Best System Boilers in 2025

Are you looking to have a new system boiler installed in your home and are wondering what distinguishes a bad system boiler from a good one? 

System boilers are one of the most common types of domestic boilers in the UK and a popular choice among larger homes with multiple bathrooms. 

So which brands offer the best system boilers? What matters? Size, brand name, warranty period?

In this post, we considered all of the most important factors. 

PS We fit new system boilers with gas installation nationwide. Simply answer these questions, get your fixed price and you could get it installed as quick as tomorrow.

To determine which are the best system boilers available in 2024, we considered the following factors:

• Warranty period offered by the brand 

• The overall reputation of the brand based on customer reviews 

• Trustpilot reviews  

• Awards and accolades e.g. Which? Best Buy Awards

• Customer service performance 

• The price range of their boilers  

• Efficiency ratings

Best System Boilers in the UK (By Brand)

#1 Worcester Bosch System Boilers (Best) 

Worcester Bosch remains one of the most popular boiler manufacturers in the UK and remains a popular choice to install among engineers. 

But why else do we think the brand is worthy of the #1 spot? 

• Which? Best Buy Award for over 10-years  

• 10-year guarantee (when purchased via Heatable)

• Availability of parts is second to none 

• Excellent customer reviews and aftercare

• High-efficiency A-rated combi boilers 

Worcester Bosch 4000 System Boiler 

The Worcester Bosch 4000 system boiler is one of Worcester's latest innovations and officially replaced the best-selling Greenstar i model. 

It offers everything you could possibly want in a system boiler but with some major improvements, including a quieter operation and higher hot water output. 

The 4000 system boiler also features a revamped exterior. This includes a sleek curved edge case, user-friendly digital display and easy to use push control buttons, a huge advance on the now-retired Greenstar i. 

Main Features of the Worcester Bosch 4000 system boiler: 

• Compatible with all Worcester Bosch controls and third-party controllers such as Hive, Nest, tado etc.

• Ideal for medium sized homes with multiple bathrooms

• Easy access with removable side panels

• 10-year guarantee on parts and labour (when purchased via Heatable) 

• ErP rating 94%: A-rated

The system boiler is a wall hung unit available in either white or black and requires a separate hot water storage cylinder. 

The Greenstar 4000 System boiler is available in the following power outputs:

• 12kW

• 15kW

• 18kW

• 21kW

• 24kW

Read our full review of the Worcester Bosch 4000. 

#2 Viessmann System Boilers (Second Best System Boilers)

Viessmann is a relatively new boiler manufacturer in the UK's residential heating market but is by no means a new entrant and in fact, has been dominating the continental market for decades. 

Renowned for its German engineering, reliability and superb customer support, the brand has risen to become one of the most respected brands from both the viewpoint of customers and engineers. 

Major benefits of Viessmann boilers include: 

• Technically brilliant boilers e.g. they use stainless steel heat exchangers

• 10-year guarantee (when purchased via Heatable)

• Excellent customer reviews and aftercare

• High-efficiency A-rated combi boilers 

Viessmann Vitodens 100-W System Boiler

The Viessmann Vitodens 100-W is officially the brand's best selling model, which is also available as a combi boiler. 

Recently revamped, the new 2021 model features a new and improved exterior design, hydrogen-ready technology and an upgraded backlit LCD touchscreen display. 

The latest Viessmann Vitodens 100-W also features wi-fi capability allowing you to control and diagnose any boiler issues more easily.

This ingenious feature also enables remote access to Viessmann support so that they can assist from afar and diagnose faults. 

The touchscreen display also expands on the usual error code system and actually shows you which components have failed and may be causing the fault. This helps to alleviate the costs associated with diagnosing faults using a generic and broad error code. 

Main features of the Viessmann 100-W system boiler:

• Class 'A' for energy efficiency

• 10-year comprehensive warranty as standard - when purchased with Heatable

• 89.5% efficiency

• Hydrogen-ready for the next generation of fuel 

• Backlit LCD touchscreen display 

• Stainless steel heat exchanger 

• Compatibility with the Viessmann Vitronic smart thermostat 

The Viessmann 100-W System boiler is available in the following power outputs:

• 11kW

• 19kW

• 25kW

• 32kW

Read our full review of the Viessmann Vitodens 100-W. 

