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Which is the Best Combi Boiler? Pros, Cons and Costs

Best Combi Boiler
Looking for the best combi boiler? A combination boiler (known as a combi for short), needs to be reliable, efficient and have a long warranty. We are here to help, by not only highlighting the 5 best combi boilers, but also answering that all important question: how much does a combi boiler cost?

Year after year these boiler manufacturers are well reviewed by both homeowners and installers, thanks to providing the most reliable, energy efficient and high performance range of combi boilers available today.

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What is a combi boiler?

Combi boilers are the most commonly installed type of boiler in the UK for a number of reasons. While system and regular boilers require a hot water storage cylinder, a combi boiler is an all-in-one unit which will produce hot water for central heating and your taps. This saves a great deal of space in your home and often means it can be tucked away in a kitchen cupboard. With no water tank or cylinder needed it also results in a simpler and faster installation.

A combi boiler takes its water supply directly from the mains, heating it from the source, which usually results in a stronger pressure. This gives you the luxury of hot water on demand, so there's no need to worry about running out and having to wait for the tank to refill.

Best combi boilers

Choosing the best boiler replacement can be a confusing process at first, but with the right professional advice you needn't worry. While some larger or older homes may require a system or regular boiler because of a higher hot water demand or incompatible pipework/radiators, most homeowners will install a combi boiler.

But which are the best combi boilers on the market? We've put together this run down to point you in the right direction.

  1. Vaillant ecoTEC plus Combi
  2. Worcester Bosch Greenstar i Combi
  3. Baxi 800 Platinum+ Combi
  4. Viessmann B2KB Vitodens 200W
  5. Ideal Vogue Max Combi

Compare the best combi boilers in our Boiler Comparison Tool.

Vaillant ecoTEC plus Combi

Vaillant ecoTEC Plus Combi Boiler

The ecoTEC Plus is Vaillant's 'flagship' model and widely recommended by professional heating engineers. It is available in outputs of 25, 32, 35 or the largest 38 kW which is a great choice for larger homes with a high demand for hot water.

This boiler includes a 5 year warranty as standard with 7 or 10 years available when installed by a Vaillant accredited installer.

The ecoTEC Plus is also one of the more stylish models on the market with back lit digital display, contoured case and stainless-steel heat exchanger. The boiler has been awarded the Quiet Mark accreditation because of how quiet the boiler is when it is in operation.

Key Vaillant ecoTEC Plus features:

  • Rapid hot water delivery in just 5 seconds
  • Wide modulation range of up to 1:6 results improves energy efficiency
  • Flame lift detection system enables quieter combustion
  • Stylish contoured case design
  • Two-stage frost protection built in
  • Quiet Mark accreditation
  • Designed for quick installation
  • Compatible with aroTHERM air to water heat pump hybrid system
  • LPG convertible (Liquefied Petroleum Gas)
  • Available with a range of controls including wired, wireless and smart (vSmart by Vaillant)

The ecoTEC plus includes smart technology enabling it to drop to just 16% of its power when you don't need much heating, so you can save money and reduce emissions.

Worcester Bosch Greenstar i Combi

Worcester Bosch Greenstar i Combi Boiler
According to Worcester Bosch, this is their most popular combi boiler. It has been awarded a Which? Best Buy Award for 7 years running and regularly tops both homeowner and installer polls for reliability and performance. In addition, the brand currently holds the Royal Warrant to supply heating to the Royal Family.

Worcester Bosch Greenstar i features & benefits:

  • Simple boiler controls with clear information display
  • Zero risk of condensate pipe freezing in severe weather (resilient to freezing up to -15C)
  • Wide choice of controls including mechanical, digital and smart (Wave by Worcester Bosch)
  • Compact design for kitchen cupboard installation
  • Low energy pump reduces electrical usage
  • LPG convertible
  • Which? Best Buy Award for 7 years running
  • Achieves an A+ ErP package efficiency rating for heating when installed with a Wave smart internet connected control
  • Fills a standard kitchen sink in 45 seconds

The Greenstar i is ideally suited to small and medium sized homes looking for a low maintenance, low cost and reliable combi boiler.

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Baxi 800 Platinum Combi

Baxi 800 Platinum
Baxi have built a great reputation amongst boiler installers and homeowners and have been manufacturing since 1866. Baxi offers an extensive range of gas boilers that are innovative, efficient and durable.

The Baxi 800 Platinum range is available in outputs of 24, 28, 33 and 40 kW. The boiler delivers an impressive flow rate with the 40 kW delivering up to 16.4 litres of hot water per minute, which is perfect for homes with more than one bathroom.

Other key features and benefits include:

  • Rated ‘A’ for energy efficiency
  • Can be controlled using your smartphone or tablet
  • Optional built-in mechanical 24 hour timer
  • A low lift weight and compact size makes for a simple installation
  • Front access means easy maintenance and servicing saving you time and money
  • The Adey Micro2 Magnetic System filter offers long lasting protection
  • Available with an extensive 10 year warranty
  • Built-in frost thermostat

The Baxi 800 Platinum 40 kW is ideal for larger homes with more than one bathroom.

