First Published: October 20, 2020. Updated: April 17, 2023
Best System Boilers
We understand that searching for the best system boiler can be a challenging task with so many different boiler manufacturers, outputs and options available. However, that’s where we come in. As an independent boiler installation company, we’ve done the hard work for you and compiled this guide to the best system boilers available to purchase in 2023.
What does this review cover?
What makes a good system boiler?
Choosing the best size system boiler for your property
What is the best size system boiler for a one/two bedroom property?
What is the best size system boiler for a three-bedroom property?
What is the best size system boiler for a four-bedroom property?
Top 3 system boilers
What makes the best system boiler?
Putting the brand and technology utilised within the boiler aside for a minute, the best system boiler ultimately is one that is correctly sized to efficiently accommodate your heating needs. By choosing the wrong sized boiler, you will either end up spending more on your energy bills than you need to, or your home won’t be provided with the heat it requires.
At Boilerhut, we have a team of engineers with 40+ years of experience and we have called upon them to produce a list of the top 5 system boilers currently available in the UK. In addition to their experiences installing, maintaining and servicing these boilers, we have also considered the following to produce this list:
- Material quality
- Flow rate
- Customer feedback
- Customer service
- Awards and accolades
Top 3 system boiler brands
A German boiler manufacturer. Viessmann was established in 1917 and entered the UK market in 1989. However, it is only in the last decade or so that Viessmann has begun making its mark in this country. Prior to this, Viessmann’s UK operations were focused upon the industrial and commercial boiler market.
We are pleased to say that they have taken this expertise and effectively translated it into the domestic market. Whilst still not a household name in the UK, Viessmann is the largest boiler manufacturer in Europe.
We are confident in saying that Viessmann offers the best system boilers available on the UK market in 2023.
Our engineers’ thoughts on Viessmann
The Viessmann Vitodens 100-W System boiler is a fantastic and reliable wall mounted gas condensing boiler, having been awarded Which? Best Buy status in 2017, 2018 and 2019.
These gas system boilers are available from £2600 installed, which comes in at the average price for a system boiler and in the range there are affordable boiler options for larger homes with a higher hot water demand.
The Vitodens 100-W Gas System Boiler comes in 11kW, 19kW, 25kW, and 32kW outputs.
The Viessmann Vitodens 100-W System Boiler comes with an efficient and reliable Inox-Radial heat exchanger with MatriX cylinder burner.
The cylinder ensures the heat is distributed cleanly and efficiently and won’t corrode or fail as with most other boilers.
With a high modulation ratio of 1:10, the boiler reduces or increases its operating power for any given room environment. This reduces heating bills and wear and tear.
The LCD touchscreen makes this system boiler easy to use, and It also comes with an optional external weather detector. What does this mean? It means that the detector allows the boiler to react to outside weather conditions and increase or decrease temperatures accordingly.
This system boiler rates ‘A’ Class in the SEDBUK energy efficiency ratings.
- High modulation ratio of 1:6
- SEDBUK A Rating
- MatriX pre-mix cylinder burner and an integral AquaBloc hydraulic unit
- Very quiet boiler – operating at just 35 dB
- Compatible with an external weather detector
- LCD touchscreen
- Wifi and remote monitoring for ongoing support
- Hydrogen ready for 2022
Overall, we would recommend this system boiler above all others due to its quality, performance, lengthy warranty and price.
You can discover our more detailed thoughts on this boiler in our Viessmann Vitodens 100-W Review.
2. Worcester Bosch
Worcester Bosch has been a permanent fixture in the UK boiler market since being established in 1962. Since then it has become a household name amongst UK consumers. Many consumers choosing the brand time and time again because they know the name or already have a Worcester Bosch boiler installed.
Put simply, Worcester Bosch has an enviable reputation in the UK. This is for good reason. For many years Worcester Bosch has offered high-quality system boilers to their customers. All of which are backed up by the global reputation and engineering might it has gained since becoming part of the Bosch group in 1992.
Worcester Bosch is the UK market leader in domestic boilers. And has built up an excellent reputation over the last 50 years. Becoming a household name in the UK. During this time, they have also received a Royal Warrant for supplying boilers to Her Majesty The Queen’s Sandringham Estate.
Our engineers’ thoughts on Worcester Bosch
The Worcester Bosch Greenstar i System Boiler is one of a range of highly energy-efficient A-rated gas boilers.
Available in a vast array of outputs, the Greenstar i System Boiler comes in 9kW, 12kW, 15kW, 18kW, 21kW, 24kW, 27kW and 30kW.
Like the Viessmann above, it’s not just us who recommend this boiler, the Greenstar i System Boiler received a great score in the 2020 Boiler Brands report carried out by Which? and has been awarded Which? Best Buy status.
