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The Best Combi Boiler in the UK (Reviews) for 2021

To find the best combi boiler we had to run numerous tests, dig deep into specifications, warranty sheets and reviews from people who own the products we feature. We sat down with local engineers to understand what makes a combi boiler better than the other and what customers must know to make an informed decision.

Our boiler analysis took months of research but we’re proud to say that we know combi boilers inside and out and can give you a rundown on the important aspects, like the big warranty guide we’ve assembled towards the end of this buying guide.

Too busy reading through this review, here’s the shortened version:

What are the best small/medium combi boilers?

  1. Worcester Greenstar 25i
  2. Viessmann Vitodens 050-W 29kW
  3. Baxi Duo-tec 24 – 24kW / 30kW

What are the best large combi boilers?

  1. Worcester Greenstar 34 CDI
  2. Viessmann Vitodens 100-W 35kW
  3. Ideal Boilers Vogue 40

What highly powerful model is the best combi boiler?

  1. Worcester Greenstar 42CDI
  2. Viessmann Vitodens 111-W 35kW
  3. Ideal Boilers Vogue C40 Gen2

The best combi boilers: How we tested

As a homeowner, there’s one thing you need to focus on when choosing the best combi boiler, and that’s the warranty.

More specifically. How you get that warranty (it’s not as simple as it seems).

You’ll see from our warranty guide, we rate leading boiler brands such as Baxi, Ideal Boilers and Worcester Bosch.

Check the combi boiler warranty

We know a lot of the decision-making process comes down to price, especially when you throw in budget boiler brands into the mix.

However, something worth considering, is that Bosch have streamlined their sales process by working with online boiler installation platforms like HEATABLE. They  (presumably) supply the boilers at preferential rates, meaning the overall installation cost from their platform is ridiculously low, when compared with other premium combi boiler brands.

To see what I mean, you can jump online and get a fixed price in around 2 minutes. Here’s the one we just got:

The best combi boiler brand?

As we’ve said, the focus should be on the combi boiler warranty. Typically, we’d want to see a minimum of 5-year warranty on any boiler installation, but remember, there are plenty of boilers on offer with 7-years upwards.

Deciding on which is the best combi boiler is up for debate, and one installer’s opinion is going to differ from the next. However, here are two combi boiler brands that are certainly worth mentioning.

1. Worcester Bosch Combi Boilers

Worcester Bosch are one of the best combi boilers money can buy, and they’re by far the most popular in the UK. At my time spent working in a plumbing merchant, we’d sell at least two Worcester boilers, for every one of every other brand combined.

They’re efficient, reliable and recommended by most boiler installers. More importantly, they’re available with a warranty of up to 10-years, which is huge!

The main let down used to be the price, which typically was at the higher end for combi boilers.

However, Bosch are now working with the biggest online boiler installation companies, supplying Worcester combi boilers extremely cheap. That saving is being past on the end consumer, you!

It’s easy to get a fixed boiler price on-screen (without putting in any personal details or annoying call backs), by filling out this on-screen form.

2. Viessmann Combi Boilers

Renowned for their German strictness, Viessmann are a producer that is synonymous with high-quality manufacturing. We also know that Viessmann’s combi boilers are also renowned for being highly efficient (A-rated), making them extremely friendly with your pocket in the cold months.

But why are Viessmann boilers so cheap considering they’re perceived as a premium brand, you may ask?

The company’s approach for the UK boiler market is to promote its flagship models at highly attractive prices, get homeowners happy for fitting an excellent product in their homes and slowly gain more slices of the boiler pie.

3. Ideal Combi Boilers

Ideal combi boilers are typically cheaper than Worcester’s from your average installer, but that doesn’t mean quality is compromised.

Something like the Ideal Logic Plus boiler with a 7-year warranty, will be comparable in price to the Worcester 25i or 30i, when installed by online boiler installation companies. And that’s simply because they push the Worcester boilers at volume, so are able to offer them at preferential rates, complete with an extra 3-years warranty.

