Introducing the Worcester Bosch Greenstar 4000 Re April 23, 2021

Introducing the Worcester Bosch Greenstar 4000


Introducing the Worcester Bosch Greenstar 4000 series, the direct replacement for the Greenstar i range of Worcester Bosch boilers.

Named the ‘UK’s market leader in domestic boiler manufacturing’, Worcester Bosch offers a range of Combi, System, and Regular (Heat Only) Boilers.

The Worcester Bosch Greenstar 4000 is available as a combi boiler and system boiler with outputs between 12kW and 30kW available. The Worcester Bosch Greenstar 4000 was launched on May 17th, 2021.

WarmZilla offers great prices on the Worcester Bosch 4000 boiler, including the package below on the most popular 30kW model. For a bespoke boiler quote based on your home just click on the image below and get an online boiler quote in minutes.

According to their website, Worcester Bosch’ mission statements says,


“At the turn of the tap or the tap of an app, our boilers bring physical comfort, but they are also a wellspring of emotional warmth and enhanced wellbeing. Hidden in a cupboard, living on a kitchen wall or sitting in an airing cupboard, our boilers get on with warming lives so that people can get on with living and enjoying life”.

If you’re looking for some information on the exciting Greenstar 4000, grab your cup of tea and biscuits at the ready, and let’s get into it. 

Brand Overview of Worcester Bosch

Formed in 1962, Worcester started off as a small business in the small village of St. Martins Gate. The company was then renamed in 1992 to what we know today as Worcester Bosch, due to an acquisition by Robert Bosch, and are now known as the market leaders of boilers in the UK. 

With a trust rating of 4.6 on Trustpilot and over 23,000 reviews, and ranked number 3 of 7 in the Boiler Manufacturer category, Worcester Bosch boilers are renowned for their reliability and efficiency. 

In the 2020 Which? Best Buy annual Best Boiler Brand survey, Worcester bosch received an overall score of 79%. Over 7,500 boiler owners and 153 boiler engineers from Which? Trusted Traders were asked to score Worcester Bosch boilers on;

  • Reliability 
  • Customer Score
  • Engineer recommendation 
  • Build quality
  • Availability of parts and spares 
  • Ease of fixing a common fault 
  • Ease of servicing 

2020 Which? Best Buy Best Boiler Brand Survey Results 

Overall Score79%
Reliability 5 stars
Customer Score 5 stars
Engineer recommendation4 stars
Build quality4 stars
Availability of parts and spares 5 stars
Ease of fixing a common fault2 stars
Ease of servicing 3 stars

Worcester Bosch say:

“Yes, boilers are our everyday, and heating and hot water our world, but generating and sharing warmth is our reason for being. It’s the value we create and the joy we bring. It’s our calling”.

Now you know about the background of Worcester Bosch as a company, let’s see why the new Greenstar 4000 will become the direct replacement for the Greenstar i range, which is currently Worcester’s bestseller.

Introduction to the NEW Worcester Bosch Greenstar 4000

In efforts to become more planet-friendly, the original polystyrene packaging used to package Worcester Bosch boilers has been replaced with recyclable cardboard. They have also ensured that all plastic packaging has been replaced with compostable bags which can be used in your garden or as a food waste bin. Although their packaging has been changed, their delivery still remains 5* by undergoing intense transport tests to make sure that your boiler is still protected and the new packaging is robust and keeps your boiler safe.

Based on the design of the famous, best-selling boiler on the market, the Worcester Bosch Greenstar i, Worcester Bosch have created a new and improved version, raising the bar with ease and speed of installation, commissioning, and servicing. The exterior of the 4000 series is very similar to that of the Worcester Bosch 8000 Life and Style boiler range, but it is significantly cheaper.

This means you are getting all the great features and benefits of the Worcester Bosch Greenstar i, but with a little added spice. 

The Worcester Bosch 4000 will be available as a combi boiler with outputs of 25kW and 30kW available with a flow rate of up to 12.3 l/min, and a system boiler in 12kW15kW18kW21kW, and 24kW

Worcester Bosch has designed the 4000 series as a ‘SimpleSwitch’ for customers who have an existing Greenstar i, i Junior or Si boiler, as the brand new Greenstar 4000 physically fits within the i footprint of these boiler ranges.

The Greenstar 4000 has a quieter operation and increased hot water efficiency compared to their Greenstar i range. The Greenstar 4000 has frontal access to all key components for easy installation and any future servicing or maintenance.  The Worcester Bosch Greenstar 4000 has also been designed to be compact and lightweight, meaning that it can be fitted neatly inside your standard kitchen cupboard, out of sight, out of mind. 

Whilst the UK Government continues to increase the amount of green fuels being introduced, such as bio-methane and hydrogen, Worcester Bosch customers can be confident that their new Worcester Bosch Greenstar 4000 gas boiler will run for its lifespan.

