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Last Updated on May 1, 2023

Combi Boiler Makes

Fortunately in the UK we’re spoiled for choices with several combi boiler makes available, even though many of the combi boiler makes may not actually be British.

Why Buy Combi Boilers?

combi boiler makes

Combi boilers are increasingly becoming the boilers of choice in the UK because of the reasons listed below:

They’re more efficient: Because combi boilers give you hot water on-demand, they don’t require cylinders to store hot water, and heat and reheat that water, saving you money on energy bills in the long run.  If your existing boiler is a non-condensing Open Vent boiler (also called regular or conventional boiler with attic tanks and hot water cylinder), or a system boiler (with a hot water cylinder), simply switching to the most efficient modern condensing combi boiler makes, you can save between £300 to £500 per year on your energy bills according to the Energy Saving Trust.

They Save Space:  Because you don’t need attic water storage tanks or hot water cylinders, you have extra space in your home.

They give you Safe, Clean Water: The drinking cold water you get through a combi boiler is safe to drink because it comes directly from the mains.  Whereas Open Vent boilers store cold water in attic tanks, which may not be ideal for drinking.

They are cheaper: Because you pay for only the boiler, and not for the attic tanks or cylinders or their installation, combi boiler installations are fairly cheaper.  The replacement parts are also easier to source and are readily available.

They’re Easier to Service and Repair:  With growing popularity, and wide availability, more trained engineers are available to repair and service most of the combi boiler makes.

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Best Combi Boiler Makes 2023

The UK market is much more price-sensitive compared to the European market.  For example, the German brand Viessmann, which is a world leader in commercial boilers, and is Germany and Europe’s number 1 boiler brand; makes one of the highest efficiency (98%) and most powerful boilers available in the UK, the Vitodens 200-W.  Which is their highest selling boiler in Germany, whereas their more affordable models Vitodens 050-W and Vitodens 100-W are what outsell the 200-W in the UK.  This also means that often times consumers in the UK buy cheaper combi boiler makes just to keep the initial costs down, but end up paying more over the years by paying more on energy bills due to a low-efficiency boiler or frequent repairs due to boiler breakdown.

We’ve ranked the best combi boiler makes available in the UK in 2023 based on combi boiler efficiency, features reliability, durability, price, uniqueness and technological prowess.

1. Viessmann

One of the leading international manufacturers of heating, industrial, and refrigeration systems, the Viessmann Group has:

  • 12,000 Employees Worldwide
  • 23 Production Companies in 12 Countries
  • Distribution Companies and Representative Offices in 74 Countries
  • 120 Sales Offices Throughout the World
  • Turnover of €2.37 billion

Their high efficiency, technologically superior boilers have been awarded the UK Best Buy status for the second year running in 2023.  Before entering the UK domestic boiler market, Viessmann has been the world leaders in the commercial boiler space for several decades.  Their transition into the domestic boiler market has been fairly recent, but that means great things for you as consumers.  Commercial boilers are larger, much more powerful and technologically advanced because they’re supposed to efficiently heat massive factories, stadiums and large buildings.  This means Viessmann’s commercial heating experience and know-how translates well into the much smaller domestic combi boiler in your home.

If Viessmann boilers are so good, how come they can compete on price?

Their large factories around the world allow them to manufacture internal components in-house, which helps them compete on the same price point as even the less technologically advanced combi boiler makes in the UK.  Many of their rival manufacturers source their internal components from third-party manufacturers.

By manufacturing components in-house, Viessmann also has control over patented designs like the Inox-Radial Stainless Steel Heat Exchanger (pictured below):

condensing or combi boiler, viessmann heat exchanger

So, why is the heat exchanger better than Worcester Bosch’s?

The primary heat exchanger to a boiler is what an engine is to a car.  So, the more efficient and durable the engine is, the better the car performs.  Viessmann has patented the Inox-Radial Stainless Steel design, unique to their range of boilers.  Stainless steel offers much more durability, resistance to corrosion, oxidation and seizing.  No doubt it is a superior metal compared to aluminium (used by Worcester Bosch).  Pretty much all the rest of Viessmann’s rival combi boiler makes in the UK source their aluminium heat exchangers from a third-party manufacturer based in France.  The graph below shows a direct comparison of both heat exchangers for durability and efficiency through laboratory tests done under the same parameters, and what it means for your combi boiler:

condensing or combi boiler

The aluminium heat exchanger drops off dramatically over time.  So, a Viessmann boiler with a stainless steel heat exchanger will maintain the same efficiency for much longer, simply by being durable and resistant to corrosion.  And because the main internal component is so tough, it will break down less often too.  In monetary terms, the ROI (return on investment) over years is much better with a Viessmann boiler compared to other brands.  Another brand with an aluminium heat exchanger will be ready to be replaced in half that time.

  • 94% to 98% Energy Efficiency
  • Class A rated
  • Patented Stainless Steel Inox-Radial Heat Exchanger (Manufactured in-house)
  • 10 Years Extended Warranties on Boiler + Heat Exchanger
  • Combined PRV (Pressure Relief Valve) and Condensate Combined
  • In-Built Shock Arrester
  • One of the quietest boilers on the market
  • Available in outputs from 4.7 to 35 kW
  • Low CO2 emissions for reduced environmental impact
  • User-friendly Backlit LCD Touch screen for easy operation

FAQ on Viessmann & Answers:

1) I heard sourcing Viessmann spare parts is difficult in the UK. Is that right?

