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Best Condensing Boilers of 2021: Our Verdict

Condensing boilers are super clever, super at saving energy and super at saving money. Considering condensing? Here's the best condensing boilers of 2021.

Did you know that every year, more than 1 million new boilers are installed into UK homes?

...yep, you read that right, 1 million.

Boiler Plus Condensing Boiler That’s an incredible amount of boilers, and thanks to the introduction of ‘Boiler Plus’ legislation back in 2005, all new installs are now condensing boilers that are a huge improvement on the inefficient non-condensing models of the past. 

But what exactly is a condensing boiler? How do you know which condensing boiler to choose? 

In this guide, we’ll be answering the most frequently asked questions and help you decide exactly which boiler is best for you and your home. 

PS: We fit new condensing boilers with gas safe installation nationwide and as quick as tomorrow. Check the latest prices.

Best Condensing Boilers of 2021 (By Brand) 

Best Condensing Boilers

To determine which are the best boilers available in 2021, we considered the following factors: 

  • Warranty period offered by the brand 
  • The overall reputation of the brand based on customer reviews 
  • Trustpilot reviews  
  • Awards and accolades e.g. Which? Best Buy Awards
  • Customer service performance 
  • The price range of their boilers  
  • Efficiency ratings

Here are our top 5 best condensing boiler brands in the UK right now, in 2021:

  • #1 Worcester Bosch Combi Boilers
  • #2 Viessmann Combi Boilers
  • #3 Vaillant Combi Boilers
  • #4 Alpha Combi Boilers
  • #5 BAXI Combi Boilers


#1 Worcester Bosch Combi Boilers (Best)

Worcester Bosch Condensing Boilers

One of the UK’s most well-known and trusted boiler manufacturers, Worcester Bosch remains a favourite among installers. 

...why do we think Worcester Bosch deserve the number one spot? 

  • Which? Best Buy Award for 10-years running 
  • 10-year guarantee (when purchased via Heatable)
  • Availability of parts is second to none 
  • Excellent customer reviews and aftercare
  • High efficiency A-rated combi boilers 

Worcester Bosch Greenstar i

Worcester Greenstar i Condensing BoilerThe Greenstar i is officially Worcester's best selling combi boiler range having sold and installed more than 1 million of them in the UK alone. 

Suitable for small to medium sized homes on a budget the Greenstar i is the brand's entry level offering and the range includes the 30i i.e. 30kW and the less powerful Greenstar 25i at 25kW

Although not the brand’s best offering, it still boasts some great features, not least of which is an A-rating for efficiency, a user-friendly digital display and a reassuring 'Which?' Best Buy Award.

10 Year Guarantee Condensing Boiler

Greenstar CDi Compact Boiler 

Worcester Greenstar CDi Condensing Boiler

The CDi Compact is Worcester Bosch’s compact boiler, designed to be the ideal size to fit into small spaces, such as kitchen cupboards. 

Available with multiple power outputs including 28kW, 32kW and 36kW, this combi boiler can still provide heating and hot water for properties with varying demands, but offers the dimensions required to save as much space as possible. 

Worcester Bosch 2000

Worcester Greenstar 2000 Condensing Boiler

The 2000 is the brand's latest entry-level offering and officially the brands quietest ever boiler. It’s compact design makes it suitable for installation within small spaces such as kitchen cupboards and available within 25kW or 30kW it has enough power for flats and small homes. 

Boasting A-rating efficiency, a user-friendly digital display and a reassuring Which? Best Buy Award and a contemporary and stylish case, it’s a superb option for small property dwellers on a budget. 

Worcester Bosch 8000 Style 

Worcester 8000 Condensing Boiler

The 8000 offers the same contemporary design and feel as it's cheaper brother, the 2000 but with cutting edge features and superior power outputs, it is ideal for larger homes with more than one bathroom. 

It’s the most powerful and connected wall-hung boiler to date, capable of delivering up to 50kW's, and with optional smart technology that will top up the boiler for you when low pressure is detected.

#2 Viessmann Combi Boilers (2nd Best Condensing boilers)

Viessmann Condensing Boilers

Dominating the European boiler market, Viessmann are a relatively new entrant to the UK market, but thanks to their prestige German engineering, reliability and superb customer support they have seen huge growth and popularity within a very short period of time. 

