe and is best known for its environmentally friendly products. The Vaillant ecoTEC 835 exclusive with green iQ is hand-built in Vaillant’s Derbyshire manufacturing plant and is a powerful combi boiler that would suit medium- to large-sized homes.
This modern A-rated combi boiler is integrated with Vaillant’s unique green iQ technology, which makes this one of the most energy-efficient combi boilers on the market with low fuel consumption and low running costs.
The Green iQ mode optimises running cycles, which results in lower gas consumption, and the boiler is highly recyclable at the end of its lifespan.
Heating output
The Vaillant ecoTEC 835 comes with a large heating output capacity of 35kW. This means that the ecoTEC 835 is best-suited to homes with more than 15 radiators, or typically homes with three or more bedrooms.
Water flow rate
Vaillant ecoTEC 835’s water flow rate of 14.5l per minute is powerful enough to supply hot water on demand to multiple taps and showers when required. This is another reason we’d recommend this combi boiler as the most powerful and consider it to be a good choice for homes with more than one bathroom.
Controls
Vaillant is a manufacturer concerned with the environment and keeping energy bills low. Its vSMART technology gives you the ability to control your boiler from your smartphone or tablet so that you can monitor energy consumption at all times, whether you’re at home or not. As well as this, the ecoTEC 835 can adapt itself, so it’s always giving you the exact amount of heat you need.
Vaillant prides itself on working towards low-carbon solutions. All of its boilers have been tested with 20 per cent hydrogen with natural gas as part of the HyDeploy Project.
Vaillant receives a 4.4-star Trustpilot rating, with many customers praising the company for quick installation and the long guarantee. The ecoTEC 835 also benefits from up to 10 years’ guarantee when you book a Vaillant Advance installer.
Price
Vaillant’s ecoTEC 835 is the least expensive model with these specifications and high-end features like the vSMART controls.
| Vaillant ecoTEC 835 exclusive with green iQ | |
|---|---|
| Average cost excluding installations | £1,778.98 |
| Average installation cost | £400 – £2,000 |
| Total cost | £2, 578.98 – £3,778.98 |
Our choice of most powerful combi boiler needed to have a heating output of above 32kW. It was also important for this type of boiler to have a long warranty since the price is higher than the average. Having smart controls was a must, as a powerful combi boiler like the ecoTEC 835 that’s meant for larger homes could expend a lot of unnecessary energy if not monitored carefully.
Specifications
Warranty: 5 years | Energy efficiency rating: D | Output rating (kW): 26 | Water flow rate (litres/minute): 12 | Size (mm): 690 x 451 x 258 | Price: £1,440.99
As the UK moves towards greener energy sources, home appliances like boilers that we install in our homes may come under scrutiny. Although gas is currently the most common fuel type used in the UK, electric combi boilers can be a greener option but this also depends on if you’re using solar panels or on a green energy tariff.
The Electric Heating Company’s (EHC) Fusion Mercury 3-Phase electric combi boiler is ideal for small homes. It also provides a cost-effective alternative for homes that are off-grid and may have otherwise installed an LPG or oil boiler.
Water flow rate
The EHC Fusion Mercury 3-Phase is best suited to homes with one bathroom. This type of combi boiler has a low water flow rate, which would make it difficult to have more than one shower. The EHC Mercury 3-Phase’s water flow rate of 12l per minute should be enough to supply hot water on demand for a household with average water usage.
Energy efficiency
Compared to gas boilers, you’ll notice that an electric option – at first glance – doesn’t appear to be worth the investment. Typically, electric combi boilers are D-rated, so compared to a gas boilers’ A-rating there’s quite a difference. The main reason for this is due to running costs. Electric combi boilers are far more expensive to run than gas combi boilers, and even more so now in the midst of a cost of living crisis.
If you’re looking to pair an electric combi boiler with solar panels then this is possible but tricky to do due to the fact that people tend to mostly use hot water first thing in the morning or at night when solar production is generally at its lowest. To go this way, you’d need to invest in a solar battery to store and use your solar energy when the sun isn’t out.
