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Best Combi Boilers of 2025: Top Models Reviewed

Best Combi Boilers of 2025: Top Models Reviewed
Patrick Garner

Patrick GarnerGas Safe Engineer & Installation Manager

Updated 16th Apr, 2025

Looking for the best combi boiler in 2025? At Heatable, our team of Which?-approved gas engineers has reviewed and ranked the top models based on efficiency, reliability, and value.

Drawing on our experience installing over 50,000 boilers across the UK, we’ve curated this guide to help you find the perfect combi boiler for your home, whether you’re after the best all-around option, the most budget-friendly, or the most efficient.

Our Top 3 Best Combi Boilers for 2025

Here’s a quick look at our top picks for the best combi boilers in 2025:

What is a Combi Boiler? 

Combi boilers are the most popular type of boiler in the UK, primarily because they provide both heating and hot water from a single, compact unit. Ideal for most homes, combi boilers are efficient and space-saving solutions.

Prefer video? Check out our YouTube video review of the best combi boilers:

What Makes a Combi Boiler the Best?

The best combi boilers excel in:

  • Efficiency: High ratings (e.g., 98% efficiency) save on energy costs.

  • Reliability: Long warranties and strong customer reviews signal durability.

  • Value: Balances upfront cost with long-term savings.

  • Aftercare: Quality support ensures peace of mind.

How We Chose the Best Combi Boilers for 2025


Our selection process, led by expert gas engineers, evaluated:

  • Warranty Period: Longer warranties indicate manufacturer confidence.

  • Efficiency Ratings: Higher ratings mean lower bills.

  • Customer Reviews: Insights from 10,000+ homeowners via Which? surveys.

  • Brand Reputation: Awards like the Which? Best Buy signal quality.

  • Aftercare Services: Reliable maintenance support.

  • Price vs. Value: Balancing cost with performance.

Best Combi Boilers of 2025: Detailed Reviews

Below is our carefully curated selection of the best combi boilers from top UK manufacturers.

These models stand out for their exceptional customer reviews, long warranties, technical superiority, energy efficiency, robust heating capabilities, and award-winning aftercare support.

We prioritised brands with industry-leading support, as reliable aftercare is crucial when issues arise.

#1 Worcester Bosch Greenstar 4000 – Best All-Around Combi Boiler

Worcester Bosch Greenstar 4000

Key details:

  • Warranty: 10 years (via Heatable)

  • Efficiency: 94% (A-rated)

  • Output: 25–30 kW

  • Flow Rate: 10.5–12.3 L/min

  • Price: From £1,152.99

Why It’s the Best: The Worcester Bosch Greenstar 4000 is our top pick for 2025, thanks to its 14 consecutive Which? Best Buy Awards, a 4.7/5 Trustpilot rating (17,000+ reviews), and smart home compatibility with Hive, Nest, and tado°. It’s quiet, compact, and perfect for small to medium homes.

Pros:

  • Quieter than many competitors, ideal for noise-sensitive environments.

  • Works with popular smart home systems like Hive, Nest, and tado°.

  • 10-year parts and labour guarantee through Heatable.

  • Excellent customer support and aftercare services.

  • Small footprint, fits easily in tight spaces.

Cons:

  • It is more expensive upfront compared to budget models like Alpha or Ideal.

  • Best suited for small to medium-sized homes, not ideal for large homes.

  • Lacks some of the advanced diagnostics features found in Viessmann models.

Worcester Bosch 4000 Boiler Install

The image above shows a Worcester Bosch 4000 installed by the Gas Safe engineers here at Heatable. Get your free quote from us here.

"The aftercare service offered by the manufacturer is a key factor in choosing a new boiler as you want to know they will be fixed promptly without any issues". - Allen Hart, Gas Safe Engineer.

