Best-selling combi boilers in 2023 (heating expert opinion) Re February 10, 2023

Best-selling combi boilers in 2023 (heating expert opinion)

Ferroli Fault Codes

Need a new boiler and don’t know where to start? Worry not – our heating whizzes are here to help!

We have gathered tons of data to give you a list of the best boilers money can buy. We based our recommendation on build quality, heating engineer preference, energy efficiency, heat output, brand aftercare and, most importantly, the boilers loved (and bought) by many WarmZilla customers. 

Now let’s dive into it – what are the best combi boilers on the market? And what makes them the best choice?

Best-selling combi boilers on the market

Worcester Bosch Greenstar 4000

WB 8000

Technical spec

Efficiency: A-Rated (94%)

Heating output: 25kW and 30kW

Size: Height 710mm – Width 400mm – Depth 310mm

Cost: From £2,219 (for a standard installation)


Whether you have a cute little small home or a mid-size home with one bathroom, this boiler is an excellent choice. The Worcester Bosch Greenstar 4000 is available as a combi boiler and system boiler with outputs between 12kW and 30kW. 

The Greenstar 4000 Combi is known for its sleek, minimalistic design and looks beautiful on any wall. The boiler’s full-colour text display is easy to read.

The Greenstar 4000 is so quiet you could hear a pin drop (unless you have kids!)

Save money with the Greenstar 4000 Combi

The Worcester Bosch Greenstar 4000 is an incredibly efficient A-rated boiler with a 94% efficiency – meaning for every pound spent heating your home, only 6p gets wasted in the atmosphere. 

According to the Energy Saving Trust, you could save up to £840 a year by upgrading your old inefficient boiler to an A-rated boiler, which typically operates at 90% and over energy efficiency. Note – Figures are based on fuel prices as of October 2022. 

The boiler’s innovative ‘Quick Tap’ water-saving function also helps you reduce water waste. 

Like a Bosch

Based on the design of the famous, best-selling boiler on the market, the Worcester Bosch Greenstar i, Worcester Bosch have created a new and improved version, raising the bar with ease and speed of installation, commissioning, and servicing. The exterior of the 4000 series is very similar to that of the Worcester Bosch 8000 Life and Style boiler range, but it is significantly cheaper. This means you get all the great features and benefits of the Worcester Bosch Greenstar i for less. 

The Worcester Bosch 4000 is available as a combi boiler with outputs of 25kW and 30kW and a flow rate of up to 12.3 l/min. The 4000 system boiler, on the other hand, is available in 12kW, 15kW, 18kW, 21kW, and 24kW.

Greenstar 4000 stunning design

The boiler’s attractive exterior looks great and blends with all homes’ aesthetics. The curved-edge boiler shape and smart display bring a modern touch to your home rather than the traditional square white box on a wall.

Control your boiler from your smartphone with the Bosch EasyControl

If you’re on your way home from a freezing cold office and want to turn up the heat, you can do that on the go using only your smartphone.

With the smart wireless connectivity feature, you can connect your boiler to the Bosch EasyControl and control your home heating from any smart device.

Greenstar 4000 - a hydrogen blend boiler

We’re now getting closer to Net Zero targets, and the UK is under pressure to find sustainable solutions to our everyday life activities – including the way we heat our home; hence hydrogen heating is a priority.

Worcester Bosch’s entire gas boiler range can run on a 20% hydrogen blend – so you can be confident that this boiler is future-proof; meaning it can use hydrogen as a fuel source if needed, but it also can run on gas for the time being until the switch.

Worcester Bosch Greenstar 4000 guarantee

A boiler guarantee is nearly identical to a boiler warranty. It’ll always come with one as standard, varies in length, and can be extended for an additional cost. There is only one difference between the two, and that is that a boiler manufacturer’s guarantee is a promise to repair your boiler for a certain amount of time after installation, no matter what the cause. There is no small print that can catch you out if certain things may have caused the boiler to break down. The manufacturer will send an engineer to your home and repair it regardless. 

Worcester Bosch is one of the few manufacturers to offer a guarantee rather than a warranty. This is a major selling point and could often be the deciding factor in choosing your new boiler. Enjoy a 10-year guarantee when you buy a Worcester Bosch Greenstar 4000 for additional peace of mind.

About Worcester Bosch

Worcester Bosch is a leading manufacturer of high-quality boilers. 

When it comes to heating and hot water solutions, Worcester Bosch is a well-known and respected brand in the UK and around the world. With over 50 years of experience in the industry, Worcester Bosch has established itself as a leader in the design, manufacturing, and distribution of high-quality boilers and controls. Whether you’re a homeowner or a landlord, Worcester Bosch has a solution to meet your needs. 