4. Vaillant Combi Boilers

Some would argue how big of a player Vaillant is in the UK boiler market.

But we’re not comparing combi boiler brands by their size, therefore we think it’s more important for homeowners to fit a product that follows the most rigorous build standards, packs premium components, is durable and doesn’t break the bank. Except that, in truth, Vaillant won’t be that friendly with your finances at first.

Proud holder of a Which? Best Buy award in 2017, Vaillant made sure the quality of its products is well reflected in the final sale price.

Their ecoTEC plus boiler is the company’s flagship model. They start from 25kW making it an excellent choice for a small to medium household who can afford the premium to acquire it.

5. Baxi Combi Boilers

Baxi is the best budget combi boiler option here. Although Baxi may not struck you as a premium brand in the market, their boilers are nothing short of durable.

The company has been worked hard at building a great reputation by offering award-winning customer support, efficiency and amazing warranties for its extensive lineup ot innovative combi boilers.

Their Baxi 600 and Duo-tec boiler range comes with an extensive 7-year warranty, matching the Ideal Logic Plus. While the Premium, Premium+ and EcoBlue Advance match the Worcester Bosch boilers with a 10-year warranty attached. Baxi

Our advice is to stay away from boilers with less than 7-year warranty, so consider avoiding the Baxi 100, 200 & 400 range if you want a higher quality product with an excellent warranty.

Would you like to compare boiler prices back to back? Use this quick on-screen form.

Combi boiler sizing

Best combi boiler for 1-2 bed properties

Brand Model Warranty Price (installed)
Worcester Bosch Greenstar 25i 5-8 years from £1,770*
Worcester Bosch 28, 32 and 36CDI Compact 5-10 years from £2,050*
Viessmann Vitodens 050-W 29kW 10 years from £1,670*
Ideal Boilers Logic+ 24 7 years £1,750
Ideal Boilers Vogue 26 10 years when fitted with an Ideal system filter £1,900
Ideal Boilers I-Mini 24kw 2 years £1,650
Baxi Duo-tec 24 7 years £1,700

* prices available from HEATABLE

Best combi boiler for 3-4 bed properties

Brand Model Warranty Price (installed)
Worcester Bosch Greenstar 30i 5-10 years from £1,969*
Worcester Bosch Greenstar 34CDI 5-10 years from £2,100*
Viessmann Vitodens 050-W 35kW 10 years from £1,964*
Viessmann Vitodens 100-W 30kW 10 years from £2,119*
Ideal Boilers Logic+ 30 7 years £1,850
Ideal Boilers Vogue 32 10 years when fitted with an Ideal system filter £2,100
Baxi Duo-tec 28 7 years £1,850

* prices available from HEATABLE

Best combi boiler for 4-5 bed properties

Brand Model Warranty Price (installed)
Worcester Bosch Greenstar 42CDI 5-10 years from £2,750*
Viessmann Vitodens 100-W 30kW 10 years from £2,169*
Ideal Boilers Vogue C40 Gen2 10 years £2,400
Ideal Boilers Logic+ 35 7 years £2,200
Baxi EcoBlue Advance 10 years £2,100

* prices available from HEATABLE

Installation prices are estimates. Worcester boiler prices represent estimates for local installers, but tend to be much cheaper from HEATABLE given they’re one of UK’s largest installer.

See our boiler installation guide if you are having your boiler replaced.

What is the best combi boiler?

#1 – Worcester Greenstar I Combi Boilers

Let’s face it…when you think boiler, you think Worcester Bosch. 

At my time working at a local plumbing merchant, we were knocking out so many Worcester boilers, we’d get a full lorry load delivered every month, and “top-ups” daily; that was just one branch.

So, why do we think it’s the best combi-boiler, and should you install one?


The most popular models in the range, are the 25i and 30i combi boilers. But, there’s also a range of system and regular I boilers too.

