James Elston

Published April 9, 2024

Choosing the best system boiler for your home can be tricky, especially when you’re faced with endless boiler options. Whether you live in a flat or a large house, understanding the basics of boiler functionality, specs, and fuel types is important to make an informed decision.

Decide which fuel type works best for your home. Electricity, gas, and oil prices must be considered to figure out which is the most cost-effective boiler to run. All of the system boilers on our list are powerful models and can cope with high hot water demands.

Our top pick is the Viessmann Vitodens 100-W due to its advanced features and amazing efficiency ratings – among other things.

We haven’t been this excited about 2024 heating trends in a while – let us guide you through these heating solutions.

How We Chose The Best System Boilers

Here’s how we chose the five system boilers that appear on this list.


One of the key things we evaluated was the reliability of the system boilers that are currently available. To do this, we found customer reviews on sites like Trustpilot that specifically mentioned reliability. 

Any boilers that consistently required repairs were ruled out, and the ones that ran efficiently without the need for much maintenance were considered for inclusion on our list. 


We also considered the number and quality of the features included with each boiler. We looked out for things like stainless steel heat exchangers, compatibility with smart controls, condensing technology, and intelligent filling systems, 

Output ratings

Output ratings, in terms of kWs, are absolutely crucial as they determine how powerful a system boiler is and what size home it’s most suitable for. We awarded points to system boilers that came in a range of different outputs, as this indicates versatility and suitability for a number of different home sizes. 


We only chose system boilers that are A-rated for efficiency. This means they had to achieve an efficiency percentage of at least 92%. These ratings are essential to ensure a boiler is cost-effective and environmentally friendly. 

In-Depth Analysis Of The Top 5 System Boilers

Now that we know what features to look for, let’s take a squiz at a few models from top-rated boiler brands. These are the best system boilers for 2024 – the ones you want to consider when figuring out which new system boiler to go for.

1. Viessmann Vitodens 100-W System Boiler

  • Warranty: Up to 12 years extended warranty
  • Fuel types: Gas, LPG, oil
  • System types: Combi, system, regular
  • Dimensions: 400 mm (w), 700 mm (h), 350 mm (b)
  • Price (for system boilers): 19 kW = £1,025; 25 kW = £1,055; 32 kW = £1,200


The Viessmann Vitodens 100-W is a popular system boiler (and one of our best 40kw system boilers) that has been installed in many UK homes. It’s known for its strong German engineering, reliability, and advanced features like built-in Wi-Fi and a user-friendly LCD touchscreen.

It has a 94% energy efficiency rating and its compact design makes it suitable for various home-size installations. Its stainless steel heat exchanger is guaranteed to last for years to come, beating the likes of its aluminium counterparts.

These Viessmann boilers include a 4-pipe system which is ideal for larger homes with higher hot water demands. Not to mention they’re hydrogen boilers too, using a 20:80 blend of natural gas and hydrogen – slashing greenhouse gas emissions and reducing your carbon footprint.

2. Worcester Bosch 4000 System Boiler

  • Warranty: 10 years
  • Fuel types: Gas, oil, LPG-compatible system boilers
  • System types: Combi, system
  • Dimensions: 710 mm (w), 400 mm (h), 310 mm (b)
  • Price (for system boilers): 12 kW = £1,100; 18 kW = £1,200; 24 kW = £1,300


A Worcester Bosch 4000 System Boiler is the latest addition to the Worcester brand, surpassing its predecessor, the Greenstar I range. It’s fitted with intelligent filling system programs that ensure boiler pressure is always kept within the optimum range, and its nifty built-in Wi-Fi allows homeowners to monitor energy usage from afar.

To add to its functionality, these system boilers are equipped with LCD touchscreens, ‘Quick Tap’ features (for instant hot water), ‘Quiet’ system boiler options (45 dB), and thermostatic radiator valves, so you can adjust individual room temperatures with the twist of a knob.

The Worcester Bosch 4000 is an A-rated energy-efficient heating system with a 94% rating. In other words, out of every £1 spent, 94p is used to generate hot water and warmth. These are the best system boilers for larger homes as they produce hot water very quickly.

