Review: The Best Combi Boiler in the UK 2021

Table of Contents

To really find the best combi boiler we had to go through numerous posts, speak to engineers and open up warranties and guarantees to dig into the small print. We found what makes a great boiler isn’t always the brand on the front but instead the parts. 

There are also costs to consider, money talks so the purchase and fitting price must be taken into account along with any service costs and the price of parts. 

We’ve been online a whopping 17 years – long before TrustPilot or other review sites and people talk, good and bad, but all of these factors combined gave us a clear pecking order with a crystal clear winner

We actually found out more from engineers about what not to buy than what to buy, for the simple reason that engineers fix boilers that have broken. We don’t want boilers to break. Same as the AA or RAC, ask them which cars they fix the most at the side of the road and those are the cars to avoid buying. Boilers are no different.

Short on Time – Here’s the Bottom Line:

What are the Best Small to Medium Combi Boilers?

#1. Worcester Greenstar 25i

#2. Viessmann Vitoden 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

 

And now for a slight curve ball but pay attention if you live in a particularly large property as these are the outright winners:

Best Most Powerful Combi Boilers:

#1. Worcester Greenstar 42CDI

#2. Viessmann Vitodens 111-W 35kW

#3. Ideal Boilers Vogue C40 Gen2

Best Combi Boilers: Review Criteria

Combi Boiler Warranty [Part 1]

The big thing you need to focus on, that should be top of your list, as it was ours is: Warranty

‘‘A boiler is only as good as its warranty.’’

But; and it’s a BIG but – boiler warranties aren’t always simple, so it’s also a case of how you are able to get that warranty. And then secondly how to maintain that warranty.

I’ve put together a warranty guide further down below and we review and then rate the leading brands like Worcester, Viessmann, Baxi, Ideal etc by their warranty.

[We’ve done this because most of the time people choose a boiler based on the ‘headline warranty’ from a manufacturer such as ‘comes with a 7 year warranty’. They don’t realise there can be hoops to jump through to get that warranty. So that’s why we have cost all this in]

Combi Boiler Warranty [Part 2]

The boiler with the biggest warranty should really top the bill and to cut to the chase thats Worcester Bosch. They are literally unbeatable! They have 10+ years with nearly all of their boilers, plus they have guarantees on some of their parts which most other manufacturers don’t have. The trouble with Worcester was that they were expensive – but that was 20 years ago!

Now they really aren’t, IF you use online boiler comparison sites like Heatable which provide quotes on screen in under 2 mins, plus they run through all the questions about your home and best boiler for you and all you have to do is click some buttons. 

But why we really like them is their transparency. They don’t list all the boilers they make the most amount of money on at the top, they give you the cheapest first. Try it out here for yourself, you don’t need to input any personal details either and they can fit them NEXT DAY.

I just did it now and this is what’s recommended for me:

Best Combi Boiler Brand

Well we’ve already mentioned the warranty and what you want is 7+ years. At a minimum you require a 5 year warranty but no lower than that.

So ‘brand wise’ a huge emphasis should be on the warranty but after that warranty expires – then what?

Well this is where clear brand leaders start to emerge, the sorts of brands where the boilers are as tough as ox’s, that seem to go on forever and forever.

In the UK we actually have a fair few boiler brands, but not all are worth a mention. I’ll keep it short and only list the very best. 

Here’s the top 5 best boiler brands in the UK:

#1. Worcester Bosch Combi Boilers

By far the best known brand of boilers in the UK, Worcestershire Bosch are the Rolls Royce of boilers. Be honest they were probably the brand you were thinking would be in first place. The story with them is that ‘Worcester’ were making excellent boilers and Bosch came along with all their German efficiencies, merged and made an excellent boiler even better.

Why are they so good?

They are super reliable, highly highly efficient and recommended by most boiler installers. The added bonus is they have warranties of up to 12 years on some products but their bog standard warranty is a whopping 10 years! 

As we have said before the let down used to be the price, 20 years ago they were the high end of the price spectrum. But even then you got what you paid for and they were still worth it even then.

Where they really cracked the market was a simple piece of business genius called vertical integration. They now work directly with some online installers, that’s helped improve the number of installs per year and that’s meant they now manufacture at a larger volume which has brought the price down – right down! 