Major benefits of Viessmann boilers include: 

  • Technically brilliant boilers e.g. they use stainless steel heat exchangers
  • 10-year guarantee (when purchased via Heatable)
  • Excellent customer reviews and aftercare
  • High efficiency A-rated combi boilers 

Viessmann Vitodens 050-W Gas Combi Boiler

Viessmann 050 Condensing Boiler

The Viessmann 050-W is the brand's entry level combi boiler, offering all of the essentials Viessmann are renowned for on a budget, including the Inox-Radial heat exchanger. 

Available with multiple size outputs including 29kW and 35kW it is suitable for small and medium sized properties, while it’s dimensions make it quite a compact size for a wall-mounted combi boiler. 

Viessmann Vitodens 100-W Gas Combi Boiler

Viessmann 100 Condensing Boiler

The Viessmann Vitodens 100-W is the best selling combi boiler from the award winning brand and has an impeccable reputation.

The boiler is an upgrade on the 050-W featuring superior internal parts and components with fewer plastic parts than the 050-W, as well as the signature stainless steel Inox-Radial heat exchanger. 

The updated 2021 model also features a new and improved stylish exterior casing, hydrogen-ready technology and an upgraded backlit LCD touchscreen display. 

The latest Vitodens 100 also includes an updated LCD touchscreen display with integrated Wi-fi, allowing you to control, diagnose the boiler and enable remote access to Viessmann support so that they can assist from afar and diagnose faults. 

Viessmann Vitodens 111-W Combi Boiler

Viessmann 111-W Condensing Boiler

If your property has high hot water demands e.g. multiple bathrooms but you don’t have the space or necessary requirements to install a system boiler with a separate hot water storage tank, the 111-W may be the solution. 

The Vitodens 111-W is a storage combi – essentially it's like a usual combi boiler – and has its own internal hot water storage tank, allowing it to deliver a ludicrous 18 litres of hot water per minute.

#3 Vaillant Combi Boilers (3rd Best Condensing Boilers)

Vaillant Condensing Boilers

Made in the UK, Vaillant is another German owned brand that has earned a reputation for reliability and high quality engineering. 

Among installers, they are credited as being one of the easiest boilers to repair. Due to their superb reputation, Vaillant is the second largest manufacturer of boilers in Europe today. 

Vaillant EcoTec Pro

Vaillant EcoTEC Pro

The EcoTec Pro is one of Vaillant’s most popular combi boilers and previously held the Which? Best Buy Award in 2016. It has been awarded Quiet Mark certification, only given to the quietest models and as ‘Eco’ name suggests, one of the brands most energy efficient boilers to date. 

Ideal for small to medium sized properties with the kW model’s coming in three different outputs to suit all, including 24kW, 28kW and 30kW along with a 2 year guarantee, with an additional 7 to 10 years available when you book a Vaillant Advance installer. 

Vaillant EcoFit Pure

Vaillant EcoFIT Pure

Similar to the Worcester Bosch CDi Compact, the EcoFit is Vaillant’s compact offering, helping to save space and is compact enough to fit in a kitchen cupboard. It’s designed to be flexible, with a rear flue option allowing you more versatility on where to install it. 

It’s also equipped with energy saving capabilities and when you don’t require so much heat, it reduces its maximum output by 20%, helping to save energy and reduce your heating bills. 

#4 Alpha Combi Boilers (4th Best Condensing Boilers)

Alpha Condensing Boilers

Alpha boilers are a recent entrant to the UK heating market, but their reputation has quickly risen to become a brand known for reliability and affordability. 

Major benefits of Alpha boilers include: 

  • Technically brilliant boilers e.g. they use stainless steel heat exchangers
  • 10-year guarantee (when purchased via Heatable)
  • Excellent customer reviews and aftercare
  • High efficiency A-rated combi boilers 

Alpha E-Tec 

Alpha ETeC Condensing Boiler

The Alpha E-Tec is Alpha Innovations most popular condensing combi boiler and although it is considered a budget-friendly brand, it uses a stainless steel heat exchanger, which is usually only seen in premium brands. 

When purchased via Heatable, the E-Tec is also offered with a very generous 10-year warranty, which is again typically only available with market leading brands, such as Worcester Bosch. 

The Alpha E-Tec is ideal for households on a budget who care about securing a combi boiler built to last. 