Opt for this system boiler if you’re environmentally conscious. Not only does the 94% energy efficiency rating reduce carbon emissions, but Worcester packaging is 99.9% recyclable. All in all, these boilers are fantastic, energy-efficient heating solutions.

3. Worcester Bosch Greenstar i System Boiler

  • Warranty: 10 years – when installed by accredited Worcester heating engineers
  • Fuel types: Gas, LPG
  • System types: Combi, system
  • Dimensions: 400 mm (w), 710 mm (h), 330 mm (b)
  • Price (for system boilers): 30 kW = £1,150


The Worcester Bosch i30 System Boiler is a popular central heating system. It’s a high-quality gas system boiler that is suitable for a wide range of homes. Its lightweight and compact size makes installations easy. It’s also compatible with a smart thermostat.

The simple control panel is easy to navigate and is compatible with Bosch EasyControl, making remote monitoring a breeze. These compact units use condensing technology, where they return unused water to the boiler for reheating. This reduces the amount of heat loss, saving you money on your energy bills.

The 25 kW system boiler is perfect for smaller one-bedroom homes, while the 30 kW model seriously brings the heat. These A-grade central heating systems with a 94% efficiency rating also reduce your carbon footprint.

While they don’t have a stainless steel heat exchanger, spare parts are widely available across the UK.

4. Vaillant ecoTEC Plus 624 System

  • Warranty: 10 years
  • Fuel types: Gas (not compatible with LPG)
  • System types: System
  • Dimensions: 440 mm (w), 720 mm (h), 340 mm (b)
  • Price (for system boilers): 24 kW = £1,227


The Vaillant ecoTEC System Boiler is the brand’s flagship boiler model, designed to store hot water in a separate storage cylinder. It’s so smart that it drops to 16% of its maximum power output when heating has subsided – earning itself the QuietMark stamp of approval for its ultra-quiet performance.

This compact-size system boiler is ideal for medium-sized homes and provides enough heat for dwellings with around 15 radiators.

It’s a highly efficient boiler model (94%) fitted with advanced modulation, flame detection and condensing technologies. These systems work together to reduce your energy bills and carbon emissions – bringing the UK’s net-zero goal closer to home.

5. Alpha E-Tec System Boiler 

  • Warranty: 10 years
  • Fuel types: Gas
  • System types: Combi, system, regular
  • Dimensions: 440 mm (w), 712 mm (h), 255 mm (b)
  • Price (for system boilers): 28 kW = £745; 38 kW = £1,033


Alpha E-tec models are the best system boilers for families on a budget. But don’t let that fool you; their 38 kW system boiler has a 15.1 litre/minute flow rate that can rival that of the toughest Worcester models.

This innovative combi boiler offers all the essential features, like smart thermostat compatibility, while being in the budget-friendly price range. These Alpha boilers are ideal for medium-sized homes, prioritising boiler longevity.

They have a stainless steel heat exchanger, allowing them to withstand high heat and preventing early corrosion. The zinc-plated expansion vessels are another top-class feature of this system boiler.

Plus, they are 93% energy-efficient – you definitely can’t go wrong with this system boiler!

Quick boiler summary

Viessmann Vitodens 100-W System Boiler

  • 94% energy rating
  • Starting at £1,025
  • Wi-Fi
  • LCD touchscreen
  • Hydrogen-ready boiler
  • Ideal for larger homes

Worcester Bosch 4000 System Boiler

  • 94% energy rating
  • Starting at £1,100
  • Intelligent filling technology
  • Wi-Fi
  • Thermostatic radiator valves
  • Ideal for larger homes

Worcester Bosch Greenstar i System Boiler

  • 94% energy rating
  • Starting at £1,150
  • Condensing technology
  • Top gas system boiler
  • Suitable for most home sizes

Vaillant ecoTEC Plus 624 System

  • 94% energy rating
  • Starting at £1,227
  • Condensing technology
  • Ultra quiet performance
  • Ideal for medium-sized homes

Alpha E-Tec System Boiler 

  • 93% energy rating
  • Starting at £745
  • The most popular system boilers for families on a budget
  • Combi boiler system
  • Stainless steel heat exchangers

Understanding System Boilers

  • Definition: A system boiler is a device used in homes to provide heating and hot water.
  • Best for: Medium- to large-sized homes, or those with higher hot water demands.