Viessmann B2KB Vitodens 200W

Viessmann B2KB Vitodens 200W

The Viessmann 200W is available in several outputs between 1.9 – 35 kW. Other key features and benefits include:

  • Rated ‘A’ for efficiency – up to 98% of the fuel used by the unit can be turned into heat
  • Very quiet in operation
  • The stainless steel Inox-Radial heat exchanger increases efficiency and reliability
  • Long life thanks to the MatriX-Plus burner with stainless steel MatriX surface
  • 7-inch colour touchscreen
  • You can control your boiler by connecting it to the WiFi and controlling it from your smartphone or tablet using the ViCare app
  • Includes a 3 year warranty as standard which extends to 5 year warranty if installed by a Viessmann accredited installer with the option to extend to 10 years
  • Compact wall-mounted boiler
  • Low fan speed results in quiet operation

The digital Viessmann 200W is rated ‘A’ for efficiency – up to 98% of fuel used by the unit can be turned into heat – saving the homeowner money and keeping emissions to a minimum.

Ideal Vogue Max Combi

Ideal Vogue Max

Ideal has been designing high quality boilers in the UK for over 100 years and is well known in the industry for producing great boilers at more affordable prices than other manufacturers. Ideal offers real value for money when compared to some other brands and is a popular choice for many homeowners and installers.

The Vogue Max Combi boiler is a relatively recent addition to the manufacturer's range and is regarded as their premium boiler. It is available in outputs of 26, 32 or 40 kW. This boiler includes a 10 year standard warranty straight out of the box, but this is increased to 12 years when the boiler is installed by an Ideal "Max" accredited installer.

  • 10 or 12 year warranty
  • Easy to read pressure gauge
  • Compatible with range of Ideal controls
  • Full text support for fault modes
  • Premium product using best components available
  • Compact unit with low lift weight enables quick installation
  • Service timer with telephone number display / service display to remind you when the annual service is due
  • Features a stylish composite design with damped opening control cover and large rotary control dials
  • Simple customer user interface; 3.5in full colour large backlit LCD display with plain text and graphics

In addition to a high quality boiler with a 12 year warranty, Ideal offers real value for money when compared to some other brands.

How much does a combi boiler cost?

When it comes to combi boiler prices, the first thing to consider is that you will get different prices depending on the installer you choose. Having said that, there is also a difference between brands as some are more costly than others.

We can't provide quotes or guarantees about how much a boiler is likely to cost you, but we can give you some estimates based on research.

Of the combi boilers we have looked at in this article, the Viessmann Vitodens is generally the most expensive on the market, while the Ideal Vogue Max is the least expensive.

Combi Boiler Model Typical Price (excluding installation)
Vaillant ecoTEC plus Combi £1,100 – £1,500
Worcester Bosch Greenstar i Combi £900 – £1,200
Baxi 800 Platinum+ Combi £1,200 – £1,500
Viessmann B2KB Vitodens 200W £1,400 – £1,700
Ideal Vogue Max Combi £800 – £1,100

Combi boiler installation costs

Once you've found the right combi boiler for your home, you'll need to hire a Gas Safe registered engineer to carry out the installation, which will add to the upfront cost of the unit itself.

The simplest, and likely to be the cheapest, combi installation is a like-for-like replacement, in other words, replacing an old combi boiler with a new one in the exact same location. Typically, this type of installation will cost somewhere between £1,000 to £1,500 depending on the property. This cost may also include in a system powerflush, which clears any debris, rust and sludge from the heating system to help it run more efficiently.

A more complex combi installation, which could involve replacing a different type of boiler (regular or system) or having the combi installed in a new location, would end up costing you more. In some of the most extreme cases, the total cost of having a new boiler installed could reach £2,500.

Combi Boiler Model Typical Price (excluding installation) Approximate cost of boiler fully installed
Vaillant ecoTEC plus Combi £1,100 – £1,500 £1,600 – £2,200
Worcester Bosch Greenstar i Combi £900 – £1,200 £1,400 – £1,900
Baxi 800 Platinum+ Combi £1,200 – £1,500 £1,700 – £2,200
Viessmann B2KB Vitodens 200W £1,400 – £1,700 £1,100 – £1,500
Ideal Vogue Max Combi £800 – £1,100 £1,300 – £1,800

Find out how much your new combi boiler could cost with our Boiler Calculator.

Best oil combi boilers

While most homes in the UK use gas combi boilers, there are some homes which are not connected to the gas grid. For these homes, oil combi boilers or LPG (liquid petroleum gas) combi boilers may be the best option. With oil and LPG boilers, you need to keep fuel on your property in a safe storage container and have your fuel delivered on a regular basis.

Of the gas combi boilers we have included in this article, the following are compatible with LPG:

  • Worcester Bosch Greenstar i
  • Viessmann B2KB Vitodens 200W
  • Vaillant ecoTEC plus Combi
  • Ideal Vogue Max Combi

If you are looking for an oil fired combi boiler, here are 3 of the best oil combi boilers on the market as well as average costs.