Answer: No. That is outdated information.  There may have been some truth to that when Viessmann first started in the UK.  But since then, they’ve opened their UK headquarters in Telford, Shropshire, and all Viessmann spare parts are stocked at Plumbases and several other plumbing merchant locations around the UK.

2) Brexit is coming, and Viessmann is German. What if my boiler no longer gets support and service?

Answer: As we mentioned above, Viessmann’s UK headquarters are in Telford.  Even if Brexit goes through, they will continue to function the same way as they are now, because they have invested extensively in the UK.  There are very few British boiler manufacturers left.  Worcester “Bosch” is wholly German-owned, so is Vaillant.  Baxi is owned by BDR Thermea, a Dutch company.

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2. Worcester Bosch

Worcester Engineering was founded in 1962 and then acquired by Bosch, a German company in 1992.  Worcester Bosch has been one of the market-leading combi boiler makes in the UK for a long time now.  Known for manufacturing high quality, efficient, reliable and durable boilers which have been the boiler of choice for UK consumers for decades now.

combi boiler makes, worcester bosch

Whether you buy a Worcester Bosch or Viessmann, you cannot go wrong either way.  Viessmann’s stainless steel heat exchanger is the only reason Worcester Bosch is second on this list.  They have an extensive boiler range whatever your property size may be.  The only type they don’t seem to have are storage combi boilers suitable for larger properties.  They have the floor-standing Greenstar Highflow series for that though, which may or may not be better than a storage combi boiler.  Because of their history, it seems like Worcester Bosch has been present in the UK forever.  And they have maintained their place in the top 3 always when it comes to best combi boiler makes in this country.  The term “Worcester Boiler” has been synonymous with central heating for generations.  Lately, though we do feel they’re lagging behind some of their rivals in terms of technology.  Maybe because they’re market leaders and don’t feel pushed to innovate.  There is no way the aluminium heat exchangers inside these can compete with the stainless steel ones from Viessmann over years.  In any case, you still get your money’s worth when you buy a Worcester Bosch boiler.

  • High hot water flow rates
  • Simple boiler control knobs with clear temperature display
  • Low energy pump reduces electrical usage
  • Frost protection is included, reducing frost risk if installed in a garage or a loft
  • Inbuilt keyless filling link making it easy to refill your system
  • Large Condensesure style siphon built into the boiler – eliminates frost risk
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3. Vaillant

combi boiler makes, Vaillant

Present in over 20 countries, this is another German company that is truly international.  Like Viessmann, Vaillant works on improving on already existing innovative technology , which is why they too have used stainless steel heat exchangers in some of their premium boilers.  Honestly, the top 3 positions in this list can be interchangeable at times, and Vaillant have been able to maintain their top 3 position in UK’s premier combi boiler makes in the last two decades.

  • Four combination models covering 25, 32, 35 or 38kW heating outputs
  • A flow rate of up to 15.9 litres per min for fast hot water*
  • ErP A rated for both hot water and heating efficiency
  • Dimensions in mm (825 model): H 720 x W 440 x D 338
  • Works with LPG where required
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4. Ideal

combi boiler makes, Ideal boilers

Ideal Boilers have been active since 1906, and in the last 112 years they’ve had their ups and downs, but they have maintained their position in the top 5 combi boiler makes in the UK.  People have complained about Ideal boilers in the past, but the company has worked hard to overcome any deficits.  Their latest range of combi boilers are the best they’ve ever been.  From stainless steel heat exchangers on their flagship boiler to 12 years warranty, they are definitely inching towards the top.

  • Manufactured in the UK
  • Quiet Mark
  • Queen’s Award 2013
  • Compact Dimensions
  • Good Housekeeping 2013 and 2017
  • Built-in frost protection
  • Energy Saving Trust endorsed
  • LPG conversion available for 30kW
  • Easy to use fully backlit LCD display
  • 7-year warranty & 10-year warranty on heat exchanger
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5. Baxi

combi boiler makes, baxi

Baxi has been manufacturing in the UK since the 1860s, and are now part of the Netherlands based BDR Thermea Group.  Much like Ideal, they have had their ups and downs.  During the back boiler era, the Baxi Bermuda was a favourite in the UK.  Since then they’ve never really cracked the top echelons of best combi boiler makes, but nonetheless, they fit the gap between premium and affordable quite well.

  • Instant hot water
  • 7-year warranty
  • Energy Saving Trust Endorsed
  • Cupboard fit
  • Easy to use controls
  • Meets minimum energy efficiency rating required for Boiler Plus compliance
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Other Notable Combi Boiler Makes


One of the premier Dutch combi boiler makes, but lesser-known in the UK compared to the top 5 in this post.  Now, because their presence and sales in the UK is too small to measure against other manufacturers, don’t let that deter you from the fact that they manufacture some of the highest efficiency combi boilers available in the UK, and in fact all over Europe.  Their stainless steel heat exchanger labeled iCon is unique, and the company claims it retains 98% efficiency over many years.

7. Grant UK

Grant are at the top of the list of oil combi boiler makes.  Since we’re talking primarily about gas boilers in this post, we haven’t included them in the top 5.  But they make high quality, high-efficiency oil combi boilers, no doubt about that.  And this isn’t just opinion, but a fact, as they have been awarded the UK Best Buy Oil Boiler award for many years in a row now.

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