Best System Boilers: Which System Boiler is Best in 2021?

best system boilers

System boilers are common across UK households, especially for those with more than four people or more than one bathroom. Here, we provide advice on the best system boilers for 2021 and beyond.

If you’re unsure whether you need a system boiler or a combi boiler, take a look at our guide System vs Combi Boilers: Which Is Best.

If you’re ready to dive in, then let’s take a look at the best system boilers in 2021 and save you some time and money. And don’t forget to compare against other boiler types and compare with our guide to boiler costs too.

Get an online fixed price in 20 seconds:

Q What kind of fuel does your boiler use?

The best UK system boilers for 2021 are:

  • Viessmann Vitodens 100-W System
  • Worcester Bosch Greenstar i System
  • Vaillant ecoTEC Plus System
Viessmann 100-W 26kW Regular Open Vent
Vitodens 100-W

1. Viessmann Vitodens 100-W Gas System Boiler

The Viessmann Vitodens 100-W System boiler is a fantastic and reliable wall mounted gas condensing boiler. 

These gas system boilers are available around £1000 making it a great choice for any home who wants a top-quality but cheap system boiler.

It comes in 26kW, 30kW, and 35kW system boiler sizes.

This system boiler will be perfect for larger homes with more than one bathroom who demand water to multiple taps at once.

For a boiler quote in 20 seconds – click here

What do we love about this boiler?

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 1:6, 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.

Main Features:

  • High modulation ratio of 1:6
  • SEDBUK A Rating
  • MatriX pre-mix cylinder burner and an integral AquaBloc hydraulic unit
  • Various Kw Heating Output -26kW, 30kW, and 35kW
  • Very Quiet Boiler
  • Optional external weather detector
  • Advanced technology
  • Which Rating 76%
  • LCD touchscreen
  • Compact size
  • Lightweight
  • 5- year parts and labour warranty as standard (Up to 10 years with Viessmann Installer)

Overall, we would recommend this system boiler above all others due to quality, performance, lengthy warranty and price. 

With installation, you can expect a cost between £1800-£2200 depending on the company who installs it. 


If you’d like a new system boiler quote, then click here as we can provide you with a custom quote including installation fees for your home specifically so you can get an idea of the total cost for you. 

2. Worcester Bosch Greenstar 24i System Boiler Reviews

best system boilers 2020
greenstar i boiler system boilers 2021

The Worcester-Bosch Greenstar 24i System is one of a range of highly energy-efficient A-rated gas boilers.

They are rated very highly by SEDBUK 2009.

Being a system boiler, the Worcester-Bosch Greenstar 24i System requires a hot water storage cylinder; however, it doesn’t require a feed and expansion cistern.

This makes the Greenstar 24i a quick and easy boiler installation as well as being efficient and economical to run.

What do we love about this system boiler?

With the Worcester-Bosch Greenstar 24i, heat from exhaust gases, that would otherwise be lost through the flue, are recycled. This heat is then used as output, powering your domestic hot water and central heating with what otherwise be wasted energy.

This means that the Greenstar 24i is up to 30% cheaper to run than some older boilers.

We rate this boiler lower than the Viessmann because the Viessmann has a much better stainless steel heat exchanger with better reliability than the Worcester Bosch. 

The price comes in around £1,050 on average with an installed price being around £2000. 

Get an online fixed price in 20 seconds:

Q What kind of fuel does your boiler use?

Main Features:

  • ERP rating: A HEAT
  • Efficiency Rating: 94%
  • Band Rating: A Rated
  • LPG Compatible: Yes
  • Standard Warranty: 5 Years
  • kW Options: 24.6 kW
  • Mounting: Wall-mounted

Overall, with the price and efficiency, we recommend this boiler in 2nd place to the Viessmann.

After our extensive research, going through customer reviews, looking at our own customer’s experiences, asking our Gas Safe heating engineers about fitting, reliability, etc.

You can be sure that our information is reliable and will give you a fantastic new system boiler. 