Combi Boiler Model Available Outputs (kW) Approximate cost of boiler (excluding installation)
Worcester Bosch Greenstar Heatslave II 18, 25, 32 £2,000 – £2,400
Grant Vortex Blue Internal 15-21, 21-26, 26-36 £1,500 – £2,500
Warmflow Kabin-Pak Combi 21, 26, 33 £1,900 – £2,200

Which size combi boiler do you need?

When we talk about boiler size, we mean it’s output in KW, rather than it’s dimensions. Combi boilers are available in a range of outputs to suit homes of most sizes from 1 bedroom flats to 4 bedroom houses and it's vital that you get a boiler with the right output installed for your home. A combi that's too small won't be able to meet your heating and hot water requirements, while a combi that's too powerful will end up increasing your energy bills.

However, if you have plans to expand your home, e.g. you're adding a conservatory, converting a loft space and/or adding more inhabitants, you may want to get a bigger boiler to ensure it meets your long term needs.

Combi boiler are rated by their heating output, kilowatt (kw) rating will usually be determined by how many radiators a property has and then assigning 2kw per radiator. For example, a house with 10 radiators only needs a 24kw combi boiler, however the lower the kw the less litres it can heat per minute. In some cases therefore, a higher wattage may be requested if high usage and flow rate is a concern to the home owner.

Generally speaking, the more bathrooms you have, the higher the output your boiler needs to be. A professional installer will be able to recommend the best combi boiler for your home but to help you narrow down your search, we've put together some guidelines based on industry recommendations:

Bedrooms Bathrooms Radiators Recommended Output
1 – 2 1 Up to 10 24 – 27kW
2 – 3 2-3 Up to 15 28 – 34kW
4+ 3+ Up to 20 35 – 42kW

A customer in a property with 5 radiators requested a 36kw boiler as he wanted the flow rate to be the best it could be. Every installation is unique.

Gas Safe Registered Engineer

For larger properties with more than 2 bathrooms, lots of inhabitants or a particularly high need for hot water, a combi boiler is not recommended. For a property with multiple bathrooms, the best option is always going to be a system or regular boiler. This is because a combi boiler takes its water supply directly from the mains and heats on demand. If multiple outlets require hot water at the same time, the combi boiler may struggle to maintain a consistent supply. A system or regular boiler however, include a hot water cylinder that stores a higher volume of hot water to meet this increased demand.

To help in your search for the best combi boiler for your home, you can compare combi boilers with different outputs in these guides:

Benefits of a combi boiler

Combi boilers are the most commonly installed boiler type in the UK. When you turn on the heating or a tap, the combi boiler responds within seconds and the all-in-one units means it’s compact enough to be installed quickly and more discreetly than it’s counterparts.

No matter which brand or size of boiler you choose, there are a number of benefits to having a modern combi.

High levels of efficiency

All combi boilers installed in UK homes have to meet efficiency levels of approximately 92%, meaning that combi boilers achieve incredibly high levels of efficiency which will help to lower your carbon footprint and reduce your energy usage.

Can help to lower your energy bills

Thanks to their high energy efficiency, these boilers will also save you money on your bills. At approximately 92% efficiency, a combi will only lose 8% of the fuel it uses, meaning that for every £1 you’re spending, only 8p is wasted.

So if you’re planning to replace your current boiler with a modern combi boiler, then you could potentially be saving £300 a year on your energy bills.

Space saving thanks to their compact size

There are 3 different types of boiler: combi, regular (traditional or heat-only) and system.

Out of these, combi boilers are the only type that don’t need water tanks or storage cylinders. This is because everything it needs to heat your home and hot water is wrapped up into a single compact unit.

Hot water to taps on demand

Rather than the hot water being stored in a hot water cylinder, like with regular and system boilers, combi boilers take water straight from the mains and heat it on demand. Not only does this get you quicker access to hot water but stronger water pressure too.

Easy to install

With everything being inside a single unit, combi boilers are the easiest type of boiler to install, especially when replacing an old combi boiler with a new one. This will help to save you time and money when it comes to the installation.

Quiet as they heat the home

The quietest combi boilers heat the home at a noise level similar to modest rainfall. Find the Quietest Combi Boiler.

Find the best combi boiler installers

While the price of installation will vary, you can really help yourself by comparing quotes from multiple combi boiler installers – and that's where we can help.

Complete our simple online form to let us know the type of work you need, which shouldn't take long at all, and we'll match your needs with fully-qualified Gas Safe engineers in your local area. You'll soon be contacted by up to 3 heating engineers who will all provide a free quote, leaving you free to compare them. That way, you can choose the quote that's best for you and make the best possible start with your combi boiler installation.


About the author


Adam is our resident home heating expert. His experience and advice has helped millions of customers improve the efficiency of their homes and save money.

approved by engineer This article has been checked and approved by a Gas Safe registered engineer.

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