You can now get a fixed price for a Worcester Bosch boiler fitted the next day, from Heatable using this simple onscreen form. No names or personal details required, just a pretty knock out price. Try it yourself here.

2. Viessmann Combi Boilers

German built and they do deliver on that expected robustness and reliability. They are ‘A Rated’ boilers which have the best efficiencies and this isn’t waffle either and ‘A Rated’ boiler according to the Energy Saving Trust will save you £155 per year in bills [if you previously had a F rated boiler]. 

So how do Viessmann do it?

Simply in terms of volume – they are Europe’s largest manufacturer of boilers – so that’s how they do it, they literally make a huge number of boilers. They’ve broken into the UK market by offering their premium boilers at very respectable prices and have rapidly been gaining a larger share of the market. 

3. Ideal Combi Boilers

We mentioned Ideal above already. They got 3rd place in our lists or a silver medal, so this brand deserves respect.

Price is the issue however – not that they are necessarily more expensive than other brands but for around the same money, when using an online boiler installation company, as a Worcester Bosch. 

For comparison the Ideal Logic Plus boiler has a 7 year warranty and is very well respected amongst installers but are actually comparable to the Worcester 25i or 30i in terms of price. So when you add in the fact Worcestershire have an extra 3 years warranty on their boilers vs Ideal’s 7, Ideal can get overlooked. 

4. Vaillant Combi Boilers

Really awesome looking boilers, with digital display screen and trendy designs. But boilers live in cupboards so discount my last point as looks are irrelevant here. 

Not just trendy looking, these boilers are manufactured with longevity in mind as they have rigorous build standards that should not be sniffed at.  

5. Baxi Combi Boilers

The best entry level boiler on this list. Probably not as well known as the brands higher up the list but this British brand is climbing the ranks. 

Baxi’s offers their Baxi 600 and Duo-Tec boiler as a direct match to Ideals Logic Plus. And they also match Ideals 7 year warranty with a 7 year warranty of their own. 

They even offer boilers with longer warranties than 7 years to try and match the likes of Worcester Bosch. Baxi’s Premium, Premium+ & EcoBlue Advance comes with a 10 year warranty – watch out Worcester.  

They also offer a range of boilers that are very very entry level with their Baxi 100, 200 & 400 range. But it’s probably best to stay away from any boiler with anything less than a 7 year warranty.

Combi Boiler Sizing

Best combi boiler for 1-2 bed properties

Worcestershire Bosch | Greenstar 25i | 5-8 Year Warranty | Price [installed]: from £1,795* 

Worcestershire Bosch | 28, 32 & 36 CDI | 5-10 Year Warranty | Price [installed]: from £2,195*

Viessmann | Vitodens 050-W 29kW | 10 Year Warranty | Price [installed]: from £1,845*

Ideal Boilers | Logic+ 24 | 7 Year Warranty | Price [installed]: £1,750

Ideal Boilers | Vogue 26 | upto a 10 Year Warranty | Price [installed]: £1,990

Ideal Boilers | I-Mini 24kW | 2 Year Warranty | Price [installed]: £1,650

Baxi | Duo-tec 24 | 7 Year Warranty | Price [installed]: £1,700

Best combi boiler for 3-4 bed properties

Worcestershire Bosch | Greenstar 30i | 5-10 Year Warranty | Price [installed]: from £1,970* 

Worcestershire Bosch | Greenstar 34CDI | 5-10 Year Warranty | Price [installed]: from £2,100*

Viessmann | Vitodens 050-W 35kW | 10 Year Warranty | Price [installed]: from £1,970*

Viessmann | Vitodens 100-W 30kW | 10 Year Warranty | Price [installed]: from £2,395*

Ideal Boilers | Logic+ 30 | 7 Year Warranty | Price [installed]: £1,935*

Ideal Boilers | Vogue 32 | upto a 10 Year Warranty | Price [installed]: £2,200

Baxi | Duo-tec 28 | 7 Year Warranty | Price [installed]: £1,900

Best combi boiler for 4-5 bed properties

Worcestershire Bosch | Greenstar 42CDI | 5-10 Year Warranty | Price [installed]: from £2,750* 

Viessmann | Vitodens 050-W 35kW | 10 Year Warranty | Price [installed]: from £2,080* 

Ideal Boilers | Logic+ 35kW | 10 Year Warranty | Price [installed]: from £2,110* 

*prices available from HEATABLE

You can now see how much cheaper it is to use one of the UK’s largest online boiler installers – Heatable. The prices are so competitive because they do the volume, it’s as simple as that.