Prefer video? Watch our comprehensive breakdown of the Worcester Bosch 4000 in our YouTube video with Gas Engineer Allen Hart below:

#2 Viessmann Vitodens 100-W – Most Efficient Combi Boiler

Viessmann Vitodens 100-W

Key details:

  • Warranty: 12 years (via Viessmann-trained engineers)

  • Efficiency: 98% (A-rated)

  • Output: 26–35 kW

  • Flow Rate: Up to 14.1 L/min

  • Price: From £900

Why It Stands Out: With an industry-leading 98% efficiency, the Viessmann Vitodens 100-W saves on energy bills. It offers Wi-Fi connectivity and a stainless steel heat exchanger for durability.

Pros:

  • Includes features like Wi-Fi connectivity and smart home compatibility.

  • Stainless steel heat exchanger enhances longevity and reliability.

  • Offers up to 12 years of warranty when installed by a Viessmann-trained engineer.

  • A-rated for energy efficiency, capable of up to 98% efficiency.

Cons:

  • More expensive upfront compared to budget models like Alpha or Ideal.

  • While compact, it may still be slightly larger than some other models, limiting placement options.

  • Fewer output ratings compared to some other models.

  • Advanced features may require a more knowledgeable user or a professional setup.

Viessmann Vitodens 100-W Installation

The image above shows a Viessmann Vitodens 100-W installed by the team here at Heatable. Get a free quote from us here.

"What sets it apart is its impressive connectivity, allowing for remote access to the boiler, performance monitoring, and the ability to diagnose potential faults. This feature is a significant advantage not only for businesses but, more importantly, for our valued customers.” - Phil Cox, former Director of Sales, British Gas.

#3 Worcester Bosch Greenstar 2000 – Best Value for Small Homes

Worcester Bosch Greenstar 2000

Key details:

  • Warranty: 6 years (extendable)

  • Efficiency: 94% (A-rated)

  • Output: 25–30 kW

  • Flow Rate: Up to 12 L/min

  • Price: From £750

Why It’s Great: The Greenstar 2000 is Worcester Bosch’s quietest and most affordable model, designed for small homes. Its compact size fits in kitchen cupboards, and it’s backed by Worcester’s strong reputation.

Pros:

  • Lower upfront cost compared to other Worcester Bosch models like the 4000.

  • Slim and compact, making it suitable for small spaces like kitchen cupboards.

  • Operates quietly, making it ideal for smaller homes or flats.

  • Backed by Worcester Bosch’s strong reputation for reliability.

Cons:

  • Standard 5-6 year warranty, which is shorter than the 10-year warranty offered by higher-end models.

  • Lacks some of the advanced features and smart technology compatibility found in more expensive models.

  • Lower water flow rate compared to more powerful models like the Worcester Bosch 4000.

  • Less comprehensive aftercare options compared to premium models.

#4 Vaillant EcoTec Plus – Best for Larger Homes

Vaillant ecoTEC Plus Boiler

Key details:

  • Warranty: 10 years (via Heatable)

  • Efficiency: 94% (A-rated)

  • Output: 25–38 kW

  • Flow Rate: Up to 15.9 L/min

  • Price: From £1,100

Why It’s a Top Pick: The Vaillant EcoTec Plus offers powerful performance for larger homes, with a high flow rate and Quiet Mark certification for low noise.

Pros:

  • Ideal for larger homes, offering powerful heating and hot water output.

  • ErP A-rated for both heating and hot water efficiency.

  • Quiet Mark certified, ensuring low noise levels.

  • Compatible with vSMART technology for remote control.

Cons:

  • More expensive than budget models like Alpha E Tec NX or Ideal Logic+.

  • Lacks the advanced diagnostic features found in Viessmann Vitodens models.

  • It may be more powerful than needed for smaller properties, leading to inefficiency.

  • Larger in size compared to Worcester Bosch Greenstar 4000, making it harder to fit in tight spaces.