When they’re running almost flat out, they’ll be giving around 87.7% efficiency, or up to 99.4% when running at around 30% of their maximum output.

In comparison to an old boiler, that’s going to be saving you BIG money on your gas bills.

Installation isn’t as expensive as you think

Worcester boilers are typically known as a premium brand, with a price tag to match. Well, that was until Bosch changed all that, by investing in supplying (in a more streamlined way) boilers to online installation companies, like HEATABLE.

A normal Worcester installation from a local engineer is likely to be £200 more expensive than the equivalent from Ideal’s range. That only rises (considerably) when you choose a national installer, running TV ads and the likes.

But, compare that with HEATABLE. We’d expect a 25i to sit in the £1,900-£2,000 range. Yet, on a 25i, here’s the quote we just got (you can get yours within 90 seconds here).

Worcester Bosch Greenstar i from Heatable

The warranty is huge

You can get up to 10 years warranty on the Greenstar I range; there are very few boilers, or boiler manufacturers, offering this level of warranty.

Like we mention in most boiler reviews, the best combi boilers have a long warranty. Why? The warranty being offered by a manufacturer is, essentially them telling you how good they think their boiler really is.

Short boiler warranty = “It’s probably going to break, and we don’t want to pay to fix it”

Long boiler warranty = “This boiler has longevity, so we have the confidence we won’t have to pay to fix it”

Even if they’re wrong, there’s one person that doesn’t have to pay for those repairs; YOU!

It won’t self-destruct in winter

In the first year of this site being launched, we were averaging around 400-500 visits a day. Breaking into the second year, that started rising…then the temperature dropped below zero, for like 5 days straight.

At its peak, the site got over 19,000 visitors in a single day. My guestimate is most of these homeowners were searching how to fix a frozen condensate pipe; it’s a common boiler problem in winter.

That’s why Worcester have introduced preventative measures, such as the CondenseSure. This protects your boiler down to a stated -15.

So, unless you’re waving from the Arctic, you shouldn’t have issues with your condensate pipe freezing with a Greenstar I.

But, we don’t like this

There’s no rose without a thorn, and in my opinion, that’s the case here. I like compact boilers. You’ve got more flexibility on the installation space you can use.

If you’re not planning to move your boiler, and it lives in an airing cupboard or is wall-hung, you’re all good with the Greenstar I.

However, if you want to tuck your boiler away in a small space (such as a kitchen cupboard), this isn’t the boiler for you; it’s too big.

But, where there’s a will, there’s a way. If you need a compact Worcester boiler, you can head for the SI Compact instead.

Should you install the Greenstar I?

Yes, but which one? Each property is unique. Your property might have a longer heating run, more radiators, or even better insulation than the average. There’s not a one-size-fits-all.

The best thing to do? Grab a cuppa’, put aside around 90 seconds of your day and fill out this clickable multiple choice questionnaire over at HEATABLE.

You won’t need any personal details (postcode, phone number etc), and you’ll have a fixed price as well as your recommended boiler at the end, for your efforts!

#2 – Viessmann Vitodens Combi Boilers

We said it before, Viessmann combi boiler are German design at its best.

Viessmann Vitodens 050-W Combi BoilerTheir flagship models, the Vitodens range, include the Vitodens 050-W in two flavors (29kW and 35kw) and the more powerful VItodens 100-W. But why did they make our list?


We’re talking a class A rating for efficiency. And if you’re at least a bit concerned about the quality of our lives on Earth, learn that the Vitodens range promise low CO2 emissions to help ease your carbon footprint.

That means you could save about £350 and 1,500kg of carbon monoxide a year.

Installation costs

A new Viessmann 050-W boiler from HEATABLE comes with a fixed price of £1,670. That happens all online, and if you do it before 3PM, you get next day install, too. Why are we telling you all this? Because everyone expects premium quality and premium prices.

That’s not the case with the 050-W. The price includes free wireless heating controls, a free system cleanse and an Adey Sense filter. It’s a bargain if you compare it with other premium combi-boilers.

