The Best Combi Boilers in the UK in 2021

The top 5 best combi boilers in the UK, right now in 2021.

Combi boilers are the types of boilers most regularly installed when housebuilders are constructing the new homes and apartments we live in. Likewise, for homeowners and landlords investing in a new boiler for their existing properties, combi boilers are the most popular choice by some distance.

We’ve already looked at what the best boilers of any type are in 2021. But what about the top 5 gas combi boilers in the UK right now? There over 206 to choose from in the UK – it’s a very competitive marketplace – with the average price of a new boiler costing £1,098.

In this article, we’re looking at the best of the best. We’ve scored each of the 206 boilers we’ve reviewed and come out with a best in class for each manufacturer. We then compare each manufacturer’s best offerings against each other to provide you with a guide on the boiler for your size of home.

In this article, HomeSage looks at:

• what a combi boiler actually is
• gas combi boilers versus electric combi boilers
• the key statistics to look out for when choosing a combi boiler
• the exclusive HomeSage boiler scoring system and how it works
• the top 5 small gas combi boiler in Britain
• the top 5 medium gas combi boilers in the UK
• the top 5 large gas combi boilers as evaluated by the HomeSage scoring system
• more about our service

Want to save up to 30% (and sometimes more) on the supply and installation of a new boiler for your home? Simply fill in the form at the top of the page – leave your details with us and we’ll pass them on to 3 or 4 trusted Gas Safe traders in your area.

What is a combi boiler?

It’s no secret to most people that the average size of new homes and apartments in Britain has reduced decade by decade since the Second World War. As a result, Britons now pay more per square foot of property they inhabit in either mortgage payments or in rent than almost every other country in the world.

Traditional/system boilers still require the installation of one or two massive cylinders either to heat the water we use in our radiators and which comes through our taps. In most new developments and in most standard housing developments over the last 30-40 years, there just isn’t room for them anymore.

In response to this, manufacturers created the combi boiler. A combi boiler heats water up on demand when we need it for our radiators, for our baths, and for when we need to do the washing up. A combi boiler is a standalone unit often small enough to hide in a cupboard or a cabinet in our kitchens or our bathrooms.

Gas combi boilers vs electric combi boilers

There are two main types of combi boiler – combi boilers powered by gas and combi boilers provided by electricity.

For most people whose homes receive a gas supply, they find the best combi boiler for them is a gas one, because the running costs are much cheaper.

Let’s take a standard 24kW output combi boiler as an example. A boiler with this output requires 24 units of gas or 24 units of electricity to power it for an hour. You might pay as little as 4p per unit with gas and up to as much as 15p per unit with electricity. In other words, an electric combi boiler will cost you nearly four times as much to run as a gas boiler.

As part of the government’s drive to reduce carbon dioxide greenhouse gas emissions by 2050, they look certain to ban the installation of gas combi boilers within new build properties in 2025.

Key things to look for when selecting the best combi boiler

There are five key factors to think about when you’re considering a new gas combi boiler for your home. In most cases, you can save yourself from the possibility of choosing the wrong boiler by speaking with a Gas Safe installer prior to make a decision.

The five key factors are:

• your boiler’s output rate
• its flow rate in litres per minute
• its size
• how energy efficiency your boiler is
• the length of a manufacturer’s warranty

The output rate

The output rate describes the maximum amount of energy that your boiler uses when heating water for either your radiators of for your hot water taps. The higher the output rate, the more water it can turn from hot to cold on demand.

There are three main output bands you need to know about – 24kw-27kw, 28kw-34kw, and 35kw and above. Depending on the size and configuration of your property, you’ll need to select the right output level.

If you choose too high an output level, you’ll get all the hot water and warmth you need (subject to flow rate) but you’ll pay too much in running costs. If you choose too low an output level, you’ll save money but your boiler will struggle to cope if you want to run two hot taps at the same time, for example.

The flow rate

The flow rate of a boiler is closely linked to its output rate. The flow rate describes just how much water can pass through the boiler within a minute. The bigger your property, the greater the flow rate you should choose.

The size

The sizes refers to the physical dimensions of your boiler. As we mentioned earlier, some boilers are small enough to conceal completely within a cabinet or cupboard within a bathroom or a kitchen. Others will require installing in somewhere like a utility room and they’ll be too big to hide.