Best Combi Boiler Quote


#5 Alpha E-Tec NX – Most Affordable Combi Boiler

Alpha E Tec NX Boiler

Key details:

  • Warranty: 10 years (via Heatable)

  • Efficiency: 93% (A-rated)

  • Output: 26–33 kW

  • Flow Rate: Up to 14.1 L/min

  • Price: From £700

Why It’s a Great Value: The Alpha E-Tec NX combines affordability with quality, featuring a stainless steel heat exchanger and a slim design.

Pros:

  • Lower upfront cost compared to premium models like Vaillant or Worcester Bosch.

  • Slim design, making it easy to fit in small spaces like kitchen cupboards.

  • Stainless steel heat exchanger enhances durability compared to aluminium.

  • Up to 10 years, offering good coverage for peace of mind.

Cons:

  • Less established than top-tier brands like Worcester Bosch or Vaillant.

  • Fewer output options (26 and 33 kW) compared to other brands.

  • Lower flow rate compared to more powerful models like the Vaillant EcoTec Plus.

  • Lacks some of the advanced technology found in higher-end models.

Comparison Table: Best Combi Boilers of 2025

Model

Best for

Efficiency

Output (kW)

Flow Rate (L/min)

Warranty

Price

Which? Award

Worcester Bosch 4000

All-Around

94%

25-30

10.5–12.3

10 years

£1,152.99+

Yes

Viessmann Vitodens 100-W

Most Efficient

98%

26-35

Up to 14.1

12 years

£900+

Yes

Worcester Bosch 2000

Small Homes

94%

25-30

Up to 12

6 years

£750+

Yes

Vaillant EcoTec Plus

Large Homes

94%

25-38

Up to 15.9

10 years

£1,100+

No

Alpha E-Tec NX

Budget Friendly

93%

26-33

Up to 14.1

10 years

£700+

No

Why You Might Not Need the Best Combi Boiler

While top models offer great features, a mid-range boiler can suffice if:

  • You have a small home with low hot water needs.

  • Budget is a priority - models like the Alpha E-Tec NX offer great value.

  • Proper installation and maintenance can make even a budget boiler perform well.

Next Steps For Your New Boiler Journey:

When planning to install a new boiler for your home, there are several important factors to consider. Make sure to refer to the following guides to help you make informed decisions:

To dive deeper into these topics, head over to our advice section or check out our YouTube channel to learn more.

Get a Quote for a New Combi Boiler Today 

If you’re aiming to get the best deal on a new boiler, consider getting a quote from us. Here’s why:

  • Gas Safe installation within 24 hours.

  • Thousands of satisfied customers with an average score of 4.9 on Trustpilot, surpassing the market leader.

  • Which? Trusted Trader: Heatable is proudly recognised as a Which? Trusted Trader.

  • Price match guarantee: We will match any like-for-like cheaper quote.

  • Flexible payment options, including interest-free finance*.

  • Up to a 12-year guarantee on selected boilers.

  • Fixed price guarantee: No hidden costs.

  • Save your quote and decide later.

  • Get an instant fixed price on a new boiler here.

To learn more about boilers, visit our advice section, check out our YouTube channel, or read customer testimonials here.

Heat Happy.

FAQ's

While we won’t endorse any specific brand, we highly recommend checking customer reviews on reputable third-party platforms and consulting results from annual boiler surveys. These sources provide unbiased insights and can help you make a more informed decision when choosing the right boiler for your needs.

Worcester Bosch models, like the Greenstar 4000, are renowned for reliability, backed by 14 Which? Best Buy Awards.

The Worcester Bosch Greenstar 2000 is ideal for small homes due to its compact size, quiet operation, and affordability.

