Guide to the Best Combi Boilers

Installing a new boiler is a major investment, but an investment that could see you save many hundreds of pounds over its lifetime.

But how do you decide which model to choose?

We’ve produced this handy guide to get you familiarised with the big and reliable brands out there on the UK market. But first a little bit of background info on condensing boiler types.

Combi Boilers vs System Boilers

Regulations in the UK now mean that all boilers have to be condensing types. This means they recover the heat which would, in other designs, be vented and thus wasted via the flue. This can save you around a third on your fuel bills.

The most popular type of condensing boiler is the combi boiler (short for combination boiler). These supply heat to your radiators in the normal way, but instead of heating water and storing it in a cylinder for later use, they heat it on demand when you turn on the tap. The advantage of this is that you don’t need a cylinder or a cold water header tank in the loft, so you save space. The boilers are also usually compact enough to fit in a kitchen cupboard. The downside is you may have to run the tap for longer before the water starts to get hot.

Combis are less suitable for large houses or large families where you may need to access hot water in two places at once. So if you have a regular bathroom and an en-suite, for example, a combi may not be the best choice. In this case, you need a conventional or system boiler; this will still be a condensing type but will have a cylinder to store hot water and usually a header tank too. Also once you’ve used all of the hot water in the cylinder you’ll have to fire up the boiler to create some more.

Before deciding on what type of boiler to choose, you need to consider the size of your property and family and look at how you use hot water through the day. Combi boilers come in different outputs, a small house or flat with up to 10 radiators and a single bathroom will need a 24 – 27kW boiler. Larger properties with up to 15 radiators and one or two bathrooms should have a 28 – 34kW model. A large house with up to 20 radiators and two or more bathrooms will need a 35 – 42kW output boiler.

The Big Combi Boiler Brands in the UK

So, having considered all of this and deciding that a combi is the right choice for you, what are the big and trusted brands in the UK market that you should be looking at? Read on because we’ve listed them all here for you…

Worcester Bosch is one of the best-known names in the boiler market. Their boilers are a popular choice and the widely used Greenstar i model is available in different outputs so it’s suited to different sizes of property.

Worcester has won the Which? best buy award several years running and has a strong reputation for reliability and performance. The company produces a range of boilers including oil and LPG types. They have simple controls and are compatible with solar water heating systems, so are a good choice if you are going green. Worcester Bosch boilers are not the cheapest, but their reputation and long warranty make them a strong contender for your hard-earned cash.

Best Worcester Bosch Model: Worcester Greenstar 30CDi Classic

If you’re looking for a quality boiler for a property with one or two bathrooms, the Worcester Greenstar 30CDi Classic boiler is a highly-efficient boiler with advanced features and easy installation.

Being a SEDBUK A rated boiler, the Worcester Greenstar 30CDi Classic is highly recommended for new installations. Some of the key features of this quality Worcester boiler include A rated efficiency, EasyControl Compatible, no exposed pipework, low NOx and CO2 emissions.


Vaillant is another well-known brand. The company manufactures its boilers in the UK and has been making heating systems since the 1870s. The latest models incorporate German engineering and there are a number of options available, suitable for different types of home.

The Vaillant ecoTEC Plus is a model designed for larger properties and offers rapid hot water delivery, in five seconds or so. Vaillant models are covered by a five-year warranty as standard, but if installed by a Vaillant approved installer this can be extended to seven or 10 years.

Best Vaillant Model: EcoTEC Exclusive with Green IQ

Another highly efficient and quality model of boiler is the EcoTech Exclusive with Green IQ. This combination boiler is best suited to properties with two to four people and with up to two bathrooms.
The cost-effective Vaillant EcoTech Exclusive with Green IQ is designed to lower energy consumption and therefore energy costs in a home as it is able to modulate its output to just 10% of the total output provided. With a 43W output, this combi boiler provides premium hot water performance, turning an incredible 17.8 litres of water hot every minute.


Ideal is another established manufacturer and has been making boilers in the UK for more than 100 years. Ideal’s Logic+ range is endorsed by the Energy Saving Trust and has won numerous awards. The boiler has a seven-year warranty but the heat exchanger – the heart of the boiler – is warranted for 10 years.
The Logic+ is available for mains gas and for LPG. Ideal boilers offer better value for money than some other well-known makes and so is a popular choice with both householders and installers. System boilers as well as combis are available.

Best Ideal Model: Ideal Independent C24

If you are looking to have a new boiler installed in a smaller property like an apartment or small house, the Ideal Independent C24 comes highly recommended.

This practical and economical combi boiler provides A rated performance, a DHW output of 24W and a central heating output of 24kW. As well as being highly efficient and great value, other key advantages of the Ideal Independent C24 is the fact it’s quick and easy to install, provides frost protection, has a built-in mechanical timer and is extremely compact, making it perfect for smaller homes that are sparse of space.


Baxi is another well-known brand in the UK and its boilers have high levels of customer satisfaction and come with a 10 year warranty. The company is perhaps best known for back boilers, but it makes combis and system types too.

Baxi’s Eco Blue range is available with outputs from 24kW up to 40kW. They are A-rated for efficiency – as all good combi boilers should be – and offer fast delivery of hot water and have user-friendly controls.

Best Baxi Model: Baxi EcoBlue Advance 33 Combi

For older properties, which have relied on the same hot water and heating systems for many years, updating the boiler with a Baxi EcoBlue Advance 33 Combi Boiler would be a wise choice.
This wall-mounted boiler has an A rating for efficiency. Being extremely compact and lightweight, weighing just 20kg, the Baxi EcoBlue Advance 33 Combi Boiler is easy to install and is suitable for smaller properties that have limited space.


Glow-Worm has been manufacturing boilers in its Derbyshire factory for more than 80 years. Its boilers come with a seven-year guarantee and it offers a range of high-efficiency models suitable for both large and small properties. LPG models are available too.

If you are on a tight budget, Glow-Worm also produces a range of value for money combi boilers. The Betacom, for example, is still an A-rated boiler, available in 24kW or 30kW outputs, but comes only with a two-year warranty – with the option to extend. If you are able to spend a little more, the Easicom is warranted for four years.

If you own a larger property and you’re looking for an efficient and cost-effective way to heat your home, the Glow-Worm 35kW Combi Boiler comes highly recommended.

This Glow-Worm boiler is ErP A rated for high efficiency, helping you reduce costly energy bills in a large home. The combi boiler provides instant and unlimited hot water and is LPG compatible, making it the perfect option to give large properties instant hot water and maximum comfort.


Viessman is a name that you may not have heard of, but it has a growing reputation. Its Vitodens boiler range is Which? recommended and quiet in operation. It has touchscreen controls and a warranty of seven years extendable up to 10 years. It’s also one of the most compact boilers in its class, so if space is at a premium in your home, the Viessman range is worth a look.

Best Viessman Boiler: Viessmann Vitodens 050-W

For small homes wanting to have an efficient boiler installed, the super-compact and low-cost gas condensing boiler the Viessmann Vitodens 050-W, would make a great choice of new boiler.

As well as being compact and lightweight, the Viessmann Vitodens 050-W is extremely quiet, ensuring it integrates seamlessly into contemporary living spaces, even those that are sparse of space. The DHW output ratings of the Viessmann Vitodens 050-W is 5.9 to 35kW. The boiler also produces integral instantaneous hot water.

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