What is the best combi boiler?

#1 Worcester Greenstar I Combi Boilers

Nearly every engineers ‘go to boiler’ is a Worcester Bosch. It’s probably the one brand you have heard of too because it’s now ‘the’ household brand name. 

But why are Worcestershire Bosch boilers top of this list and why should you buy one?

Efficiency 

They haven’t earned the respect of millions of homeowners and installers for nothing. Their 25i and 30i combi boilers are the most popular from their range and that’s for a reason. 

Firstly they are about 87.7% efficient when they are running flat out, so, say, in the morning when the central heating kicks in and everyone makes a dash for the shower you are still getting incredible efficiency.  

But these little beauties when running at around 30% capacity will work at a circa 99.4% efficiency, which is incredible. 

Plus if you currently have an old boiler to compare these efficiencies to, in terms of savings in energy bills in real terms is about £155 per year. 

So what we mean by that is by swapping out an old F rated boiler and replacing it with a new ‘A Rated’ Worcester Bosch that will save you £155 per year in bills. 

So if you apply that saving over 15 years – bingo. If you got one installed with an online installation company like Heatable the saving in energy bills alone would pay for the boiler itself! 

Worcester Bosch Installation  

Installation costs are no way near as bad as they once were. Sure if you decide to use a local installer who goes down to the plumber merchant or Travis Perkins, buys the boiler and charges you to install it, well that scenario you’re probably looking at around £2,200. Then you have to add the VAT on that at 20%.

Or compare that price to a national installer like the ones you see on the TV, running ads all day for brand awareness and they have to make that outlay back somehow and it’s through the higher prices they have to charge for installations. 

BUT compare all that to the new breed of ‘online boiler installation companies’ companies like HEATABLE where you can get a 25i fitted [next day!] for under £2,000 it should start to make sense.

Don’t believe me look at the quote we just got for a new Worcester boiler, fully installed with a 10 year warranty:

It took 90 seconds with no personal details required or any messing around. Try it here yourself

Worcesters Whopping Warranty

On Worcester’s Greenstar I range you get upto 10 years warranty. That should be reason enough to choose Worcester, as there aren’t many manufacturers that offer that. And none offer that with the same pedigree as Worcester Bosch.

The best combi boilers have the longest warranties and it’s not hard to work out why. Think of it in reverse, why would anyone provide a warranty on something they thought would break? They wouldn’t, is the answer as that is daft. 

A long warranty is the manufacturers way of expressing their view that they stand behind their product. And let’s say they get it wrong and something breaks under warranty, what happens?

If something breaks on your new boiler whilst it is still under warranty, it will be repaired and you don’t have to pay a penny, it’s as simple as that. 

Compare that to say a 5 year warranty – the manufacturer is literally telling you that the parts they use dont have the same longevity as another boiler manufacturer that offers a 10 year warranty. 

Whilst on the whole boilers with 5 years warranties are cheaper to purchase then the factor any call out, parts and repair costs after those 5 years – it’s no longer cheaper. 

So get something better in the first place to save the hassle. Heatable the online boiler installer now offers finance for new purchases so that’s another big tick in their box.

Worcesters in Winter 

It will surprise no one to say the majority of breaks, repairs and replacements of old boilers come in winter. 

The most common boiler issue in winter is a freeing condensate pipe. This issue reeks havoc every year and still people have no knowledge of what’s causing the issue and subsequently why their boiler wont turn on. 

Worcester’s answer was simple: ‘Condensure’. This will protect your boiler down to -15C so you have one thing less to worry about at home. 

Worcester Bosch Drawback

Size: it’s not a huge deal but size is definitely worth mentioning.

