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Best condensing boiler

best condensing boiler

What is the best condensing boiler?

Have you heard the term ‘condensing’ and wondered how that relates to your new boiler and its energy efficiency?

Well, back in 2005, the UK Government passed legislation that said all future boiler installations needed to be for models that were condensing rather than non-condensing.

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That then means that all the boilers that are currently available, are condensing. And, that includes combi boilers, as well as gas and oil boilers. Now, with that information, you can see that just looking for a condensing boiler isn’t going to help you narrow down your choices for a new boiler!

It also means that there are dozens of boiler manufacturers to consider which can again make finding the right boiler even more challenging.

But, thankfully, that’s where we come in to make your life easier. That’s because, in this guide, we’re going to provide you with all the information you need to make a great choice to get your heating and hot water needs met with one of the best condensing boilers.

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The results for the best condensing boilers

We considered brand quality, energy efficiency, key features and warranty length of dozens of new boilers before coming up with our shortlist.

If you want to know right now which condensing boiler brands and models got onto our list of the best condensing boilers, well they are, in no particular order:

  1. Worcester Bosch 4000
  2. Viessmann Vitodens 050-W
  3. Worcester Bosch 2000
  4. Ideal Logic C30
  5. Worcester Bosch 8000

How does a condensing boiler work?

A condensing boiler is all about using the technology of condensing so that it can make better use of the generated heat. When the boiler is burning fuel such as gas or oil, it results in the production of hot gases which are then released into the air outside of your home via a flue.

The non-condensing boiler loses out on all the real potential of those hot waste flue gases as they disappear out into the environment.

Meanwhile, condensing boilers work by capturing those hot gases and then they force them back into the boiler’s system. They then get pushed through the larger heat exchanger and into the primary circuit

The primary circuit in condensing boilers then moves that recaptured heat to either the radiators via the heating circuit or through to the domestic hot water.

Condensing boilers vs non-condensing boilers

Condensing boilers achieve a level of efficiency that’s just not possible with non-condensing boilers. It’s not unusual for a new condensing boiler to achieve efficiency levels of over 90%. Meanwhile, the non-condensing boilers are considered energy efficient when they’re in the range of 70-80%.

This then means that with a condensing boiler installation, homeowners can save money through reduced energy use and that can amount to hundreds of pounds in lower heating bills every single year.

Condensing boilers are also a much greener option as they burn less fuel reducing carbon emissions while also preventing the release of flue gases into the environment.

Read more: Condensing boiler vs combi boiler

Are combi boilers the same thing as condensing boilers?

When you’re looking for a new boiler, you might see the term condensing boiler being used interchangeably with a combi boiler.

They are, however, different things. That’s because condensing is the technology that’s being used inside the combi boiler, but you also have a system and regular boilers that are also condensing.

A condensing combi boiler would probably be a better description. That all said, now that the modern condensing boiler is every single boiler that comes on to the market, it becomes a bit of a moot point to even use the term!

What are the advantages of a condensing boiler?

The key advantages of modern condensing boilers over non-condensing boilers are:

Reduced carbon emissions

Modern A-rated condensing boilers have a much lower carbon output than the old non-condensing boilers. In fact, by trading your old boiler in for a new boiler that makes use of the condensing technology then you could save over 1,000 kg of CO2 every year.

Much lower energy bills

According to the Energy Saving Trust replacing an older non-condensing boiler with a new boiler that’s A-rated condensing boiler, could result in your energy bills being £300 lower every single year.

If you then combine that with a smart thermostat you could save even more. It’s estimated that using a product like Nest or Tado, paired together with thermostatic radiator valves you could save even more.

We estimate that could be up to another £75 per year on your energy bills. This, over the years, can offset the new boiler cost incurred when you replaced your boiler.

We think you’ll agree with us that those make for pretty strong reasons as to why the legislation was passed and how condensing boilers result in huge benefits for homeowners.

Do I have a non-condensing boiler?

It’s might just about possible that you could move into a property that has a boiler that is non-condensing already fitted. But, as it would have to be installed prior to 2005, it’s going to be at least 16 years old.

That means even in terms of age, it’s going to have a vastly reduced efficiency level and is likely to need regular visits from engineers to keep it up and running. Then there are those huge advantages that a condensing boiler would give you.

If you find yourself in this situation, then it really is time to think about getting a new boiler quote and to start enjoying those much-reduced energy bills!

Boiler Plus regulations

Just while we’re talking about new boiler legislation, it’s also worth mentioning the Boiler Plus regulations that came into force in April 2018.