Viessmann Vitodens 050-W from Heatable

Warranty: 10-years

Because Viessmann only knows to use high-quality components, it makes sense their boilers will stand the test of time.

That’s why the German producer is able to offer an exclusive 10-years warrant through Heatable for their fitted products. It’s the highest warranty you’ll get for a combi boiler.

Should I get a Viessmann Vitodens boiler?

The answer is a strong yes. But since each property is unique, we advise you to check out which model is the right one for you. Heatable has an online form that will take you only a couple of minutes to fill.

There’s no personal information that you need to provide other than your postcode and the type of house and installation.

#3 – Baxi Duo-tec & EcoBlue Advance Combi Boilers

Baxi is a budget option but not because they sacrifice quality over affordable pricing. There are two models we recommend based on your space, which like all Baxi products are built in the UK.

Baxi EcoBlue Advance combi boilerFor small to medium homes the Duo-tec promises up to 40kW providing 16.4 litres/minute hot water. That’s exceptional hot water performance if you ask me.

For larger homes, the more powerful EcoBlue Advance promises instant water while at the same time meeting the minimum energy efficiency rating required for Boiler Plus compliance.


There’s not much to say about the efficiency of the Baxi boilers. all models get a straight A for both running water and heating. So your conscious is at peace for doing a good deed.

Installation costs

A new Baxi Duo-tec 28 costs around £1,700 while the Duo-tec 28 is another £150 – £200.

That’s really affordable.


If using Baxi approved Gas safe engineers, the Duo-tec range gets a 7-years warranty while the EcoBlue Advance a whopping 10-years warranty.

Should I get a Baxi boiler?

Baxi builds quality products, don’t forget. They have an affordable price tag, but they still are quality products with excellent warranty terms. So our advice is yes, you are acquiring piece of mind when buying a Baxi combi boiler, be it the Duo-tec or the EcoBlue Advance range.

#4 – Ideal Vogue Combi Boilers

There’s not much to say about Ideal Boilers except that they have been a player in the market for almost as long as we know the market 🙂 Vogue range is their premium lineup of combi boilers, built with utmost care for perfection.

Ideal Vogue Gen2 Combi BoilerEfficiency

Straight A for both running water and heating. It’s also Energy Saving Trust endorsed.

Installation costs

The Vogue 26 will set you back some £1,900, the Vogue 32 around £2,100 while the flagship Vogue C40 Gen2 will be around £2,400.

Warranty: 10-years

The Vogue range comes with a 10 year parts and labour warranty. That and the fact that Ideal Boilers are serious about providing high quality to homeowners has gotten them the Good Housekeeping Reader Recommended status in 2013 and 2017.

The only thing you should be aware of is you get the 10-years warranty if it’s installed with an Ideal System filter.


  • Frost protection
  • Very quiet (award-winning design)
  • Backlit 3.5″ LCD full colour display.

Should I get an Ideal Vogue boiler?

The short answer is yes. The long answer is … we would personally go with a Worcester Bosch or a Viessman Vitodens for delivering more piece of mind, but getting the Ideal Vogue Gen2 combi boiler is not a bad deal at all.

Combi boilers warranty guide

I’m going to tell you right now. Warranties are confusing, even from the best boiler manufacturers. We’ve already mentioned accredited installer networks. And that usually gives a buyer access to extra warranty.

Some manufacturers will then charge for additional warranty.

Always double check warranties before purchasing. Top boiler manufacturers regularly run promotions (including extended warranties), so they do change from time to time.

The warranty may just be the deciding factor in which is the best combi boiler for your home.