#5 BAXI Combi Boilers (5th Best Condensing Boilers) 

BAXI Condensing Boilers

Baxi is a British based boiler manufacturer with a lot of history and a reputation for offering excellent customer service and having a well-established nationwide network of Baxi gas installers and training centres.

Even though they are not typically viewed as a premium choice brand, Baxi does have some great condensing boilers on offer, with generous warranties and award-winning customer service. 

Major benefits of Baxi boilers include: 

  • Made in the UK
  • Excellent customer reviews and aftercare
  • High efficiency A-rated combi boilers 
  • 7 year no-quibble warranty

Baxi 600 Combi Boiler 

BAXI 600 Condensing Boiler

The Baxi 600 was engineered based on the feedback provided by installers and similar to the Worcester Bosch CDi compact, designed to be installed in small spaces. 

The Baxi 600 is available in a good selection of power outputs, ranging from 24kW to 36kW, making it an ideal boiler for small and medium sized households.

The 600 also benefits from some very innovative features including EasyFill - a spring-loaded single lever, allowing to top up the pressure easier than ever. Baxi boilers are also available with the uSense smart room thermostat, allowing you to easily control your heating via an accompanying smart phone app. 

Best Condensing Boilers (By Model) 

Best Condensing Boiler Models

The condensing boilers above are the best ranking boiler models available from each of the manufacturers in our best boiler brand rankings. 


Based on our analysis, these are by far the best models on offer by some of the UK’s most prestigious boiler brands. They offer the ideal combination of excellent customer reviews, warranty periods, technical brilliance, efficiency, and power.

Curious to know how condensing boilers differ from combi boilers? Read condensing boilers vs combi boilers

Best Condensing Boilers - Our Conclusion

Best Condensing Boilers: Conclusion  

The average boiler lasts around 10 years and performs the very important role of keeping your home heated and supplied with hot water.

Therefore, you want to buy a boiler that’s going to perform well with limited to no down time - and in the event that there are any issues, a warranty that will help you get it back to operation in next to no time. 

That is why the condensing boilers and brands that have been mentioned within this article have been selected based on the most important metrics: reliability, customer reviews, availability of parts, price range, and efficiency ratings.

Condensing Boiler Diagram

If you are wondering whether you should repair or replace your old boiler, it usually makes financial sense to get it replaced sooner rather than trying to keep it running.

Whatever your budget there is sure to be a condensing boiler suitable for you and your home, whether you want a premium boiler from the likes of Worcester Bosch or Viessmann, or a more budget-friendly option like the Alpha E-Tec. 

And remember whichever brand you choose - Worcester Bosch, Viessmann or Alpha, you will secure an exclusive 10 year warranty when you purchase your new boiler via Heatable, offering you long term peace of mind. 

Advantages of Condensing Boilers

Advantages of Condensing BOilers

Here are the main benefits of a condensing boiler

More Energy Efficient Boilers  

Modern condensing boilers are much more efficient than non-condensing boilers, this means that they produce more heat from the energy used and waste less energy during the process. 

ERP Rated Condensing Boiler For example, non-condensing boilers could be less than 60% efficient and were rated as G under the ERP (Energy Related Products Directive) boiler rating system. Condensing boilers on the other hand are at least 90% efficient and are A-rated boilers, the highest rating possible. 

Firstly, they can help you save energy (and money!) 

According to the Energy Saving Trust by replacing your old G-rated non-condensing boiler with a modern A-rated condensing boiler you could save as much as £300 a year.

Paired together with a smart thermostat and thermostatic radiator valves you could save even more. By installing a Nest, you could save up to £75 and 330kg of carbon a year, thanks to its adaptable learning schedule.

Plus, they reduce your carbon footprint 

Modern A-rated condensing boilers have a considerably lower carbon output than old non-condensing boilers. In fact, by trading your old boiler in for a modern condensing boiler you could save up to 1,220 kg of CO2 per year.

Frequently Asked Questions (FAQs) 

Condensing Boiler FAQs

What is a Condensing Boiler? 

BoilerPlus LogoDue to environmental concerns, in 2005 Boiler Plus legislation meant that all new boilers had to use condensing technology, resulting in boilers that are much more efficient than the previous non-condensing models. 

Essentially, a condensing boiler is able to use more of the heat that is produced and less is lost to the external environment. For example, in non-condensing boilers, a large amount of the heat produced is lost with the flue gases meaning more heat from the burner is required. 

How does a Condensing Boiler Work? 