Heating output
The EHC Fusion Mercury has a heating output of 26kW, which makes it an ideal choice for small homes with up to 10 radiators. At the top end of the required heating output for a small home, the EHC Mercury 3-Phase is a good choice and is certainly capable of heating your home and coping with average water usage.
Price
Electric combi boilers tend to be more expensive than gas combi boilers, partly because they are less common. For this reason, it may not seem like EHC’s Mercury 3-Phase is a fair price when compared to similar gas combi boiler models.
| EHC Fusion Mercury 26kW 3-Phase Electric Combi Boiler | |
|---|---|
| Average cost excluding installations | £1,440.99 |
| Average installation cost | £400 – £2,000 |
| Total cost | £1,840.99 – £3,440.99 |
To choose the best electric combi boiler, we compared heating output, water flow rate and price. A lot of them tend to have low outputs and flow rates, so we chose the best combination for the most reasonable price.
One of the most important things to consider when installing a new combi boiler is which size is right for your home. It’s a significant investment that you will rely on to heat your home and supply hot water. It certainly isn’t a one-size-fits-all situation, and the general rule is the larger your home, the higher the kW of the boiler you’ll need.
Things to consider:
One of the easiest ways to decide which size would suit your home is to count the number of radiators that you have. The more radiators, the more power your boiler will need to heat your home.
Water flow rate is also something that you may want to consider when choosing the right boiler, especially if you have more than one bathroom. The average UK home requires a water flow rate of between six and 12l per minute. If you have more than one bathroom, choosing one with more than 12l per minute would be best suited.
Despite the many benefits of a combi boiler, there are some downsides, especially if you have a large home or live in an area with low water pressure. They aren’t best suited to homes with low water pressure since they rely on good mains pressure to supply hot water to the entire house. If multiple taps are on, the water pressure drops considerably.
Combi boilers can be powered by natural gas or electricity. Currently, in the UK, most combi boilers are powered by gas since they are more readily available and a lot cheaper to run than electric boilers. However, new legislation in the UK could mean that as of 2025 there will be no new gas boilers in new-build homes. This means any new builds built after this time will have either electric-powered boilers or alternative heating sources such as heat pumps. It’s important to note, though, that Prime Minister Rishi Sunak has announced a consultation on this legislation to determine if the deadline should be pushed back to 2035, which is the point at which no new gas boilers can be sold in the UK.
Combi boilers are ideal for small- to medium-sized homes, and some are designed specifically for larger homes with multiple bathrooms, but it may not be the best choice for very large homes. For homes with multiple bathrooms, and in particular multiple showers, some will struggle to meet the hot water demand requirements, so it’s essential to install a suitably-powerful boiler in these cases.
The average cost for installing a new boiler in the UK 2024 is between £400 and £2,,000. The type of boiler, changing the location of your boiler in your home, how long installation takes and changing fuel type are all things that may affect your household’s installation cost.
A combi boiler has an average lifespan of 10 to 15 years, but it can last well beyond this. Although combi boilers may last longer than the proposed lifespan, as they age their energy efficiency decreases. Modern A-rated boilers operate at 90 per cent, while older G-rated boilers operate at just 70 per cent, costing a lot more to run. Installing a new A-rated combi boiler can save you up to £840 on your energy bills per year.
Installing a new combi boiler should take between one to three days. There are factors that can affect exactly how long it takes, including:
Installing a new combi boiler can be an expensive investment. Depending on your circumstances, you may be eligible for funding to help with the costs associated with energy-efficient home improvements.
The Energy Company Obligation’s ECO4 scheme is designed to help vulnerable households with the initial costs of home improvements, and this includes new boilers.
To qualify you would need to receive one of the following:
Combi boilers provide both central heating and hot water supply to our taps and showers. The domestic hot water should be kept on all the time in order to provide a constant supply of hot water. Your central heating does not need to be kept on all the time, and doing so could increase your energy bills. Combi boilers come with a timer, which means you can set your central heating to come on at times that suit your schedule.