The combi boiler fine print to care for

Warranty terms and conditions are always extensive. However, these are the most important things you’ll want to consider to meet the T&Cs of your boiler warranty:

  • Register your warranty within 30 days
  • Installation has to be by a Gas Safe engineer
  • Some brands may require you use an installer from their network to gain access to additional warranty
  • Annual servicing from a Gas Safe engineer

And here are common things in T&Cs from most manufacturers that void a warranty:

  • Scale build up (typical in hard water areas, combat this issue by installing a lime scale inhibitor)
  • Sludge build up in a system (combat this issue by installing a magnetic system filter and having it cleaned out with every service)

Worcester Bosch: Warranty Explained

Most Worcester installers hype the 10-year warranty on offer, but not all Worcester boilers come with a 10-year warranty as standard. There are companies like HEATABLE that offer 10-years on all products, as they have a special relationship with Worcester.

You’ll get up to 10-years warranty on the CDI range (using an accredited installer).

A Gas Safe engineer in the Worcester Bosch accredited installer network will allow you to get that little bit more in terms of warranty on other ranges too.

Installation details CDI Range I Range SI Range
Worcester boiler only 5 years 5 years 5 years
With accredited installer 7 years 7 years 7 years
Worcester boiler, and branded magnetic system filter 6 years 6 years 6 years
With accredited installer 8 years 8 years 8 years
Worcester boiler, filter branded controls 7 years 6 years 7 years
With accredited installer 10 years 8 years 9 years

Straight up, Worcester branded parts are not cheap. To get their extended warranty, you have to buy them!

The Worcester system filter will cost more than £130.

An equivalent from Adey (they specialise in filters and chemicals) will cost around £100.00.

The Worcester Wave timer will cost around £225. Whereas the Nest (company owned by Google) Smart Thermostat will cost less than £200.

The finer details of the Worcester Bosch boiler warranty can be found here.

Ideal Boilers: Warranty Explained

Ideal’s warranty is, well, Ideal. It’s just so simple.

Right now, they do have an installer network, but they recognise that Gas Safe set the standard for installers, and not their network (i.e. you can use any Gas Safe registered installer to get their warranty).

Here is what their warranty looks like.

Product Warranty
Ideal Instinct 2 years
Ideal Logic 2 years
Ideal Logic Plus 7 years
Ideal Vogue 10 years

The make sure you don’t break their T&Cs. Have a quick look here.

Baxi Boilers: Warranty Explained

Product Warranty
Duo-tec 7 years
Platinum Combi 10 years

Baxi do have an installer network, but any Gas Safe registered engineer can be the installer.

“The installer must be registered with Gas Safe and complete the Benchmark commissioning checklist in full at the time the boiler is installed. This checklist must be made available to us if we ask and is found at the back of the installation instructions.”

Baxi’s warranty T&Cs are here.

What is your next step now that you’ve read our best combi boiler guide?

Hopefully our guide to the best combi boiler gives you all the information you need to know to make a decision on which brand to buy.

Still confused by which is the best combi boiler brands?

Skip over to our boiler installation cost guide. Or, drop us a line through our contact form or in the comments below, and we’ll do our best to help you out.

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  1. The Worcester Bosch Greenstar range is by far the most popular choice with any boiler installer I’ve spoken to recently. The warranty shows the brands confidence in the build quality and parts used in the boilers. They are just unfortunately not affordable for all unless finance options are an option.

  2. Local Authority Eco Scheme Energy Company Obligations (ECO) offering replacement Potterton boiler with 2-year Warranty. Our present boiler is a Worcester Greenstar 37CDi Combi which is 12 years old but has a new Heat Exchanger installed last year and we have a British Gas Maintenance contract. We want to know if we should stick or twist as suggestion is that the present boiler might only last another 3 years. Advice would be helpful.Thanks.JMCD

    1. Hi James, Worcester’s are usually great units. Personally, I don’t trust a boiler with a warranty lower than 5 years. I’m not sure if this answers your question or not. I would go for boiler cover, I guess, and if it breaks the cover will … cover it 🙂

  3. Quite interesting range of boilers but would be inclined to opt for highly rated Worcester or Viessmann Combi to replace my conventional boiler in a 2 bedroom flat.

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