These required all new boilers installed in England, Wales and Scotland to achieve a minimum performance standard of 92% ErP and that they must also include one of the following technologies: 

  • Flue gas heat recovery systems
  • Weather compensation
  • Load compensation
  • Smart controls featuring automation and optimisation functions

With the manufacturers able to choose which of these features on their gas boilers it is worth checking out which gives you the most energy-efficient boilers and the greatest reductions in carbon emissions.

You’d think that these changes might make it easier to find the best gas boiler for your home but it can make things even more complicated.

That’s why we’ve made it easy for you to enter a few details about your home and heating requirements and we then provide personalised recommendations along with your new boiler quote.

Different boiler types

Before we provide you with all the details on the five best condensing boilers we’re just going to whizz through the different boiler types.

That’s because it’s important to understand which gas boiler you have right now and whether a new boiler of the same type is going to meet your needs in the future.

Combi boilers

The combi boiler is the most popular choice for new boilers in the UK. It has no need for a cold water tank or hot water cylinder as it takes the cold water supply directly from the mains and it delivers hot water on demand. That then means that it doesn’t need a cylinder to store the heated water.

That makes them a great choice for the central heating system apartments or homes where space is tight. It also makes for a very straightforward boiler installation and maintenance requirement.

Because combi boilers heat water on demand, you’ll never run out of hot water. On the downside though, they can struggle to meet the needs of busy households or where there is more than one bathroom.

If you have a larger home, do make sure that you look out for combi boilers with higher power output.

System boilers

System boilers pull the cold water from the mains supply but once it’s heated it’s then stored in a hot water cylinder ready to be used. That means that a system boiler can cope with heavier demands for hot water, where there’s more than one bathroom, for example.

One of the downsides of system boilers comes from the need to find space for the hot water cylinder. If your family use lots of hot water there is the possibility that you can run out of hot water.

Although system boilers are much more efficient thanks to the condensing technology, there is still the potential for them to lose heat and so have lower levels of energy efficiency while the hot water is being stored.

Heat only boilers

This type of heating system, which are also known as a conventional boiler, has not only a cylinder for the hot water but also a cold water tank. That can make them challenging to find room for. They do have pretty much all the same advantages and disadvantages of the system boiler apart from that need for the water tank.

While there is generally a move away from this boiler type and heating system, there can be times when it’s easier to replace like for like rather than swap out a heat-only boiler for a combi boiler or even a system boiler.

The best condensing boilers

So, here we go. Our top five picks for the best condensing boilers on the UK boiler market encompassed three condensing brands, Worcester Bosch, Viessmann and Ideal.

Worcester 4000

From the powerhouse that is Worcester Bosch, the Greenstar 4000 is their new condensing boiler.

Worcester Bosch is one of the best selling boiler brands in the UK. They have a strong reputation with both the installation engineers and customers and for the last ten years, they’ve been awarded Which? Best Buy Award.

The Worcester Bosch Greenstar 4000 series is designed to replace the Greenstar i, which has been one of the top-selling Worcester boilers.

Read more: Worcester 4000 review

Greenstar models

The Greenstar 4000 is available as both a system and as a combi boiler and it runs on both natural gas and, if you’re not on the mains gas grid, then it can also run on LPG.

Greenstar combi boiler

The condensing combi boiler is available in two different power outputs, so that’s 25kW and 30kW. That makes it suitable for most small to medium family homes with a single bathroom.

Greenstar system boiler

The system version of the Greenstar is available in five different power outputs, 12kW, 15kW, 18kW, 21kW and 24kW.

If you’re wondering what size condensing boiler that you’ll need for your home, then the number of radiators that it needs to supply is one of the best indicators.

  • Up to ten radiators 9-18kW will do the job
  • For ten to fifteen radiators then you’re going to need a 18 to 26kW boiler
  • For fifteen to twenty-five radiators, then look for a 27-40kW boiler

Read our best system boiler guide

Key features

We’ve rounded up all the key features across the different models of the Greenstar 400 range. Do be aware though that not all features will be on all models, so if it’s an important functionality for you, do check that it’s available on the model you’re chosen

Quick tap

How often have you turned the hot water tap on and then waited with the cold water running down the drain until the hot water finally begins to flow? Of course, we could capture that cold water and use it for something else but it’s easy to forget.

However, that wasted water isn’t good for your water bills nor the environment.

The quick tap function means that you can quickly turn on and then immediately turn off your hot water tap and the Greenstar 4000 will prepare the hot water for you. When you then turn the hot water tap back on, thirty seconds later, you’ll be presented with hot water almost immediately.

No more stood by the tap waiting, no more wasted water and improved energy efficiency.

Suitable for areas of low water pressure

Most combi boilers struggle when the water supply has low water pressure.

