10 July, 2020

Top 5 Best Combi Boilers 2021

Find out our 5 favourite combi boilers on the market in 2021.

Top 5 Best Combi Boilers 2021

Are you looking to replace your combi boiler this year but don’t know which boiler to go for? Then you’ve come to the right place!

This guide will give you the Top 5 Best Combi Boilers of 2021 and help you to evaluate which is right for you! But first, let’s start out with what a combi boiler actually is.

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Whats in this article?

What is a combi boiler?

A combi or combination boiler combines a water heating system and central heating unit into a single body, acting as a unified way to handle heating and hot water without needing two separate boilers.

This means there is no need for a separate water tank system and therefore takes up less space in your home. A combi boiler is one of the most efficient types of boilers to install and tends to be much more reliable than normal boilers which is why we love them so much!

Find out more about combi boilers here.

Why should I buy a new boiler?

According to the Energy Saving Trust, if your combi boiler is over fifteen years old and is a non-condensing boiler, it will be less efficient and may become faulty and even break down on a regular basis, as a result of corrosion on internal components from the thermal and mechanical stresses over years of constant use.

Not only is this an inconvenience for you, but it could also be costing you a lot more money to run an old inefficient boiler that frequently requires costly repairs, than it would to run a new A-Class efficiency rated combi boiler.

According to The Energy Saving Trust, you could start saving up to £340 annually on your energy bills by replacing your boiler.

You can also have a read up on new boiler costs.

Which boiler should I buy?

There are so many combi boiler brands and models to choose from, that deciding on which combi boiler is best for you, might seem impossible.

Boilers are also available at many different price points, which is another factor to consider when preparing to make a purchase.

That’s why we have researched and read plenty of reviews to compile our Top 5 Best Combi Boilers of 2021, with reasons why we love them so much. Keep reading to find out our favourite!

Best Combi Boiler by Alpha Innovation Company

#5 Alpha Combi Boilers

In fifth place comes Alpha, a well-established brand that has been one of the UK’s leading heating companies for over 50 years, giving them plenty of experience that combines traditional business values with a highly innovative approach to its operation.

Alpha ranks among the best because they have amazing A-Class efficiency rated budget boilers that accommodate the needs of every property type and household size. As part of the Immergas group which operates in 30 countries and has manufactured over 7 million boilers, Alpha benefits from some of the most advanced production facilities in the world.

This means you are guaranteed a high quality boiler, despite the low prices. They offer a range of boiler sizes from the compact E-Tec to the larger E-Tec Plus which deliver on every aspect.

Alpha Boiler Range

Alpha Model Kilowatt (kW) Outputs
E-Tec 28 33 -
E-Tec Plus 28 33 38
Evoke 28 33 -
InTec 28 33 -


The E-Tec is ideal for small and medium sized homes. The entire E-Tec range features brand new stainless steel heat exchangers, making them highly robust and they also have zinc plated expansion vessels to prevent corrosion.

Taking these extra steps to maximise the longevity of your boiler life is what makes this range stand out. The E-Tec also has a high-efficiency pump which helps to deliver an impressive 14.1 litres of hot water per minute and the single electrode drive charge is very easy to access, meaning your Alpha boiler will be easy to control and manage after installation.

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Just some of the features of the E-Tec include:

  • 7 Year Warranty
  • Two available kW outputs
  • Combined condensate and pressure relief valve connection
  • Single Electrode
  • Easy-access dry-change NTCs on front of pipes

E-Tec Plus

The E-Tec Plus is similar to the E-Tec but is much larger and has a few extra benefits, such as a 10 year warranty, copper pipe tails with isolation valves, an integrated filling loop and a control panel and bottom cover. This combi boiler is suitable for larger homes and offers a third higher output option than the E-Tec at 38kW


The best boilers from Alpha are the smallest. Its compact size and layout is an ideal solution for small to medium sized homes and has a stainless steel heat exchanger and many other amazing features such as:

  • 7 Year Warranty
  • Backlit LCD with push button controls and detailed operational information
  • High efficiency Grundfos pump and hydroblock assembly
  • Single electrode
  • Easy access for servicing
  • IPX4D protection
  • Low electrical consumption
  • Easy-access NTCs on front of pipes
  • One-piece cartridge diverter valve
  • Clip-on DHW temperature sensor
  • Dry-change NTCs
  • Combined condensate and pressure relief valve connection
  • Frost protection and daily pump kick
  • 14.1 litres of water per minute


The InTec combination boiler is different from the others due to its built-in GasSaver.

This boiler is perfect for anyone who is concerned about their impact on the environment as the InTec reduces gas usage by 35% compared to other gas boilers and has a low electrical consumption.

