Introducing the Worcester Bosch Greenstar 4000

The Worcester Bosch Greenstar 4000 is a recent addition to Worcester Bosch’s efficient boiler range. It is designed as a direct replacement for the popular Greenstar i range. Available in combi and system boiler models, with outputs ranging from 12kW to 30kW, it’s ideal for small to medium-sized homes seeking energy-efficient, reliable heating.

Launched in 2021, the Greenstar 4000 combines modern design, quieter operation, and smart home compatibility. As the UK’s market leader in domestic boiler manufacturing, Worcester Bosch continues to raise the bar in home heating innovation.

At WarmZilla, we’re proud to offer great value on the full Worcester Bosch Greenstar 4000 range — including an exclusive package on the 30kW combi model. Use our free online tool to get a personalised 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 47,000 reviews, and ranked number 3 of 7 in the Boiler Manufacturer category, Worcester Bosch boilers are renowned for their reliability and efficiency.

In the 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

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 Greenstar 4000 became the direct replacement for the Greenstar i range, which is currently Worcester’s bestseller.

Introduction to the 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 remains 5* by undergoing intense transport tests to ensure 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, 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 12kW, 15kW, 18kW, 21kW, 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. 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 Worcester Bosch Greenstar 4000.

Information Table

** 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
• SimpleSwitch

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.

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.

If you’re considering a system boiler, remember it requires a separate hot water storage tank, usually tucked away in an airing cupboard. This makes it better suited for homes with more space and higher hot water demands, like those with multiple bathrooms.

Combi boilers, on the other hand, are perfect for smaller homes and flats. They don’t need a tank. Instead, they heat water directly from the mains, delivering instant hot water on demand.

The Worcester Bosch Greenstar 4000 is available in both combi and system models. It’s compact enough to fit inside a standard kitchen cupboard and offers high flow rates of up to 12.3 litres per minute, ideal for quick, powerful hot water to your taps and showers.

Every model includes simple controls, a clear LCD display, and built-in frost protection for added reliability in colder months.

What kW output do I need for my home?

Choosing the correct boiler size (kW output) is essential for efficient heating and hot water. If your boiler is too small, it may struggle to meet your home’s demands, overworking and increasing energy bills. You could be wasting money on unnecessary capacity if it’s too powerful.

So, what size boiler do you need? The ideal kW output depends on several factors, including the number of radiators, bathrooms, insulation, and your hot water usage habits.

To make things easier, WarmZilla offers a quick online boiler survey that calculates the perfect boiler for your home. Just answer a few simple questions about your property, and our intelligent tool will recommend the best models based on your needs.

You can also speak to our friendly team via live chat or by calling 0333 577 9090, especially if you’re planning a home extension or adding a bathroom and want to check your boiler can handle the extra demand.

Scroll down to view our boiler size guide or check out our related blogs to learn more about what kW means and the factors that affect your boiler choice.

Combi Boiler kW Size Guide

System Boiler kW Size Guide