It can mean that your shower is little more than a trickle and a power shower is the stuff of dreams. The Greenstar 4000 condensing boiler can cope with low pressure meaning that a powerful and warm shower is now a real option.

Fits seamlessly into your kitchen

The Greenstar 4000 measures 400mm by 724mm. That makes it the perfect size to fit between your kitchen cupboards.

Compatible with Bosch EasyControl

Bosch EasyControl provides you with smart control over your heating, all from the convenience of an app. Key features include:

  • Improved energy efficiency – the Bosch EasyControl modulates your boiler, and that means a longer life for your heating system by reducing unnecessary pressure and strain.
  • Ability to control the ideal temperature of each room in the home.
  • Stunning design in a choice of black or white it has a glass touchscreen combined with ambient lighting feature.
  • Super user-friendly and the app can be shared with up to 6 family members so that everyone has control.


Up to ten years of warranty is available on the Greenstar 400. The standard guarantee is for seven years but if you have a Greenstar System Filter fitted, then that goes right up to eight years. Then if you make an additional payment of £150 then it’s extended to ten years.

As with all warranties or guarantees, do make sure that you check out the terms and conditions. There can be requirements for the boiler to be fitted by manufacturer-trained engineers or at the very least gas safe registered engineers. Do check that the boiler installation company have staff who are trained and accredited before committing to any work being done on your home heating system.

You’ll also need to make sure that your condensing boiler is serviced every year and that you have records of that taking place.

Condensing boiler prices can vary depending on the installation costs, so we recommend getting a new boiler quote to get an accurate understanding of what the cost might be.

Viessmann Vitodens 050-W

The Viessmann Vitodens 050 W is a great low-cost option making it a great choice of condensing boiler for homes with up to three bedrooms.

High levels of efficiency

The 050 has an ErP rating of ‘A’ and achieves a fantastic 97% level of energy efficiency on its heating output. This energy efficient boiler loses just 3% of the energy used in producing all of your hot water and heating; that’s pretty impressive!

High quality stainless steel heat exchanger and burner

The heat exchanger and burner are responsible for the efficient conversion of the gas into heat. When you have this combination of stainless steel heat exchangers and burner then your condensing boiler consumes very little of the natural gas during the heating process. That then results in much lower CO2 emissions and as a result, a lower impact on the environment.

The stainless steel heat exchanger also has the advantage of offering much better protection against corrosion. That then means that your condensing boiler will be working more efficiently for longer and so providing another opportunity to save money.

Compatible with tado°

With this easy to use thermostat and smartphone app, you’ll be able to optimise your home heating environment and so make savings on your energy bills. tado° can even recognise when there’s no-one home and it’ll turn the heating off for you. Then, as you arrive home it will begin to heat the home. That means no more accidentally leaving the heating on but also not coming back to a freezing cold house.

Monthy energy saving reports will let you know how efficient the use of your condensing boiler has been.


There’s up to ten years of warranty on offer with the Viessmann 050. If you choose for your condensing boiler to be fitted by heating engineers that haven’t been trained by Viessmann then there are three years of cover on offer.

If your boiler is fitted by a Viessmann trained engineer, then the warranty leaps up to seven years with a chargeable option to take that right up to ten years.

Viessmann have an excellent range of boilers, so we’ve put together a list of all the Viessmann boiler prices for you or view our Viessmann 050 review for more information on this boiler.

Worcester 2000

So, we’re back to Worcester Bosch for the next best condensing boiler on our list. This time we have the Worcester 2000. Worcester considers this one to be a price competitive combi boiler, and it’s a good fit for apartment living along with small to medium homes with one bathroom.

It’s available in two different power outputs, so that’s 25kW and 30kW. It’s also suitable for use with LPG making it a great choice for remote locations as well as static homes and holiday parks.

Key features

Quiet operation

The noise from combi boilers can be distracting especially when they’ve been installed in bedrooms or other living areas. But, the Worcester 200 is the quietest combi boiler in the Worcester Bosch range. No more distractions, no more having to shout over the noise of your old boiler.

Hydrogen compatible

With the move away from gas as the primary fuel for boilers, it’s likely that a 20% hydrogen blend will be introduced in 2025. Thankfully, all Worcester Bosch condensing boilers are hydrogen ready and will need alterations or additional parts fitting when this finally happens.


The Greenstar 2000 combi boiler comes with a 5-year guarantee as standard. If you have this condensing boiler fitted with a Greenstar System Filter, then the guarantee goes up to 6 years and that doesn’t depend on the engineer being trained by Worcester Bosch.

There’s also a ten-year guarantee on the primary heat exchanger.

Read this Worcester 2000 review for further information and specs.