Some of the useful features of the InTec are:

  • Same connections as a boiler with no additional exposed pipework
  • Isothermic stainless steel heat exchanger
  • High efficiency Grundfos pump and Hydroblock assembly
  • Backlit LCD with push button controls
  • Two available outputs
  • Easy-access NTCs on front of pipes
  • One-piece cartridge diverter valve
  • Clip-on DHW temperature sensor to prevent corrosion
Some of The Best Combi Boilers by Ideal

#4 Ideal Combi Boilers

In fourth place comes Ideal. This boiler brand is the best at small and affordable boilers such as the Logic range as well as flashier pricier models such as the Vogue range, catering for all their customers and their budgets.

Ideal Boiler Range

Ideal Model Kilowatt (kW) Outputs
Logic 24 30 35
Vogue Gen2 26 32 40
Vogue Max 26 32 40


Although the Logic boilers aren't as flashy as the rest of Ideal’s range, they’re reliable, compact in size and easy to use, earning The Queens Award in 2013 as well as The Good Housekeeping Award in 2013 and 2017.

Ideal offers a standard 2 year warranty which can be extended to 5 years, though with only a 3% chance of The Logic's best combi boiler breaking down, it looks like you won’t even be needing it.

Here are some of the features of the Logic boiler:

  • Large digital display
  • Easy to reach pressure gauge on front panel
  • Compact
  • Scratch resistant

Vogue Gen2

This is Ideal’s best combi boiler for its features and attractive design, whilst remaining compact. It has a backlit 3.5” LCD full colour display and has multi-function buttons for ease of use, built using premium components. Endorsed by the Energy Saving Trust, you can be sure that this boiler is better for the environment. This boiler comes with a standard 8 year warranty.

Vogue Max

Ideal’s newest premium boiler has the same fantastic features and attractive appearance of the Vogue Gen2 with the addition of a high quality Ideal System Filter which boosts the warranty from 8 to 10 years.

Some of the other features include:

  • Easy to read pressure gauge
  • Premium components
  • Full text support for fault modes
  • Stylish composite design with damped opening control cover and large rotary control dials
  • Service timer with telephone number/service display
A great range of Best Combi Boiler by Vaillant

#3 Vaillant Combi Boilers

In third place is Vaillant, another Which? Best Buy Award winner. Vaillant is a premium contender and offers a 5 star boiler range for both small and large properties, though they do have premium prices which aren’t too friendly to your bank account.

However, they do come with a convenient app to control your heating anytime, anywhere and have a 5 year warranty which can be upgraded to 7 or 10 years.

Vaillant Boiler Range

Ideal Model Kilowatt (kW) Outputs
ecoTEC exclusive - - 35 43
ecoTEC plus 25 32 35 38
ecoTEC plus store - - -- 38
ecoTEC pro 24 28 30 -
ecoFIT pure - 25 30 35

ecoTEC exclusive

This boiler is great for larger homes with its higher outputs. It has the potential to generate an impressive 17.8 litres of hot water per minute and is eco-friendly and 85% recyclable. Like all of the Vaillant products, the ecoTEC exclusive has been Quiet Mark approved, meaning it is one of the quietest products on the market.

ecoTEC plus

This is the all rounder of Vaillant’s combi boilers with the broadest range of kW outputs. It has precision heating to reduce fuel bills, delivers hot water within 5 seconds and has a 5 year standard warranty.

ecoTEC plus store

This boiler is a powerful solution for larger homes with its high performance control, efficiency and an integrated hot water storage device at the back of the boiler. Providing up to 20 litres of hot water per minute and hot water within 5 seconds, this boiler is appealing to large families with a high demand for hot water and comes with a 5 year warranty.

Vaillant ecoFIT pure

The ecoFIT pure is another of Valliant’s highly efficient, smart control and high performance boilers but much more compact to fit in a kitchen cupboard in a smaller home. This boiler comes with a less impressive 2 year warranty, but there is the option to increase this to 7 or 10 years for an extra cost.

UK born and bred company Worcester provides some of the Best Combi Boiler

#2 Worcester Bosch Combi Boilers

In second place come the Worcester Bosch boilers, the pioneers of combi boilers. In 2019, they secured a Which? Best Buy award for the 10th year and their bestseller, the Greenstar i can be found in over a million UK homes.