#3 Alpha Boilers (Third Best System Boilers)

Headquartered in Kent, Alpha boilers are an award-winning Italian boiler manufacturer that is competitively priced and offers boilers that are technically brilliant from an engineering and performance perspective. 

Major benefits of Alpha boilers include: 

• Technically brilliant boilers e.g. they use stainless steel heat exchangers

• 10-year guarantee (when purchased via Heatable)

• Excellent customer reviews and aftercare

• High-efficiency A-rated system boilers

Alpha E-Tec System Boiler 

The Alpha E-Tec is Alpha Innovations most popular system boiler and although it is considered a budget-friendly brand, it uses a stainless steel heat exchanger as opposed to aluminium, which is usually only seen in premium brands. 

Important note: Stainless steel tends to last longer than aluminium as it's more resistant to heat and corrosion. 

When purchased via Heatable, the E-Tec is also offered with a very generous 10-year warranty, which is again typically only available with market-leading brands, such as Worcester Bosch. 

The Alpha E-Tec system boiler is the perfect solution for households on a budget who care about securing a boiler engineered with longevity in mind. 

Main features of the Alpha E-Tec System boiler:

• Alpha’s best selling combi boiler 

• Designed to neatly fit into small spaces like kitchen cupboards 

• Easy access front panel making servicing quick and easy 

• Built with a stainless-steel heat exchanger 

• Compatible with all leading third party controls such as Hive, Nest, tado etc.

• High-efficiency Grundfos pump and hydroblock assembly

• Zinc plated expansion vessel to prevent corrosion

• 10-year guarantee on parts and labour (when purchased via Heatable) 

• ErP rating 93%: A-rated

• Dimensions: 712 x 440 x 255

• Good Homes Magazine Approved (2021) 

The Alpha E-Tec System boiler is available in the following power outputs:

• 28kW

• 38kW

#4 Ideal Boilers (Fourth Best System Boilers) 

Founded all the way back in 1906, Ideal are an industry heavyweight in the UK renowned for offering competitively priced, reliable boilers and more recently, for becoming the official mascot of West Bromwich Albion F.C. (a.k.a Boiler Man). 

Major benefits of Ideal boilers include: 

• Made in the UK 

• Compact in size (ideal for cupboards) 

• Won the Queens Award in 2013 

• Won Good Housekeeping Award 2013 & 2017 

• Quiet Mark Certified - an award for especially quiet appliances 

• 10-year parts and labour warranty (when purchased via Heatable) 

Ideal Logic System Boiler 

The Ideal Logic system boiler is the boiler manufacturer's staple and most popular system boiler model and one of the most competitively priced available when comparing the major brands. 

The Ideal Logic system range also stands out thanks to its compact dimensions, which make it small enough to fit into a typical sized kitchen cupboard, which certainly can't be said for all system options available. 

Main features of the Ideal Logic System boiler: 

• Compact design - able to fit into kitchen cupboards 

• Backlit digital display for easy reading and adjustment of the pressure gauge

• Built-in service indicator – reminding you when it is time for a service (to ensure your warranty stays valid)

• Boiler frost protection 

• Built-in programmer, allowing you to set a 7-day schedule 

The Ideal Logic system boiler is available in the following power outputs:

• 15kW

• 18kW

• 24kW

• 39kW

Read our full review of the Ideal Logic. 

Related boiler guides: 

• What is a boiler and how does it work? 

• Boiler maintenance tips. 

• What should boiler pressure be when the heating is on? 

• Should I turn my heating off when I go on holiday? 

• How to pay for a new boiler.

• How much can a new boiler save you? 

• Boiler warranties explained. 

#5 Vaillant System Boilers (Fifth Best System Boilers) 

Vaillant is yet another German boiler manufacturer with a stellar reputation among industry professionals and consumers. Among installers, they are often credited with being one of the easier brands to repair. 

Due to their impressive reputation for being reliable and well-engineered, Vaillant sells a lot of boilers and is in fact the second largest boiler manufacturer in Europe.  

Major benefits of Vaillant boilers include: 

• Hand-built in the Derbyshire-based plant in the UK 

• A complete range of thermostat controls

• Awarded the Which? Best Buy Award in 2016 

• Quiet Mark status - awarded to the quietest boiler models 

Vaillant EcoTec Plus System Boiler 

The EcoTec Plus is Vaillant's best selling system boiler model and is built with quality in mind. As a result, this offering is considered a premium option, so expect to pay a little more than most brands. 