There is no issue with the Worcester Greenstar I if you are not planning on moving your boiler when you install that lovely shiny new one. 

For instance if you have it ‘wall hung’ or tucked neatly away, in say, the airing cupboard you will have no problems with the Greenstar I. 

But if you want to put it in a kitchen cupboard…well you can’t – they are too big. 

So instead the right boiler for you is the Worcester SI Compact, same great Worcester brand and warranty but only smaller in size. 

Is the Worcester Greenstar combi Boiler the right one for you?

Absolutely but which exact model? Well that depends on your home. For instance you could have more radiators a longer heating run or better than average insulation. It is not a one size fits all kind of thing.

But don’t despair, the solution is super simple. If you have a spare 90 seconds now jump over to HEATABLE and fill out this multi choice questionnaire with just a few clicks. They will give you the choice of the absolute best boiler for your home, for a fixed price.

You wont need to put any personal details in, it gives you an answer on screen here and now, they offer finance if required and they can fit a new boiler the very next day! What’s not to like?

Ok so we have covered the creme de la creme of boilers – Worcester Bosch, but who made second place?

#2 – Viessmann Vitodens Combi Boiler

Viessmann are now Europe’s largest boiler manufacturer but volume doesn’t mean anything if they are producing rubbish. Well they aren’t, you’ll be glad to hear they make truly superb boilers and are well worthy of the second spot.

Most noted are these two models, the Vitodens 050-W that comes in both 29kW & 35kW and the Vitodens 100-W which has alot more power than the 050-W. 

Efficiency

Vitodens are ‘A Rated’ – well being German you’d expect nothing less. That means saving on bills and the planet. 

If you replace your old F rated boiler with a new Vitoden ‘A Rated’ boiler you could save around £155 per year. Now if that wasn’t reason enough then Vitodens low CO2 emission will have you jumping for joy. 

Installation Costs

The Viessmann Vitodens 050-W 29kW comes in at £1,845 inc VAT and inc fitting. That’s a fixed price only available from HEATABLE. Finance, if required, is available and you’re really caught short you can order before 3pm and have it fitted the next day. You read that right – next day fitting. Infact the finance on this boiler only works out to under £25 per month. 

With that deal you also get free wireless heating controls, an Adey Sense filter which normally most other engineers charge more for and you also get a free system clean. That’s a super deal when you shop around and compare that to other premium combi-boilers. 

Viessmann Vitodens Warranty

Their boilers aren’t just efficient, they are also robust. In fact they are so robust Viessmanns carry a 10 year warranty, if fitted through HEATABLE which are a recommend and trusted installer. 10 years is as good as you are going to get…what more can I say.

Should you buy a Viessmans Vitoden boiler?

Based on everything above, absolutely. But you could need help choosing the exact model that will work perfectly in your home. Luckily this is done with just a few clicks of your mouse, you don’t need to provide any personal information and you fixed price will appear on screen ready for to buy and have have fitted tomorrow. 

#3 Baxi Duo-tec | Baxi EcoBlue Advance Combi Boiler 

Baxi, which is proudly built in the UK, makes third place on our list. Baxi is the budget friendly option but that doesn’t mean it is void of quality. 

Baxi offer two main boiler models the Duo-tec and the EcoBlue. 

The Duo-tec provides up to 40kW meaning you will achieve 16.4 litres of hot water per minute. The Duo-tec was designed with small to medium sized homes in mind.

The EcoBlue was designed for larger homes and is the more powerful model. With the EcoBlue you will get everything you get from the Duo-tec and more; whilst meeting the energy efficiency rating required to be compliant for ‘Boiler Plus’.

Efficiency

All Baxi models are ‘A Rated’ for both heating and water so again there are savings in your annual running costs and green is good for the environment. 

Baxi Installation Cost

£1,800 all in for the Baxi Duo-tec 28

#4 Ideal Vogue Combi Boilers

Ideal boilers don’t really have a significant USP but they are well respected having been around since day dot. The Vogue range is their top of the line, premium combi boiler, built with perfection in mind. 