3. Vaillant ecoTEC Plus System Boiler

Vaillant EcoTEC System Boiler 2021

The ecoTec boiler range from Vaillant is a fantastic and low energy consumption system boiler for 2021.

It has excellent performance for hot water and central heating – and lower fuel bills for you. 

The Vaillant ecoTec 30kW is the most popular size boiler in this range, but it is also available as 12kW, 15kW, 18kW, 24kW, 30kW and 37kW.

The ecoTEC plus is smart: when it knows you don’t need as much heating power, it can drop to using 16% of its maximum power saving on fuel and money.

It is known by our installers to be efficient, easy to use, reliable and quiet.

With its straightforward backlit display and like the Viessmann, its stainless-steel heat exchanger and it’s premium components, it’s really one of the top system boilers available on the market today.

We only rated this in third place due to the initial cost.

It does have a better heat exchanger than the Worcester Bosch however its initial cost is almost £500 more than the other two system boilers. 

Pricing is around £1500 with an installed price of £2000+

Get an online fixed price in 20 seconds:

Q What kind of fuel does your boiler use?
vaillant eco tech best system boilers 2020

Vaillant System Boilers Features:

  • For use with Unvented Systems.
  • 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 to ensure a seamless fit with home decor
  • ErP Compliant
  • Lightweight and compact
  • Natural Gas fueled
  • Includes 2 stage frost thermostat
  • Built-in pump and expansion vessel
  • Compatible with Unvented systems

Overall, an excellent boiler with reliable internal components means you can’t go too far wrong with the Vaillant EcoTec series system boilers.

What’s the average cost of a system boiler in 2021?

boiler pressure

The average cost of the best UK system boilers in 2021 is around £1,750.

The low end of the range is around £1000, whereas the top end boilers systems come in around the £3000+ mark.

Remember that boilers are one of the most important features of your home in terms of use and cost, so picking the right one is paramount to having a warm and cosy place to live. 

Get an online fixed price in 20 seconds:

Q What kind of fuel does your boiler use?

Do you need a new system boiler in 2021? 

If you’re here because you are looking for a new gas system boiler or any other fuelled system boiler, then welcome to our guide.

However, now we’ve discussed our recommended system boilers, let’s identify whether you need a new boiler.

Get an online fixed price in 20 seconds:

Q What kind of fuel does your boiler use?

Is it worth getting a new system boiler?

Viessmann 100-W 35kW Regular Open Vent

For the eco-friendly benefits and the green nature of modern boilers, we would recommend upgrading. 

If you want to save money on your bills, go ahead and get a new system boiler!

This is because they are now so efficient that the savings over the years on your bills will more than pay for your new system boiler. 

How much money can I save?

The energy-saving trust’s guide for 2021 says that the new system boilers can save you more than £340 a year on your heating and hot water costs. 

The warranties last longer, as do the system boilers:

The modern system boiler can have warranties starting at 10 years and go higher or lower depending on the manufacturer.

Viessmann system boilers offer a 12-year warranty at Boiler Central whereas Vaillant offers up to 10 years warranty.

viessmann warranty

Also, the internal components are much more reliable and make sure of more advanced digital features such as automatic frost protection, etc. 

What is the best system boiler?

The Viessmann 100-W tops the best system boilers on the market today. They even have Which? Best Buy boiler accreditation!

If you’ve been looking for the best system boilers in 2021, we hope that the above information has been of value to you and helps you in your search. 

If you would like a custom boiler quote calculator which gives you a specific price, then please see our website as we offer this service with no obligation. 

For a boiler quote in 20 seconds – click here

Should you require boiler cover to help you keep your boiler serviced and in optimal working order, we can provide this too for as little at £13.99 a month. 

Thanks again and stay tuned to our website for more valuable boiler advice and tips and tricks. 

Get an online fixed price in 20 seconds:

Q What kind of fuel does your boiler use?

Get a great price on a Which? Best Buy boiler online in minutes

Pick your install date | £0 Deposits | 0% Interest-FREE
12-Year Warranty on Worcester Bosch & ViessmannGet a Quote Now >