Ideal Logic+ 30

The award-winning Logic+ is from the UK company Ideal. Based in Hull, Ideal was set up in 1906 so they have a pretty strong history in heating even before the introduction of condensing boilers.

The Logic + is available in three different power outputs, 24kW, 30kW and 35kW. That makes this range of condensing boilers suitable for small to medium homes with one bathroom.


The Ideal Logic+ has certainly caught the idea of the sector and has been recognised through awards from Good Housekeeping and the Queen’s awards as well as being endorsed by the Energy Saving Trust.

Quiet Mark Accredited

Logic+ flagship range has been presented with a Quiet Mark award from the Noise Abatement Society That makes them only the second UK boiler manufacturer to receive this status.

Quiet Mark is an internationally recognised award that encourages companies across the world to prioritise noise reduction in their product range.

Frost protection

We all want that peace of mind that our central heating is going to work perfectly throughout the colder months. Ideal have made this so much easier to achieve by installing a frost protection system within the Logic+ 30.

This then means that the condensing boilers in this range recognise when the temperatures drop and then come on for short periods to reduce the chance of ice forming within the pipes.

Aluminium heat exchangers

Rather than a stainless steel heat exchanger, the Logic range of boilers instead have heat exchangers made of aluminium. Ideal find that this gives the boiler much greater heater conductivity, makes them much quieter when operating and provides great protection against corrosion.


The Ideal Logic+ 30 is provided with a 7-year warranty for parts and labour but with a & 10-year warranty provided on the heat exchanger

Read more: Ideal C30 Review

Worcester 8000

Finally for the last in our search for the best condensing boiler, comes the Worcester Bosch 8000.

This model is based upon their top of the range Worcester Beach Greenstar boilers and we think it’s the best combi boiler offered by one of the best boiler brands available.

It has the same modern styling as the 4000, being available in both black and white. If you need a boiler that can cope with the demands of a busy household, then this could be a good option.

This range is available both as combi boilers and as a system boiler but whichever you need, it’ll be condensing boilers on offer.

Range of power output options

The system boiler models within the range are available in 30kW and 35kW power outputs. The combi boiler though provides five different power output options, 30kW, 35kW, 40kW, 45kW and finally, 50kW.

This then means that Worcester 8000 range of condensing boilers, including the combi boilers, is suitable for larger homes with multiple bathrooms.

Using a boiler size calculator can help decide what system you need for your home.

Optional intelligent filling system

The Greenstar Intelligent Filling System is a first within the sector and is an optional extra for new condensing boilers.

It works by ensuring that the Greenstar 8000 Lifestyle range always maintains an optimum boiler pressure and it does this through a software package.

This revolutionary approach provides access to the workings of the internal filling valve so that it can fill the heating system automatically as and when needed. Once the correct pressure has been achieved, then the integrated filling valve will be closed.

This then means that there is no possibility of overfilling the heating system and it also lets you know if there is too much pressure being lost.

Key features of the intelligent filling system

  • Worry free heating and hot water
  • The system pressure is maintained automatically
  • Reduces the need to call out an engineer for pressure-related issues
  • Identifies if there is a leak in the system and prevents the boiler from overfilling

At the moment, the Intelligent Filling System is only compatible with combi boilers and no other type of condensing boilers.

Guarantee period

An industry-leading 12-year guarantee period is on offer when you have a condensing boiler installed by a Worcester Accredited Installer.

There are other criteria to meet to ensure that the guarantee period is honoured and this will include the need to have the boiler serviced on an annual basis by an engineer who is gas safe registered.

For all the information you need on this model, take a look at our Worcester Bosch 8000 review

Our verdict on the best condensing boilers

This was a tough list to compile because there are just so many great options. It doesn’t matter whether that’s for gas boilers, LPG or even oil boilers or even whether you’re looking for the convenience of even the best combi boiler or the power of system boilers.

The boiler manufacturers are now providing us with more and more great boilers to choose from.

If we were able to sneak a few more onto the list of the best condensing boilers, then we would have added the Vaillant ecotec plus, the Viessmann Vitodens 100 W and Baxi Boilers 800 combi.

All of these models warrant being on the list for the best combi boilers with each one offering a whole range of functionality while also being very energy-efficient boilers.

But no matter which new boiler you decide upon with being condensing units you can be sure that they will be more energy-efficient and have lower levels of carbon emissions compared to the old non-condensing boilers.

If you’re now looking to have a condensing boiler installed in your home then the first step is to get a new boiler quote.

Not only will we make suggestions for the best new boiler for your home along with details of the boiler prices, but you’ll also be able to find out when the next date is to get your boiler installed. This could be in as little as a couple of days.

Some companies, such as Boiler Central offer boiler finance to spread the cost of your replacement boiler.

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