For reference, out of the 206 boilers we rated for this article, 205 of them are wall-mounted – only one of them, the Worcester Bosch Greenstar Highflow 550CDi boiler, is floor-standing. In addition, all of the combi reviewed in this piece are designed for internal use (fitted indoors) and not external use (fitted in the open air within the boundaries of your property).

How energy efficient a boiler is

Energy efficiency measures how much of the power your boiler uses to provide warmth and warm water to your home. The more energy efficient, the fewer units of gas are wasted in non-primary functions when your boiler is in use.

All of the boilers reviewed in this article are either A-graded (90% of more of energy expended is in the provision of heat and hot water) or B-graded (80-90% although most of them are just a fraction off 90%).

The manufacturer’s warranty

You should expect, as a minimum, to enjoy 10 years’ full usage from your boiler following the date of installation. Boiler manufacturers provide between 2 years and 12 years’ warranty (although you must write into each manufacturer to turn the initial 12 months warranty period into the longer warranty).

The exclusive HomeSage boiler scoring system

For this article, HomeSage has rated each boiler with its unique scoring system to provide you with guidance on whether we think a boiler represents value for money or not. The score is given as a percentage.

The weightings we have used for the scores are:

• 1/6 for manufacturer reviews on TrustPilot (1/12 for number, 1/12 for average score)
• 1/6 for fuel type
• 1/3 for energy band ratings and efficiency ratings
• 1/6 for price (prior to installation)
• 1/6 for length of warranty offered

The best combi boilers – top 5 small combi boilers (24kW to 27kW)

If you have a smaller home like an apartment or a mid-terraced property, your installer is likely to recommend that you select a combi boiler whose output level ranges between 24kW and 27kW.

There are currently 65 models on the market with an average price of £975 including VAT.

1. Baxi Platinum 24 Boiler (92.69%)

The Baxi Platinum 24 boiler is, according to our scoring system, the best gas combi boiler for small premises. Baxi’s customers lover them, scoring them very highly across over 16,000 reviews. Price-wise, it comes in at around £100 cheaper than the average boiler for a house this size and there’s a ten year warranty on it too. Size-wise, it’s 450mm by 780mm by 345mm so it’ll be easy for your installer to conceal it.

2. Worcester Bosch 2000 25 Boiler (91.89%)

Manufactured by one of the most famous brand names in the UK, second place belongs to the Worcester Bosch 2000 25 boiler. The 2000 25kw boiler only comes with a 5 year warranty unfortunately but the company manufactures to such a high level, you’re almost guaranteed to get a good decade of use out of the boiler. It’s also very small at just 400mm by 724mm by 300mm.

3. Vaillant ecoTEC plus 832 Boiler (86.83%)

The third-best combi boiler of the smaller size comes from one of Britain’s biggest supplier of boilers by volume with its Vaillant ecoTEC plus 832 boiler. Its flow rate is very impressive meaning that it should handle with ease the supply of hot water to two taps – quite often a bugbear with many homeowners. 

4. Glow-worm Logic Plus C35 Boiler (85.01%)

Fourth place is taken by one of the UK’s most respected boiler manufacturers, Glow-worm. The Glow-worm Logic Plus C35 boiler has earned its place because of the esteem in which both customers and installers hold the quality of the company’s products, its high flow rate for a boiler this size, and its generous 7 year warranty.

5. Ideal Vogue GEN2 C32 Boiler (83.89%)

The Ideal Vogue Max C32 boiler makes it into fifth place. Measuring just 445mm by 740mm by 330mm, its eight year warranty is a real show of confidence from the company in the reliability and longevity of its products. It’s quite a bit more expensive than the average boiler for a small house and that’s the primary reason that this superb piece of equipment did not rank higher in this best-of-the-best league table.

The best combi boilers – top 5 medium combi boilers (28kW to 34kW)

An installer will recommend a combi boiler with an output of 28kW and 34kW if you live in a mid-sized property with 1 or 2 bathrooms, 2-3 bedrooms, and up to 15 radiators.

There are currently 84 gas-powered combi boilers on the market whose output is between and the average price before installation for a boiler of this size is £1,002 including VAT.

You’ll notice from these models that many of them are the bigger brother or sister of the models in the 24-27kW range – they offer all the same benefits except they provide beefier output and higher flow rates.