Are you unsure whether you should choose a combi boiler or a system boiler?  The biggest factor in determining whether you will need a combi or a system boiler is your home's hot water demands.  Are multiple bathrooms going to be used at the same time? The system is advised... If you have a growing family and are likely to be using multiple bathrooms simultaneously, then a system boiler is likely the way to go.  However, for most other circumstances, a combi boiler is advised... Why?  They have a range of power options  Extremely efficient  Easy to repair and maintain  No other components are at risk of failing 
Combination boilers are the most popular type of domestic boiler in the UK.  However, they may not be suitable for larger homes with multiple bathrooms and showers, where they often struggle to maintain adequate water pressure to multiple outlets.  Additionally, they may not be suitable for areas that suffer from low mains water pressure. In such circumstances, regular or system boilers are often advised instead. 
The cost of a new central heating boiler is dependent on a variety of different factors, these include the following: The type of boiler you have installed e.g. fitting a combi, regular or system. The boiler model you choose e.g. mid or premium range. If you want to relocate your boiler e.g. from the garage to the attic. If you want to convert your boiler e.g. from regular to combi.  Any add-ons you purchase e.g. magnetic filters, smart controls etc. One of the most common and straightforward types of central heating boiler installations is a straightforward combi swap i.e. replacing your old combi with a new combi. This is much simpler than replacing a system boiler with a combi. This is due to conversions being more complex to install, taking more time, and requiring more labour and more materials. More everything. The boiler model you choose also has an impact on the cost and at Heatable we offer more value-orientated brands such as Alpha, as well as award-winning, premium brands such as Worcester Bosch and Viessmann.

Plumbers and gas engineers frequently recommend top brands such as Worcester Bosch, Vaillant, Ideal, and Glow-worm for their reliability and performance. Among these, Worcester Bosch stands out particularly due to its strong reputation in the industry.

According to the annual boiler survey by Which?, which gathers feedback from 100 engineers, Worcester Bosch has consistently been awarded the Best Buy Award for an impressive 14 consecutive years, highlighting its enduring quality and customer satisfaction.

Coldwater is fed into the combi boiler directly from the mains water supply, the gas fuel is then burned to produce heat, which is transferred from the combustion chamber to the water via the heat exchanger. Your home’s thermostat is able to detect the temperature in your home and when it detects your property's temperature has dropped, it is able to send a signal to the boiler. In response, the boiler will fire up, heat the water and pump it through the system to the radiators. Once the desired temperature has been achieved, the boiler will reduce its heat output and maintain the status quo, helping to reduce energy waste, while keeping your home warm. If someone uses a hot tap within the home, or another hot water outlet such as the shower, a component within the boiler called the diverter valve will divert hot water to the taps while they are in use. Once the tap is turned off, the diverter will be restored to the central heating position. Hot water can be directed to the central heating or the water outlets, but never both simultaneously.
If you don’t already have a combi boiler, then you might feel left out and be wondering what all the fuss is about. But we can reliably inform you that a combi boiler does indeed, live up to the hype. They provide instant hot water for both your central heating and hot water demands. You might call them a com-bi. It loves both. But it’s not just having the ease of instant hot water without having to give a giant metal tank one hour’s notice before you want a bath as though Robocop was your butler. A combi boiler is also remarkably efficient at heating the water – up to 98% efficient. We had a mathematician check this number and it’s just 2% less than 100%! That makes it superior to immersion heaters.  The efficiency offered by a combi isn’t just a lovely number though, it can make you some outrageous savings on your energy bills – savings you’ll actually notice in monetary value, not like the savings between Asda and Tesco on petrol. They’re also much kinder to the environment so the birds outside your house choking on Monster Munch packaging have one less thing to worry about. Considering underfloor heating? Read our complete guide on underfloor heating with a combi boiler. 

References

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Last updated 16 Apr, 2025

Tags: Boilers, Combi boilers, Best Combi Boilers , Most Energy Efficient Boiler , Most Reliable Combi Boiler

Patrick Garner
Written by Patrick Garner

Patrick Garner, a Gas Safe certified engineer, leads the boiler installations team at Heatable. A wealth of experience, he has successfully overseen the installation of thousands of heating systems.

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