Ideal has these great points:

  • Very quiet
  • Frost protection
  • 3.5″ LCD full colour display

 

Ideal Vogue Boiler Installation costs

The Vogue 26 comes in at around £2,000

The Vogue 32 is slightly more expensive at £2,200

Whilst their Vogue C40 Gen2 will set you back around £2,500

Efficiency 

As you would expect they are efficiency ‘A-Rated’ for both heating and running water and the Vogues are endorsed by the ‘Energy Saving Trust’. 

Vogue Combi Boiler Warranty

The Vogue range comes with a 10 year warranty, on parts and labour. Vogue have seriously upped their game in terms of warranties to compete with the likes of Worcester Bosch and Viessmann. 

The 10 year warranty does only apply if the boiler is installed with an Ideal system filter. 

Ideal Vogue Boiler: Should you get one?

They are a robust boiler, built to last with a long warranty, so yes they should be on your short list. 

But in the same category for price, efficiency ratings & warranty is the Worcester Bosch & the Viessmann and most installers and engineers would pick those two over an Ideal.

Warranty Guide: Combi Boilers

Warranties can get confusing, mixed up and muddled when comparing across brands. As previously mentioned installing a new boiler through an accredited network can validate or even prolong a warranty.

Some manufacturers do even charge for an additional warranty.

So the advice here is simple – check before buying. Boiler manufacturers know warranties make up, as we discussed above, a huge influencing factor when deciding which boiler to purchase and can run promotions with extended warranties. So again, before buying, just check the status.

Combi Boilers: The Small Print 

Warranties really are important and the things on this list are the some T&C’s that you could be required to meet. 

  • Installation has to be by a Gas Safe engineer
  • Annual servicing from a Gas Safe engineer
  • The boiler warranty must be registered within 30 days of installation.
  • Certain brands require the boiler to be installed by someone from their network to unlock any additional warranty. 

Very common items within T&C’s that can void warranties with manufacturers:

  1. Allowing ‘sludge’ to build up within the system – prevent this by having a magnetic system filter installed BUT also having it cleaned out with every service. 
  2. Limescale build up – [very common in hard water areas] prevent this by installing a Lime Scale Inhibitor

Worcester Bosch Combi Boiler Warranties

Worcester actually have up to a 12 year guarantee on some of their products if your boiler is installed by a ‘Worcester Accredited Installer’. Yes you read that right a whopping 12 year, no quibble guarantee. 

The vast majority of their boilers have a 10 year warranty which has pretty much become the industry benchmark now with other manufacturers trying to keep up as Worcester trail blazes ahead, but not all of their boiler have a 10 year warranty. 

Companies like HEATABLE offer 10 years on all their products as they have built up industry leading relationships over the years. 

Choosing Worcester Bosch would be a smart move, as with their CDI range you get up to 10 years.

But what most people don’t know is, choosing a gas safe engineer that’s accredited through the Worcester Bosch installer network can get you extra warranties!

Worcester Bosch small print can be found here for those who like us, really do like to read this stuff: https://www.worcester-bosch.co.uk/guarantee-terms-and-conditions.

Installation Details                   |    CDI Range      |     I Range       |       SI Range      |

Worcester Bosch Boiler Only            5 years                  5 years                5 years

 

Through Accredited Installer            7 years                  7 years                7 years

 

With Accredited Installer, Filter,    

& Controls                                           10 years                8 years                9 years

Ideal Combi Boilers Warranty

Ideal have kept it as simple as possible with their warranties. 

They do have an installer network but you can use any ‘Gas Safe’ engineer to install their boilers and still get the warranty. Gas Safe is the industry recognised safety standard. 

Boiler Model      |      Warranty

  Instinct                        2 years

  Logic                           2 years

  Logic Plus                   7 years

  Vogue                       10 years

Their full T&C’s can be found here: https://idealheating.com/uploads/documents/terms-and-conditions-of-ideal-guarantee.pdf

Baxi Combi Boiler Warranty

Boiler Model      |      Warranty

Duo-tec                        7 years

Platinum Combi        10 years

Baxi, like Ideal, do have their own network of approved installers. However in order to get the warranty you don’t necessarily have to use one. Instead you can use any Gas Safe engineer. 

Baxi Warranty can be found here: https://warranty.baxi.co.uk/terms