At the heart of Worcester Bosch’s success is its commitment to innovation, quality, and customer satisfaction. The company invests heavily in research and development to ensure its products are at the forefront of the latest advancements in heating technology. This dedication to innovation has resulted in a range of boilers that are not only efficient and reliable but also easy to install, operate, and maintain. 

Worcester Bosch offers a wide variety of boilers to suit every need, from compact combi boilers for small homes to larger system boilers for larger properties. Whether you’re looking for a high-efficiency model to save on energy bills or a condensing boiler for enhanced performance, Worcester Bosch has you covered. 

In addition to its boilers, Worcester Bosch also offers a range of controls and accessories, including thermostats, programmers, and zone valves. These controls are designed to work seamlessly with Worcester Bosch boilers, providing optimal heating performance and comfort. They are also easy to use and feature intuitive displays and user-friendly interfaces. 

Worcester Bosch is proud to offer excellent customer service and technical support to its customers. The company’s knowledgeable and experienced team is always on hand to answer any questions or provide assistance with installation and maintenance.

In conclusion, Worcester Bosch is a trusted and reliable choice for anyone in need of a high-quality boiler. With its commitment to innovation, quality, and customer satisfaction, Worcester Bosch is a brand you can trust to provide a solution that meets your needs and exceeds your expectations.

Worcester Bosch aftercare

Straight off the bat, Worcester Bosch is not only known for providing thousands of households with reliable and efficient central heating systems, but they also provide the best aftercare there is, and here’s why.

Worcester Bosch prides itself on its superb customer aftercare. It is something that you can clearly see throughout their excellent Trustpilot reviews, and that’s what earned them their 4.6 stars. If you’re not sold yet, read what their customers said about them:

“My choice of boiler was influenced by personal experience of Worcester Bosch. I have visited the factory, seen their impressive training facilities and production line. This is a good quality brand, made for decades in Britain. The 10 year guarantee backs up this reputation and was also important in my choice. The boiler has now been installed for 12 months.”

Another customer said:  

“Our old boiler of nearly 20 years a Worcester was due for replacement. This boiler had given us great service during that period with very few problems..It was a no brainer to replace it with another Worcester and we opted for the green star far so good definitely hotter and without a doubt more energy efficient by far than the old boiler.”

When you take a look at the Which? Independent review for the Worcester Bosch 4000

Overall score



Brand reliability rating

4 stars

Brand customer score rating

5 stars

Ease of fixing a common fault

5 stars

Ease of servicing 

5 stars

Availability of parts and spares

5 stars

Engineer recommendation

5 stars

Build quality 

5 stars

Worcester Bosch Which? Verdict

Reliable and well liked by owners for more than a decade

Worcester Bosch is our top gas boiler brand, because its boilers have a long life and it has the happiest customers. Expert engineers are positive about Worcester Bosch, too, especially when it comes to the ease of sourcing spare parts (though some repairs are reportedly fiddly). Worcester Bosch has been a Best Buy gas boiler brand for more than a decade, and with such a high proportion of its customers recommending the brand, it continues to be recommended by us.

Ideal Logic C30 Combi Boiler


Technical spec

Efficiency: 89%

Heating output: 30kW

Size: Height 700mm – Width 390mm – Depth 270mm

Cost: From £1,945 (for a standard installation). 

The Ideal Logic C30 Combi Boiler is a high-efficiency boiler suitable for smaller homes and apartments. With a compact design, it can be easily installed in a cupboard or utility room. The C30 features a 30kW output, making it suitable for properties with 1-2 bathrooms. It utilises advanced technology to provide quick and efficient heating, and also has a modulating burner for precise temperature control. Additionally, the C30 is equipped with a user-friendly digital display and a variety of safety features for added peace of mind.

The Ideal Logic C30 design

The Ideal Logic C30 Combi Boiler has a compact and stylish design, making it a great choice for smaller homes and apartments. Its compact size allows for easy installation in a cupboard or utility room, freeing up valuable living space. The C30 has a sleek and modern look, with a clean white finish and a user-friendly digital display.

The C30 features a modulating burner that adjusts the heat output in response to demand, ensuring precise temperature control and improved efficiency. The boiler also has a range of safety features, including a pressure relief valve and an automatic bypass, to provide added peace of mind.

In terms of ease of use, the C30 is equipped with a user-friendly digital display that provides real-time information on the heating and hot water performance. The display also features an intuitive interface and a variety of diagnostic tools to help diagnose any issues that may arise.

Overall, the Ideal Logic C30 Combi Boiler has a modern and functional design that combines style with performance and safety. Its compact size, energy efficiency, and user-friendly features make it a popular choice for homeowners.