System boilers are synonymous with modern home heating, combining energy efficiency and reliability into one. While they are smaller than conventional boilers – which require a hot and cold water tank – they are bulkier than combi boilers.

System boilers heat central heating systems directly and produce hot water from their hot water cylinder which is usually installed in the attic. While they are in the higher boiler price bracket – ranging between £600 and £2,500 – you can’t put a price tag on reliability.

Many components work together to keep a system boiler functioning:

  • Heat exchanger
  • Combustion chamber
  • Expansion tank
  • Hot water cylinder
  • Pressure gauge

Advantages of system boilers

  • Heating efficiency: By preheating water and storing it in the storage cylinder, system boilers provide a steady supply of hot water, whereas combi boilers heat water on demand.
  • Bigger boiler systems: A system boiler supplies hot water to multiple bathrooms without compromising water pressure. They also have immersion systems, so if the power goes out, these units can still supply hot water.
  • Reduced heating bills: Storing hot water helps reduce energy bills and prevents the system boiler from running constantly.
  • Reduced carbon footprint: The best system boilers use less energy to generate heat, releasing fewer carbon emissions. They connect to solar panels more easily than other boiler models.
  • Less noise: A system boiler is a compact unit that omits less sound than conventional or combi boilers.
  • Fewer parts: System boilers have a third fewer components than combi boilers – and fewer components to repair or replace when systems break down.

Choosing The Right System Boiler For Your Home

All homeowners obviously want the best system boiler that money can buy. You’d assume that the higher the price tag, the better the boiler – but (it’s true) money isn’t everything!

Before you make a hasty decision, there are a couple of things to consider:

Home size

Assess the size of your home and the number of bathrooms you have. Larger homes with multiple bathrooms need bigger boiler systems to fulfil higher water demands; whereas smaller homes need a smaller central heating system.

Boiler size

Choosing the correct sized boiler is crucial. Boilers that are too small won’t provide enough heating, whilst too large a boiler will result in wasted heat and energy.

Energy rating

Opt for a system with high energy ratings to minimise energy bills and carbon emissions. Hydrogen-ready boilers are great future-proof heating systems to go for.

Fuel type

Consider fuel type costs and which are available in your area.


If you’re having a new system boiler installed, ensure that it is compatible with your existing heating system – this includes radiators, pipes, and controls.

Another thing to consider is whether or not it’s compatible with smart controls.

Boiler manufacturers

Opt for reputable boiler brands as they usually have boiler warranties in place; especially helpful when systems are faulty or break down.


Consider how much you want to spend on a new system boiler, weighing up running costs, annual servicing, and replacements.

It’s also advisable to get several boiler quotes from various suppliers. Factors to consider are boiler installation costs, price points, features, and boiler warranty comparisons.


Which system boiler is most efficient?

Condensing boilers are the most efficient system boilers on the market.

What brand of boiler is the best?

One boiler manufacturer may be ideal for one particular household while a different boiler brand is better for another. In general, Worcester Bosch, Vaillant, Viessmann or Ideal Logic system boilers are good options. 

Which is better: a regular or a system boiler?

In terms of energy ratings; a condensing system boiler is typically 90% – 95% efficient, whereas a non-condensing regular boiler is only 85% efficient.


Homeowners need to understand the basic functionality of a system boiler before they have a new one installed. Things like house size, lifestyle, fuel types and budget all play a major part when choosing the best system boiler for your home.Whether you opt for the popular Viessmann 100-W System Boiler with built-in Wi-Fi or the budget-friendly Alpha E-Tec model – speak to Eco Happy today. We’re your trusted boiler partner and will help you choose the best system for your home!

James Elston

Boiler Expert

James Elston is the top boiler replacement and heating expert at Eco Happy. He has over 20 years of experience in the industry, focusing on Gas Safe boiler installations and offering home-heating and energy-saving solutions to homeowners across the UK. From sourcing the most energy-efficient combi boiler to providing specialist heating advice, James ensures that Eco Happy maintains the highest standards and best customer service.

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