As well as German engineering and amazing customer service and aftercare, the EcoTec Plus boiler comes with some extremely innovative features that help to enhance efficiency, servicing and boiler maintenance. 

Notable features of the EcoTec include vSMART, an application allowing you to easily control the boiler from your smart devices. It includes popular controls like weather compensation that enables you to reduce energy waste and save money on your heating bills. 

The Vaillant EcoTec system boiler is available in the following power outputs:

• 12kW

• 15kW

• 18kW

• 24kW

• 30kW

• 37kW

Read our full review of the Vaillant EcoTec. 

System Boilers Frequently Asked Questions (FAQ) 

Here are some of the most frequently asked questions and answers about system boilers:

What is a System Boiler?  

A system boiler is a type of boiler designed to cope with high hot water demands e.g. properties with multiple bathrooms where a traditional combi boiler may struggle to maintain adequate water pressure. 

They are very similar to regular (conventional) boilers in that they deliver hot water directly to the central heating and store hot water within a hot water cylinder.

However, system boilers are essentially an upgrade to the regular boiler. They benefit from more internalised parts, including an internal pump and they take their water directly from the mains. 

This benefit means they don't require as much space as a regular boiler e.g. a cistern tank in the attic, and it also means they are able to provide a more consistent level of water pressure. 

How Does a System Boiler Work? 

A system boiler has two main components - the boiler itself and the hot water storage cylinder. 

For heating: 

To provide your home with heating, the boiler is fed with water directly from the mains water supply, which in turn is heated directly by the boiler and then circulated to the radiators around your property. 

For hot water: 

To provide your home with hot water e.g. to the water outlets like your shower and hot taps, the system boiler keeps a store of hot water within the hot water storage cylinder. This is then supplied to the outlets as they are used, enabling the pressure to be maintained, even if multiple bathrooms are in use. 

Recommended heating guides:

• System boilers vs combi boilers

• Best 40kW system boilers

• What is a boiler filling loop?

• How much does a powerflush cost?

• How to turn off a radiator

• How do you know if your boiler is condensing?

Is a System Boiler right for my home? 

Combi boilers are the most popular type of boiler installed in UK homes since they are typically the easiest type of boiler to install and are compact, meaning they only need a limited amount of space. 

They are also fed with water directly from the mains, so can provide on-demand hot water, however, for homes with high hot water demands, they can sometimes struggle to maintain adequate water pressure. 

For this reason, system boilers are often recommended for larger homes with multiple bathrooms and with greater demand for hot water. This is especially true in homes where water outlets are likely to be used simultaneously e.g. two showers being used at the same time. 

What size system boiler do you need? 

Wondering what size system boiler you need?

Here's a basic breakdown: 

Essentially, for small to medium-sized homes – allow 1.5kW per radiator + 3kW for your cylinder.

For something way more comprehensive, read our boiler size guide.

Don’t like maths? Let Heatable do the whole thing for you – get quotes.

How much do System Boilers Cost? 

Typical Heatable costs for Ideal Logic system boilers, based on a straightforward like-for-like system boiler swap.

*2024 update: Due to increased numbers of client-reported issues, Heatable no longer supplies and fit Ideal boilers.

Typical Heatable costs for Viessmann system boilers, based on a straightforward like-for-like system boiler swap.

Check out our new boiler costs guide for something more comprehensive and if you want to know which boiler to choose, see our best condensing boilers review. 

Related domestic energy guides: 

• When will gas boilers be banned? 

• How much energy do appliances use? 

• Who qualifies for a boiler grant? 

• Boilers on finance. 

• Best combi boilers in the UK. 

• Open vented boilers. 

Looking for the best deal on a new System Boiler? 

If you’re aiming to get the best deal on a new boiler, consider getting a quote from us, here’s why:

• Gas Safe installation within 24 hours.

• Thousands of satisfied customers with an average score of 4.9 on Trustpilot, surpassing the market leader.

• Which? Trusted Trader: Heatable is proudly recognised as a Which? Trusted Trader.

• Price match guarantee: We will match any like-for-like cheaper quote.

• Flexible payment options, including interest-free finance*.

• Up to 12-year guarantee on selected boilers.

• Fixed price guarantee: No hidden costs.

• Save your quote and decide later.

• Get an instant fixed price on a new boiler, here.

To learn more about boilers, visit our advice section, check out our YouTube channel, or read customer testimonials here.

Heat Happy.

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