Ideal boiler reviews

Which? Best Boiler Brand Survey Results for Ideal Boilers

Overall score


Brand reliability rating

5 stars

Brand customer score rating

4 stars

Ease of fixing a common fault

4 stars

Ease of servicing 

4 stars

Availability of parts and spares

4 stars

Engineer recommendation

3 stars

Build quality 

3 stars

Their customer score was 4 out of 5 stars. Which? describes Ideal as having “a good reliability record, a good customer score, and our expert heating engineers rank it above average too”. 

Ideal has this to say of themselves on their website:

“Today, Ideal remains at the forefront of the domestic and commercial heating markets, leading the industry in setting new standards and challenging technological boundaries. Our company remains true to its founding principles of quality, innovation, and value – building on its rich heritage as we look to the future.” 

Now we know more about the background and success of Ideal Heating as a boiler brand, let’s get into why the Ideal Logic boiler range, predominantly, the Ideal Logic C30, is one of the best-selling combi boilers on the market.

The Ideal Logic Combi Gas Boiler comes in 3 different output options. Despite them all having the same kW output of 24.2kW for central heating (CH), these boilers differ in their domestic hot water output (DHW), with the C24 offering 24kW output, the C30 offering 30kW, and the C35 offering 35kW. Each model also offers progressively higher flow rates.

The Ideal Logic C30 combi boiler warranty

The Logic range only comes with a 2-year standard manufacturer’s warranty, which is significantly less than other Ideal boiler models, such as the Ideal Vogue and the Ideal Max. However, if you purchase through us here at WarmZilla, all Ideal boilers come with 8 years guarantee. 

It is important to note that unless the warranty is registered within 30 days of installation, it becomes void but don’t worry about that because we’ll register the warranty on your behalf. You must also have your boiler services annually for your warranty to be in use. As a WarmZilla customer, you can buy an exclusive boiler service package to ensure you never miss a service.

About Ideal Heating

Ideal Heating is the UK’s leading boiler manufacturer. The company has been in business for over 100 years and is known for manufacturing high-quality boilers, including combi boilers, system boilers, and heat-only boilers. Ideal Heating is committed to providing energy-efficient and environmentally-friendly products to its customers. In addition to boilers, the company also offers a range of controls, including thermostats and programmers, to help optimise heating and hot water performance. Ideal Heating is dedicated to providing excellent customer service and technical support, making it a trusted and reliable choice for your home.

Ideal Heating aftercare

Ideal also has a great aftercare service for its customers.

Ideal’s Customer Service team is available 7 days a week, 364 days a year. Ideal also offers a live chat option on their website so that any issues you may have can be resolved promptly.

Ideal’s website has a good range of support you can access yourself, such as a tips & advice tab, an FAQ section, and help videos, to ensure maximum comfort in your home.

Viessmann Vitodens 050-W 30kW Combi Boiler

Viessmann 050

Technical spec

Efficiency: A-rated (97%)

Heating output: 25kW, 30kW, 35kW

Size: Height 700mm – Width 400mm – Depth 300mm

Cost: From £2,225 (for a standard installation).


The Viessmann Vitodens 050-W Combi is a highly efficient and reliable boiler. This compact and stylish boiler provides both heating and hot water on demand, eliminating the need for a separate hot water storage tank.

One of the standout features of the Vitodens 050-W is its high energy efficiency rating. The boiler is rated at 94% efficiency, meaning that it can help to reduce your energy bills and carbon footprint. It also features a modulating burner that adjusts the heat output in response to demand, ensuring precise temperature control and improved efficiency.

Viessmann Vitodens 050-W 30kW combi boiler design

The Vitodens 050-W has a sleek and modern look, with a clean white finish and a user-friendly digital display. It is designed for easy installation, with a compact size that allows for flexible placement in many locations. The boiler also features a range of safety features, including a pressure relief valve and an automatic bypass, to provide added peace of mind.

In terms of ease of use, the Vitodens 050-W is equipped with a user-friendly digital display that provides real-time information on heating and hot water performance. The display also features an intuitive interface and a variety of diagnostic tools to help diagnose any issues that may arise.

Overall, the Viessmann Vitodens 050-W Combi Boiler is a high-performing and reliable heating solution that is well-suited for smaller homes and apartments. Its energy efficiency, compact size, and user-friendly features make it a popular choice. 

Another reason to get a Viessmann boiler is its one-of-a-kind stainless steel heat exchanger. There are many benefits of using stainless steel for the heat exchanger. First, stainless steel offers impressive resistance against corrosion, meaning your heat exchanger is more likely to last for longer and maintain its efficiency, saving you money on your heating bills. Second, stainless steel heat exchangers can withstand a higher flow rate than exchangers made from other materials. If more gas or water can pass through faster, water can be heated up more quickly. This increased flow rate also minimises the risk of blockages within the exchanger from debris or rust, which could increase its lifespan. Finally, stainless steel is self-cleaning and a very lightweight material, making it ideal for various appliances that require water to be heated. 