Martyn Bridges, Director of Technical Communication and Product Management at Worcester Bosch has said that all Worcester Bosch Greenstar condensing gas boilers manufactured since 2000 can accept a hydrogen blend of up to 20%.

Bridges also said that “the fact that Worcester’s boiler can already accept a blend of up to 20% is further evidence why injecting green fuels such as bio-methane and hydrogen into the UK gas grid is a positive step towards the wider implementation of these new, carbon-free fuels”.

Worcester Bosch is involved in multiple trials with hydrogen gas, including one at Keele University. For the last 18 months, Worcester Bosch has had 150 boilers that have been running up to a 20% hydrogen blend. They are now trialling this in 670 homes in Gateshead.

Worcester Bosch has continued to increase the use of green gases, launching the Hy4Heat programme that is currently trialling 100% hydrogen boilers that are running in specially-built demonstration houses in Northumberland.

More importantly, Worcester Bosch has made significant progress with prototypes and testing, developing hydrogen ready boilers. These hydrogen boilers look almost identical to your typical everyday gas boiler and they are installed in pretty much the same way.

Similar to gas boilers, hydrogen boilers will be connected to the gas mains and then the hydrogen or natural gases will be fed to the boiler from there. 

There are a few small differences when it comes to the internal components of the new hydrogen boilers, such as a hydrogen-ready flame detector and burner.

It is not possible to buy a 100% hydrogen-ready boiler just yet and until there is a reliable supply of hydrogen gas, it wouldn’t make much sense to have one yet anyway.

Below you will find a table with all the key information regarding the brand new Worcester Bosch Greenstar 4000. 

Information Table

ModelGreenstar 4000 Combi

Flow rate at the hot water tap
(35°C rise)

10.2 l/min (25kW) and 12.3 l/min (30kW)
Flow rate at the hot water tap
(40°C rise)
9 l/min (25kW) and 10.8 l/min (30kW)

Output kW to central heating 
(model dependant)

3kW – 24kW 
Maximum flue length (60/100mm)12m
Intelligent Filling SystemOptional accessory 
Condensing in domestic hot water (combi)Yes
ErP ‘A+’ rating with weather compensation control*Yes
Intelligent controls**Yes

** Additional accessories required for system boiler range

Controls and Features included

The Worcester Bosch Greenstar 4000 is compatible with the following controls:

  • MT20
  • Comfort+
  • Comfort+ Stats RF
  • Comfort+ | RF 
  • Comfort+ || RF 
  • Easy Controls 

Since the 4000 is set to replace the Greenstar i range, Worcester has ‘SimpleSwitch’, which means it will fit within the Greenstar i footprint of any of the condensing boilers within that range. This is ideal for previous customers that are wanting an upgrade with limited disruption. 

Upgraded Exterior 
The new Greenstar 4000’s design is based on the sleek design of the Worcester Bosch Greenstar 2000 and Greenstar 8000. Curved edge casings and the digital display is a nice move away from the boring square boxes of old.

The new user-friendly LCD display upgrade and easy to use push control buttons are also a huge improvement. The Greenstar 4000 also features wireless connectivity, allowing you to connect the boiler to Bosch EasyControl and control the boiler remotely from your smartphone or other electronic devices.

Easy Access Side Panels 
The new design of the 4000 also means the boiler is easier than ever to gain access to, allowing engineers to service and repair your boiler with minimal disruption. 

Intelligent Filling System
Similar to the Greenstar i range, the Greenstar 4000 range is also compatible with Worcester’s intelligent filling system. 

This system uses software that is able to maintain your boiler’s pressure at its optimum level. If the pressure drops, the internal filling valve will jump into action and automatically refill the system and turn back off once done.

Comparison table

Now we know a little more about the background of Worcester Bosch’s history and we’re more clued up on the Worcester Bosch Greenstar 4000, let’s get into the nitty-gritty. 

We know that the 4000 is based on the DNA of the Greenstar i but with a little more to offer, such as quieter operation and increased hot water. But let’s look into how different these boiler models really are. We have created a table below to show the difference between the Greenstar i and 4000 combi’s and the system boiler range. 

If you are interested in reading more about the Worcester Bosch Greenstar 25i / 30i, we have a blog just waiting for you.  

Key Factors Information Table- Combi boiler range 

The Worcester Bosch 4000 combi boiler range will be available in the following outputs: 25kW and 30kW.

MakeWorcester Bosch

Worcester Bosch        

Worcester Bosch Worcester Bosch 
ModelGreenstar 25i Combi Gas Boiler                  Greenstar 4000 25kW Combi Gas Boiler Greenstar 30i Combi Gas BoilerGreenstar 4000 30kW Combi Gas Boiler 
Condensing Boiler Yes


LPG CompatibleYesYesYesYes
Standard Guarantee 5 years Up to 10 years5 years Up to 10 years
Central Heating Output25kW25kW30kW30kW
Mounting YesYesYesYes
Flow Rate 9 l/min10.2 l/min12.3 l/min12.3 l/min

Dimensions (mm)

710 x 400 x 330

710 x 400 x 310710 x 400 x 330710 x 400 x 310

Key Factors Information Table- System boiler range 

The Worcester Bosch 4000 system boiler range will be available in the following output options: 12kW, 15kW, 18kW, 21kW and 24kW. 