1. Baxi Platinum 28 Boiler (92.36%)

The Baxi Platinum 28 boiler makes it into first place – this is the sister boiler of the Platinum 24 which finished in first place for the smaller property category (24-27kW). It’s priced at the market average which you’d expect to pay for a boiler for a medium sized property so you won’t make any savings from choosing this boiler. However, we love the 10 year piece of mind guarantee and that’s what swung it in the end.

2. Worcester Bosch 2000 30 Boiler (91.62%)

The Worcester Bosch 2000 30 boiler powers into second place and this is also the sister boiler to the runner up in the 24-27kW category, It’s essentially the same model but with more output power and a higher flow rate. At nearly 15% below the average price for a medium-sized-property boiler, this represents a real bargain.

3. Vaillant ecoTEC plus 838 Boiler (86.45%)

In third place comes the Vaillant ecoTEC plus 838 boiler retailing from £1,380. The high flow rate of its sister model (the 832 boiler) from the 24-27kW category is substantially increased on this larger model – 15.9 litres per second.

4. Glow-worm Ultimate3 30 Boiler (85.82%)

The Glow-worm Ultimate3 30 boiler’s requirement of just 30kW to operate is great for running costs. We also love its 10 year warranty and its price – around 30% cheaper than the average for a medium-sized-property boiler.

5. Vokera Evolve C 28 Boiler (82.86%)

The Vokera Evolve C 28 boiler comes with a substantial seven year warranty and its priced at around 15% below the average market price for a 28-34kW boiler. Its energy efficiency rating is particularly high although we wish its flow rate was a little bit higher.

The best combi boilers – top 5 large combi boilers (35kW and over)

For larger homes, an installer will either recommend a combi boiler or a regular boiler whose output is 35kW or higher.

There are currently 49 large gas-powered combi boilers on the market with an average supply-only price of £1,370.

1. Baxi 636 Boiler (92.43%)

Finishing in first place is the Baxi 636 boiler – for a boiler capable of powering multiple radiators and taps at the same time, its small size of 700mm by 390mm by 285mm is surprising.

A seven year warranty coupled with the fact that it’s nearly 25% cheaper than most big capacity boilers and great customer feedback makes this our number one overall for 35kW+ output boilers.

2. Worcester Bosch Greenstar 8000 Life 35 Boiler (90.59%)

Using the HomeSage scoring system, a brand-leading competitor occupies second top spot with the Worcester Bosch Greenstar 8000 Life 35 boiler. A five year warranty coupled with an economical output rate for a boiler with this flow rate tipped its HomeSage rating about 90%. What stopped it from hitting top spot was the price – at nearly £300 more than the Baxi 636, we struggle to justify why you should pay £300 for an extra 2 year’s warranty.

3. Vaillant EcoTEC Exclusive Green IQ 843 Boiler (85.81%)

The Vaillant EcoTEC Exclusive Green IQ 843 boiler measures a bit bigger than we like – 440mm by 720mm by 474mm, it’s a bit bigger. It’s also £600+ more than Baxi’s effort for a shorter warranty and similar annual running costs. However, it’s a very impressive boiler with a very generous flow rate hence its 85%+ rating.

4. Glow-worm Ultimate3 35 Boiler (85.64%)

In fourth place, the Glow-worm Ultimate3 35 boiler comes with a 10 year warranty and it’s available at a price up to 40% cheaper than the average large-property combi boiler. We wish it were just a bit more energy efficient and its flow rate was greater. That said, homeowners and landlords are unlikely to be disappointed if they purchase this model.

5. Vokera Evolve C 35 Boiler (82.60%)

In fifth place, you will still have change from £1,000 from most tradesmen (before installation costs) from the Vokera Evolve C 35 boiler. We like its extended warranty, its generous flow rate for the price, and its compact dimensions of 740mm by 420mm by 350mm.

Save up to 54% of the cost of installing your new boiler

To save up to 54% on the installed price of your best boiler from the above list, please fill in the form at the top of the page. We’ll then send your details to multiple local trusted Gas Safe engineers. You’ll get a call back with a quote and they’ll talk through with you which is the best combi boiler to provide your home and your family with the hot water and heat you need, exactly when you need it.

There’s no cost to our free service and you’re under no obligation to accept any of the offers made by our partner installers.