All Viessmann’s condensing boilers have stainless steel heat exchangers, so you can be assured that your boiler will run at maximum efficiency.

Viessmann Vitodens 050-W 30kW combi boiler warranty

The Viessmann Vitodens 050-W 30kW Combi Boiler comes with a comprehensive 10-year warranty to provide peace of mind and protect against potential issues.

Viessmann - German engineering at its finest

Viessmann is a German manufacturer of heating and cooling systems, including boilers, solar thermal systems, and geothermal systems. Founded in 1917, Viessmann is one of the largest and most well-established heating equipment manufacturers in the world, with a reputation for high-quality products and innovative technology.

Viessmann offers a wide range of boilers for residential and commercial use, including combi boilers, system boilers, and conventional boilers. These boilers are known for their high energy efficiency, reliable performance, and advanced features, such as modulating burners and user-friendly controls.

Viessmann is committed to sustainability and environmental responsibility, with a focus on reducing energy consumption and carbon emissions through its products and manufacturing processes. The company has received numerous awards and accolades for its commitment to sustainability and is widely regarded as a leader in the heating and cooling industry.

In conclusion, Viessmann is a well-respected and innovative brand in the heating and cooling industry, known for its high-quality products, energy efficiency, and commitment to sustainability. Whether you are looking for a reliable and efficient boiler or a renewable energy solution, Viessmann has a range of products to meet your needs.

Viessmann aftercare

Viessmann is also known for its world-class service and aftercare. Their customer service team is here to support you throughout your boiler’s lifespan.

Viessmann reviews

We understand how important it is to ensure that you are 100% happy with your choice of boiler before investing in it, as a boiler is not cheap and will need to last you at least 10 years (if maintained properly).

When looking at Viessmann’s Trustpilot ratings, we can instantly see that customers love their boilers and are more than satisfied. This is supported by an average rating of 4 out of 5 and over 4k reviews. For this reason, let’s look at what Viessmann’s customers say about their Viessmann boiler. 

“Had it fitted by a super-knowledgable engineer last September and was sceptical that leaving it on simmering all the time would not cost more than my old boiler which we only turned on twice a day for an hour or two. This winter, I haven’t noticed the difference in outside temperature when in the house – always a constant warmth – and my bills are the same, if not less than previously! I love that I can control everything via the app and that my engineer gets alerts so can step in on the app rather than having to visit (not that he’s had to). Good money spent!”

And another customer said:

“Our new boiler was a replacement of Veissmann boiler, which in itself is a testament to the quality of product and service we had come to expect. The new model is a stylish, efficient and easily operated boiler.”

In 2022 Which? Best Boiler Brand Survey where over 8,000 customers and 150 Which? Trusted Traders were asked to score Viessmann on their reliability, how likely they are to recommend their Viessmann boilers to friends and family, the build quality of their Viessmann boiler, the ease of servicing and availability of spares and parts. 

Viessmann scored an overall 81% brand score. Customers and tradesmen scored an amazing 5 out of 5 stars for reliability and customer score and 4 out of 5 stars for their overall engineer recommendation score, which supports the fact that Viessmann is a highly reliable and efficient boiler brand.

Which? Best Boiler brand 2021 survey results for Viessmann boilers

Overall Score 



4 stars

Customer Score 

5 stars 

Engineer Recommendation

4 stars 

Build Quality 

4 stars

Availability of Spares and Parts 

3 stars

Ease of Fixing a Common Fault

4 stars 

Ease of Servicing 

4 stars

Combi boilers: The verdict

You can’t go wrong with any one of these boiler brands (Worcester Bosch, Ideal and Viessmann). If you’re looking for a boiler with the longest guarantee, we recommend going for Worcester Bosch Greenstar 4000.

If budget is a determining factor, then Ideal Logic C30 Combi Boiler will be the ‘ideal’ choice for your home, no pun intended!

And if you’re aiming to get a robust boiler with excellent engineering, great aftercare and reasonably priced, then add the Viessmann Vitodens 050-W 30kW combi boiler to your basket.

Still not sure which boiler to get? Contact us and we’ll help you find the boiler that suits your home. Our team is knowledgeable, experienced and loves to help. Our customers love us! Check out our excellent rating on Trustpilot.

Get your boiler with WarmZilla now

When you buy a new or replacement boiler with WarmZilla, your boiler package will include;

  • Your chosen boiler, along with the necessary flue kit needed for your central heating system
  • Installation by a qualified Gas Safe Engineer 
  • Removal of your old boiler and parts
  • A FREE system cleanse of your central heating system
  • Chemical Inhibitor for added protection for your new boiler
  • 10-year guarantee, which will be registered by WarmZilla after installation
  • A FREE magnetic system filter for ongoing protection
  • The Neomitis RF Digital Wireless Room Thermostat
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