The Greenstar i range is split up into two sections, the boilers from 9kW to 24kW, and the 27kW and 30kW outputs of the boilers. The latter two boilers being part of a new generation of boilers from Worcester Bosch which are smaller, lighter and are designed to be able to fit in a kitchen cupboard. The main range being slighter larger and heavier and is designed for wall-mounting.
With this vast array of outputs, the Greenstar i range offers solutions for homes from a small flat or bungalow with up to 5 radiators, to a larger family home with up to 14 radiators.
Offering up to 94% efficiency, it is equivalent to the Viessmann Vitodens 100-W Gas System Boiler.
However, we have ranked this boiler lower than the Viessmann Vitodens 100-W as it has an aluminium heat exchanger, as opposed to Viessmann’s stainless steel heat exchanger. The issue here is that aluminium heat exchangers are much more prone to corrosion than their stainless steel alternatives and this will affect efficiency over time.
To Worcester Bosch’s credit and the reason we are recommending this boiler, they do offer a 10-year guarantee on the heat exchanger. This means that you are covered for 120 months against any issues with the heat exchanger due to any faults or defects relating to its manufacture.
As part of this cover, the heat exchanger will be repaired free of any material charges during the 10 year period. However, you will be liable for labour costs if the boiler is out of the main product warranty period. This is a slight downside as the Greenstar i only comes with a 5-year warranty, as standard – this is extendable to 10 years though if installed by a Worcester Accredited Installer.
As we have mentioned regarding new boilers and their efficiency, there are reasons why the new system boilers are so good. One example on the Worcester-Bosch Greenstar i is that it recycles the heat from exhaust gases that would otherwise be lost through the flue. It then takes this heat and modulates its output independently for domestic hot water and central heating. This means that the Greenstar i is up to 30% cheaper to run than some older boilers.
- ERP rating: A
- 94% efficiency
- LPG compatible
- 5-year standard warranty
- Can be used with Greenskies solar panels for energy and cost savings
- Low energy pump reduces electrical usage
- Large Condensesure style siphon built into the boiler to eliminate frost risk
Navien is a very new entrant. Not just to the UK combi boiler market but the UK boiler market in general. Despite this, we see big things for this South Korean boiler manufacturer. We tip it to be the recipient of multiple prestigious UK awards in the next few years.
It should be noted that whilst Navien is a new entrant to the UK market, having only been here since 2014 and having only offered system boilers since 2017, it is a major player internationally. They are the world’s best-selling boiler brand. Its production facility in Seotan, South Korea, is the largest boiler production facility in the world. As you would expect with such accolades, Navien is already making waves in the UK market with its use of innovative technology.
Our engineers’ thoughts on Vaillant
The Vaillant ecoTEC is Vaillant’s flagship boiler and was first launched in 2015. Like both the Viessmann and the Worcester Bosch we recommended before it, it has also been awarded Which? Best Buy status.
Our initial thoughts on the Vaillant ecoTEC Plus System Boiler is that it is an easy to use, reliable and quiet boiler. It’s not quite as efficient as the Viessmann and the Worcester Bosch but it still comes highly recommended by us.
We particularly like the ecoTEC Plus System Boiler due to its smart features such as its ability to recognise when you don’t need as much heating power, which can allow it to drop to using 16% of its maximum power saving on fuel and money.
We also like the quiet operation of the boiler, operating at just 44 dB and accredited by Quiet Mark, as a result.
With six outputs available from 12kW to 37KW, this is another boiler range which has an option available for the smallest properties to larger properties.
Importantly, we recommend this boiler due to the fact that it has a stainless steel heat exchanger, just like the Viessmann. This is important because of stainless steel’s resistance against corrosion and abilities in ensuring efficiency throughout the lifetime of the boiler.
Its straightforward backlit display, simple user controls including an on and off switch, reset button, pressure gauge and heating temperature control, all makes the ecoTEC Plus System Boiler an easy to use boiler.
Like the Worcester Bosch, the ecoTEC Plus System Boiler also comes with a 5-year guarantee, as standard – again though, this can be extended to up to 10 years if installed by an accredited installer, in this case that’s a VaillantAdvance installer.
The only reason we ranked this boiler higher than the Worcester Bosch option is due to the cost, whilst it’s only around £100 more to get the lowest output option installed, the higher output models can get much more expensive when being installed by a VaillantAdvance installer. That said, it is a great boiler nonetheless.
- Stainless steel heat exchanger
- Advanced modulation during low usage to ensure maximum efficiency
- New high-efficiency pump to reduce energy consumption
- Stylish contemporary case design
- Backlit display
- ErP A rated for both hot water and heating efficiency
- Quiet Mark accredited
- Compatible with a wide range of heating controls including Vaillant’s vSMART™ smartphone app