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Best combi boilers 2021 | Independent & impartial


Jo Alsop

Heating Hero

The Heating Hub

Which are the best boilers based on their technical merits? We review here.


Best combi boilers

Most 'best boiler' blogs are written by boiler installation companies that have a vested interest in ranking top the boilers they fit, which is based on financial rebates they receive from fitting them. It means that consumers never get a clear view of the market and the best option for their budget.

We are fully independent and impartial and act in the best interests of consumers first and foremost. Our judging criteria is based primarily on the technical merits of the boiler and how efficiently it can operate all year round. When we ignore brand strength and marketing blurb, we can offer you a clear picture of good and average products with some interesting results. We've found budget boilers that are technically better than many well known models and some lessor known brands that outperform household names.


  1. How we judge our combi boilers
  2. Warning label
  3. Best combi boilers by price group: budget, mid-range and premium
  4. Five steps to finding the best combi boiler
  5. The best combi boiler is only as good as your heating control
  6. Getting the best from your combi boiler
  7. Are combi boilers suitable for larger homes?

1) How we judge our combi boilers

First and foremost we look at the technical merits of the boiler and how well it can be adjusted to the heating system by a competent engineer. We balance this to a lessor extent against warranty and price to find all round good value.

a) How low the boiler can go. All boilers operate within a range of outputs. For example 2-20kW or 8-30kW. The lower the boiler can go, for example 2kW in these examples, the more efficiently it can operate all year round. The average heat requirement for the majority of UK homes is 6-8kW on a very cold day. The boiler models with a lower output can operate efficiently during milder weather. There are other criteria also, but too lengthy to go into here.

b) Value for money - we also consider the cost of the boiler against the warranty length and efficiency capacity. This means we can recommend some very reasonably priced boilers with better efficiency potential than more expensive models.

c) Warranty period - some manufacturers offer the same boiler with different warranty periods, for example 2 years or 7 years. The 7 year warranty model will be more expensive. We weigh up these packaged up boilers against other manufacturers of a similar price and cover.

2) Warning label

We want to answer the question of 'which is the best combi boiler' honestly and provide meaningful advice to you. However we have to do so with a warning label, because some much of the performance of the boiler in the home comes down to two things:

a) how well the installer can set it up

b) the heating control it has been paired with

So that even technically 'the best' boiler will perform poorly in the home if it is not set up correctly and/or fitted with a basic control. 99% of installers have not been trained to set up a condensing boiler correctly so most best boilers do not reach their potential. (You can access the 1% who can via our Elite Installer Network.)

3) Best combi boilers by price group

We have selected the top-performing boilers that come with great all-round value for budget, mid-range and high-end models. We have found that the most expensive is not always the best! In each category there is a boiler to suit you. Some lesser-known brands have made it into the top 3 or 4 on their merits, but if you prefer a more familiar brand then you can choose from one of the others in the category.

Best combi boilers on a budget

Budget boiler does not mean bad boiler! We have found four excellent, cost-effective options that offer very decent warranties and efficiencies for a low price. The lower the minimum output of the boiler the more efficiently it can operate all year round. The Ravenheat boiler outperforms some much more expensive models (not featured on this page of course, we only show the best of the best in class) with some more well known brands coming in just a little higher


Goes to Ravenheat HE80. Great price, great minimum output.


Goes to Alpha Evoke. Low price + 5 year warranty.


Is the Glow Worm Energy. Best warranty in the pack.

Rank Boiler Cupboard fit Boiler cost Manufacturer Cover Maximum output Minimum output Litres per minute hot water
1 Ravenheat HE80 Y £649 5 25kW 3.6kW 10.2
2 Alpha Evoke Y £700 7 28kW 4.3kW 12.1
3 Glow Worm Energy Y £700 7 19kW 5.0kW 12.1


Best mid-range combi boilers

The mid-range category is a big one with prices ranging from £780 to over £1,100 without any clear pattern in terms of performance or warranty. We have selected models with the lowest outputs combined with a great all-round package of aftersales care. Here is our pick of the best:


Goes to Intergas Xclusive. Great price, great minimum output.


Is the Vaillant Ecotec Plus. A 10 warranty from this familiar brand.