MakeWorcester BoschWorcester BoschWorcester        BoschWorcester Bosch
ModelGreenstar 21i System Gas Boiler Greenstar 4000 21kW System Gas Boiler Greenstar 24i System Gas BoilerGreenstar 4000 24kW Combi Gas Boiler 
Condensing Boiler YesYesYesYes
LPG CompatibleYesYesYesYes
Standard GuaranteeUp to 7 years Up to 10 yearsUp to 7 years Up to 10 years
Central Heating Output21.6kW21kW24.6kW24kW
Mounting Wall Mounted Wall Mounted Wall Mounted Wall Mounted 
Flow Rate N/AN/AN/AN/A 
Dimensions (mm)
710 x 400 x 330710 x 400 x 310710 x 400 x 330710 x 400 x 310

It is important to note when purchasing a new or replacement system boiler, that you will need to accommodate for an additional hot water storage tank, typically located in an airing cupboard. Similar to regular boilers, system boilers are not ideal for homes with limited space. However, if space is not an issue in your home, then a system boiler could be a perfect choice, especially if you have a high demand for instant hot water.

This is due to the fact that system boilers are able to store hot water, ready to be used when needed. Unlike a combi boiler, with a system boiler, the hot water that is heating in the boiler unit is transferred into a hot water storage tank for later use.

On the other hand, combi boilers are ideal for smaller homes with limited space, such as flats or small apartments. Combi boilers (or combination boilers as some may call them) are ideal for those who need instant hot water on demand. This is because they are fed cold water directly from the mains, this cold water is then heated in the boiler unit itself and distributed where needed. If you are interested in more information on how combi boilers work, we’ve got this covered, don’t worry!

As you can see from the table below, there are not many other differences in regards to the key factors, however, the brand new Greenstar 4000 boiler unit has been designed to be more compact, for a neater installation into your standard kitchen cupboard.

The combi boiler options also offer a higher flow rate of 10.2 and 12.3 litres a minute which means that it provides faster hot water to your taps and showers.

All boiler models have easy-to-use controls, an easy-to-read LCD digital display screen, and built-in frost protection for extra peace of mind during the colder months. 

What kW output do I need for my home?

It’s important to choose the correct kW output boiler for you home, as choosing a boiler that it not designed to reach the demands for central heating in your home could lead to your boiler being over working, resulting in spending more money on heating your home. Visa-versa, if you get a boiler that has a kW output which is for homes larger than yours, then you could be wasting money.

The answer to ‘what size kW boiler do I need?’ is a bit more complicated as it depends on a few different factors – but don’t worry, we will answer those questions for you and get you up to speed on the perfect boiler size for you.

It’s worth noting that if you complete the WarmZilla Survey, then you don’t need to know what size kW boiler you need because our clever system calculates your water usage and heating requirements and supplies you with a list of boilers suitable for you.

If you ever want to talk with someone about your selection, then you can use our live chat or give us a call on 0333 577 9090. You may be thinking about adding an extension or additional bath/shower and like some advice on the additional power your boiler would need to provide adequate heating.

We have inserted a table below to help you see which kW output boiler is best suited to your home. If you are interested in learning about what other factors may affect the kW output needed for your home, we have a separate blog on this. We also have a blog that covers what kW means when it comes to your boiler. So make sure you check that blog out too. 

Combi Boiler kW Size Guide

No of bedrooms and bathroomsPoorly insulated propertyModerately insulated propertyWell insulated property
1 bed + 1 bath20kW20kW18kW
2 bed + 1 bath20kW20kW18kW
2 bed + 2 bath24kW20kW20kW
3 bed + 1 bath28kW26kW24kW
3 bed + 2 bath28kW28kW24kW
4 bed + 1 bath30kW30kW28kW
4 bed + 2 bath32kW32kW30kW
5 bed + 2 bath40kW35kW30kW

System Boiler kW Size Guide

No of bedrooms and bathroomsPoorly insulated propertyModerately insulated propertyWell insulated property
1 bed8kW7kW5kW
2 bed8kW7kW6kW
3 bed10kW9kW6kW
4 bed12kW10kW7kW
5 bed15kW12kW9kW
6+ bed18kW15kW12kW

*The WarmZilla Worcester Bosch 4000 Package includes an exclusive 12-year guarantee, 10 years provided by the manufacturer and 2 years provided by WarmZilla. More info is available on the WarmZilla T&C pages.

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