Condensing boilers are able to recycle the heat from the flue gases, which can then be reused to preheat the cold water entering the boiler. 

During this recycling process, the temperature of the flue gas can quickly fall by as much as 80 ℃. This rapid drop can result in condensation hence the name condensing boiler. 

As a result, the latent heat in this vapour is no longer lost, resulting in heat that can be used and as much as two litres of wastewater per hour, which leaves the boiler via the condensate pipe. 

This means that condensing boilers are much more efficient since they are able to use heat that is already present, they can help save energy, resulting in lower heating bills and a lower carbon footprint. 

If you live in average size home, you may find our guide on choosing the best boiler for a 3 bedroom house helpful. 

Condensing Boilers Vs Non-Condensing Boilers

Condensing Boilers vs Non Condensing Boilers

Combi boilers and heat-only/regular boilers can be condensing or non-condensing, but the law and current building regulations state that all new installations in residential properties must be condensing. 

A non-condensing boiler works by taking air in from inside the room, while a condensing boiler will be completely sealed and takes in air directly from the outside.

What’s the difference between a condensing boiler and a combi boiler? 

A combi boiler or combination is a type of boiler able to supply both hot water and heating from a single unit. 

Rather than a type of boiler, condensing is more of a technical attribute related to the technology a boiler uses. For example, condensing boilers have a much larger heat exchanger and recycle heat from the waste flue gases, which would have been wasted in non-condensing boilers, making them much more efficient. 


Old, non-condensing boilers were as much as 50% less efficient, since a lot of the heat produced was lost via the combustion exhaust gases. However, new boilers are designed in such a way that this heat is captured and used to heat water too. 

All condensing boilers are at least 90% energy efficient, can harness excess energy to heat your home, are better for the environment and will help to reduce your heating bills.

Are Condensing Boilers Safer? 

Condensing Boilers Safety

Non-condensing boilers were designed to take in air from the room, resulting in a hazard of things being potentially sucked into the boiler. 

Condensing boilers on the other hand take in air directly from the outside of the room, so there is no such risk. 

In addition, since waste water is removed by a condensate wastewater pipe, there is reduced risk of coming into contact with any harmful vapours. 

What Size Condensing Boiler do you need? 

What Size Condensing BOiler

Here is a quick overview of the condensing boiler size you need:

Best condensing boilers for small homes:

  • #1 - Viessmann Vitodens 100-W 26kW
  • #2 - Baxi 600 – 24kW / 30kW

Best condensing boilers for large homes:

  • #1 - Viessmann Vitodens 100-W 35kW
  • #2 - Worcester CDi Classic 38kW

Best offensively large, powerful combi boilers:

  • #1 -  Worcester CDi Highflow 44kW / 55kW
  • #2 - Viessmann 111-W 35kW

Want to know the kW you need for your home? Check out our "what size boiler do I need" guide.

Condensing Boiler Costs

Condensing Boiler Costs

The cost of a new condensing boiler is dependent on a variety of different factors, these include the following:

One of the most common and straightforward types of condensing boiler installations is a straightforward combi swap i.e. replacing your old combi with a new combi. This is much simpler than replacing a combi with a system boiler.

This is due to conversions being more complex to install, taking more time, requiring more labour and more materials. More everything.

The condensing 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.

Looking for the best deal on a new boiler? 

If so, get your new condensing boiler installed with Heatable, here’s why: 

  • Gas Safe installation within 24 hours
  • Thousands of happy customers – an average score of 4.9 on Trustpilot (that’s better than the market leader).
  • Price match guarantee – if you find a cheaper quote, we will match (must be like for like)
  • Multiple payment options - interest free available
  • 10 year guarantee
  • Fixed price guarantee – no hidden costs
  • Save your quote until later

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Heatable is registered in England and Wales No. 08804726 (VAT No. GB205805920 ). Trading address is 1 Station Road, Great Sankey, Warrington, Cheshire, WA5 1RH. Heatable acts as a credit broker (not as a lender) and offers credit products through a panel of lenders. Heatable is authorised and regulated by the Financial Conduct Authority (reference no. 805259).

[1] Price based on a like for like combi swap in a 2 bed, 1 bathroom terraced home with a standard flue

[*] Installation dates are subject to installer availability

[ยน] only available on combi boiler installations

Financial Support: If you are in receipt of certain benefits, you may be entitled to claim a free boiler grant.