Is the Viessmann 100-W. Great all round package

Rank Boiler Cupboard fit Boiler cost Manufacturer Cover Maximum output Minimum output Litres per minute hot water
1 Intergas Xclusive 24 Y £969 10 19kW 3.6kW 10.1
2 Vaillant EcoTec Plus Y £1,145 10 21kW 3.8kW 10.5
4 Viessmann 100-W N £1,070 5-7 26kW 4.7kW 8.9


Best premium combi boilers

When prices go up we've made sure there is more value. Each of the boilers below comes with up to 10 years of warranty (NB some boilers must be fitted by an approved installer in order to qualify) plus some very low minimum outputs. Remember the lower the boiler can go, the more efficient it can be.


Goes to Viessmann Vitodens 200. Best minimum output on the market.


Goes to Worcester 8000. Low minimum output + 10 year warranty.


Is the Vaillant ecoTEC Green iQ. Low output plus 10 warranty from this familiar brand.


Is the Intergas Xtreme. Great all round package and low price

Rank Boiler Cupboard fit Boiler cost Manufacturer Cover Maximum output Minimum output Litres per minute hot water
1 Viessmann Vitoden 200-W N £1,602 2-5 25kW 1.9kW 15.7
2 Worcester Bosch 8000 30 N £1,275 5-10 30kW 3.0kW 12.3
3 Vaillant ecoTEC Green iQ N £1,651 5-10 24Kw 3.4kW 14.5
4 Intergas Xtreme N £1,268 7 30kW 3.6kW 13.3


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4) Steps to finding the best combi boiler for you

a) Low minimum output

All boilers operate in a range of outputs, for example, 2-20kW or 6-18kW. The lower the minimum output, the more efficiently the boiler can operate all year round. There are some great high efficiency boilers, often at great prices, from lesser-known brands such as Ravenheat and Intergas. Lower fuel bills are always a priority, as is warranty length and sometimes brand familiarity. We have put forward boilers with the lowest minimum outputs on the market so you can pick according to your other priorities.

b) Size your hot water requirements

Hot water performance is expressed in litres per minute (LPM) – this is how fast the boiler can heat cold water. The smaller boilers will always be around 10 litres per minute, the bigger boilers over 16 litres per minute. Litres per minute is important if you and your family have multiple bathrooms and shower at the same time in the mornings. The problem with combi boilers that give bigger hot water outputs is that they are too often oversized for the heating system - which is very inefficient. Don't worry, we have only featured boilers that can give a low minimum output alongside great hot water performance.

c) Do you need a cupboard fit?

If you are installing your new combi boiler in a kitchen cupboard you will need a compact boiler. However this are only available in the smaller models.

d) Is the warranty length important?

If you are moving in a few years perhaps you do not need one of the more expensive boilers with a 10 year warranty; a budget end boiler with 5 a year warranty will do and save you £500.

e) What is your budget?

There are some great value boilers even at the lower end. Work within your budget to find a boiler with the longest warranty.

5) The best combi boiler is only as good as the heating control

The efficiency of modern condensing boilers comes partly from their ability to operate at low outputs during warmer weathers, hence why a low minimum output is so important. When your home requires just 1-2kW of heat, as it often does, a boiler than can only go down a low 7kW is going to be oversized for much of the year. A boiler than can go down to 2kW will have the efficiency advantage.

However, in order for the boiler to reduce down to 2kW it must be paired with a compatible control, known as a compensation control. These must speak the same language as the boiler. To find a compatible control for your high efficiency boiler see our Guide to advanced heating controls.

6) Getting the best from your combi boiler

Stated outputs for combi boilers are 24kW and upwards. However this high kW output is for hot water production. For heating, the kW outputs are lower but not by much. The smaller combi boilers start at 18kW which is still three times the size of most homes on a very cold day.

For combi boilers it is best to factor hot water production into your decision and just make sure the boiler, whichever one you pick, can be adjusted down to meet your heat requirement. This must be done by a competent gas safe registered engineer. If you have multiple bathrooms in use at the same time opt for a system boiler with hot water cylinder. For more on boiler sizing try our Guide to sizing your boiler.

7) Are combi boilers suitable for larger homes?

Even a big combi can only do so much and the bigger you go the more the boiler is oversized the boiler can be for heating. If you have two or more bathrooms that are often in use simultaneously then you may want to consider a system boiler with hot water tank (assuming your water pressure is good enough). For more help with choosing the right boiler for a larger home, including the careful selection of a combi boiler, read our Guide to combis for larger homes.


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