Worcester Bosch Boiler Range

Worcester Model Kilowatt (kW) Outputs
Greenstar i - - 25 30
Greenstar Si Compact - - 25 30
CDi Classic 29 34 38 42
CDi Compact - 28 32 36
CDi Highflow - - 44 55

Greenstar i

The Greenstar i is Worcester Bosch’s most popular boiler that is ideal for small to medium sized homes and has simple and easy to use controls. Here are some features of the Greenstar i:

  • Condensate discharge resilient to freezing up to -15?
  • Wide choice of controls
  • Low energy pump reduces electrical usage
  • Hot water instantly heated from cold mains
  • Achieves A-Rated efficiency
  • Fills a kitchen sink in 45 seconds

Greenstar Si Compact

This boiler has pretty much all the same features as the Greenstar i but is much more compact to enable it to fit in a kitchen cupboard. It also has extra features such as frost protection and can also fill a kitchen sink in 45 seconds.

CDi Classic

This is one of the more expensive boilers available, but does guarantee reliability, fuel efficiency and a user-friendly interface. Available in four heating outputs, this boiler is suitable for many property types and sizes. Its modulating pump and intelligent controls also allow a 30% electrical energy reduction. It also comes with a 5 year warranty for peace of mind.

CDi Compact

This boiler is like the classic except much smaller to enable it to fit in a kitchen cupboard, making it more ideal for smaller homes. It comes with frost protection, a user-friendly display and simple boiler controls to ensure you can manage your comfort and costs.

CDi Highflow

This boiler is an incredibly useful floor standing boiler for large homes with lots of bathrooms. It provides high hot water flow rates over 90 litres draw-off. It has a wide choice of simple to use controls and a temperature display, however, with having such a large unit, a large space such as underneath a kitchen counter is required.

In top place, Best Combi Boiler by Viessmann

#1 Viessmann Combi Boilers

In first place comes Viessmann. Viessmann surpasses all other best combi boiler brands in the market with their advanced German engineering and efficient heating systems that are a great value for money. This isn't to say we don't think the other boilers listed in this article are not some of the best combi boilers on the market, the Viessmann is just the cream of the crop!

Their prices are currently so low as they are still attempting to increase their exposure in Britain, so now really is the time to buy yours before the prices rise! Get your fixed quote here.

Viessmann Boiler Range

Viessmann Model Kilowatt (kW) Outputs
Vitodens 050-W - 29 35
Vitodens 100-W 26 30 35
Vitodens 200-W - - 35
Vitodens 111-W 26 - 35
CDi Highflow - - 44 55

Vitodens 050-W

The Vitodens 050-W 29kW in particular is the most reliable and has the highest quality with its stainless steel heat exchanger (which makes it extra robust), exceptionally quiet operation and an impressive water flow rate of 12 litres/min.

With compact dimensions and low weight, the Vitodens 050-W will integrate into any home without compromising on quality. Winner of the 2019 Which? Best Buy award, this boiler is Class-A rated for its energy efficiency and is easy to control with an LCD display.

Here are just some of the amazing featured this boiler has to offer:

  • 10 Year Warranty when installed with iHeat
  • Integral instantaneous water heater
  • High efficiency of up to 97%
  • Low CO2 emissions for reduced environmental impact
  • Digital user interface

Vitodens 100-W

This combi boiler has all the great features of the 050-W as well as extra features such as the extra 26kW output option and the user friendly backlit LCD Touchscreen for easy operation. This boiler was endorsed by Which? and up to 94% of the fuel used is converted into heat, making it more environmentally friendly and Boiler Plus ready.

Vitodens 200-W

If you’re looking for a boiler for a larger home, this is the boiler for you. It has greater efficiency and lower emissions, with up to 98% of the fuel used converted into heat. Despite having to operate on a larger scale, this boiler remains compact and quiet thanks to its low speed fan.

Viessmann have made this boiler incredibly easy to operate by incorporating a 7” colour touchscreen with an integrated WiFi interface for internet connection. It also has a new environmentally responsible MatriX-Plus burner which automatically adapts to the properties of different gas types to keep costs down and reduce the environmental impact of the boiler.

With its 10-Year Warranty you can be sure you’ll have a long lasting and reliable boiler.

Vitodens 111-W

Viessmann describes its Vitodens 111-W as rapid, reliable and compact- and that it is. This combi boiler is perfect for large families who have a high demand for hot water. With this high performance wall mounted storage boiler, you can be sure there will be no more arguments in the morning about ‘who is using all the hot water?!’.

With the capacity to fill a bath in just 8 minutes, this combi boiler will never fail to provide the means for a relaxing soak. Here are some of the features that are bound to impress even those with minimal boiler interest:

  • 10 Year Warranty
  • Cylinder loading system (CLS) and integrated stainless steel storage tank
  • User friendly control via backlit LCD touchscreen
  • High hot water capability of >18 litres per minute
  • Large range of outputs available
  • Optional wireless remote available

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Now you know our favourite combi boilers of 2021, for more information on which combi boiler may be best for you, feel free to give us a call on 0333 305 6880 or use our bespoke boiler quote service which will automatically recommend the best combi boiler for you and your household.

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