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Last updated: 15th September, 2022


Worcester Bosch Greenstar 4000 Combi Boiler Review

Worcester Bosch Greenstar 4000 Combi Boiler Review

An in-depth review of the Worcester Bosch Greenstar 4000 Combi boiler, taking a look at its best features, efficiency, dimensions, ease of use and price.

In this boiler review, we will be exploring the Worcester Bosch Greenstar 4000 combi boiler, taking a look at its features, efficiency, price and accreditations in detail.

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Brand Overview: Worcester Bosch

To start, let’s find out a little bit about the manufacturer Worcester Bosch...

Keeping UK homes warm since 1962, Worcester Bosch is committed to delivering the highest standard of heating.

With a wide range of high quality products that use innovative technologies, you can be sure that Worcester Bosch boilers will integrate seamlessly into your home or business premises, saving you money on your heating bills thanks to their high efficiency ratings.

It’s no wonder Worcester Bosch is an eleven time winner of the Which? Best Buy award, with Which? claiming “Worcester Bosch performs so consistently well in our annual reliability surveys that its name is synonymous with dependability.” 

Worcester Bosch Greenstar 4000 Combi

According to Worcester Bosch, the Greenstar 4000 has been built on all of the tried, tested and much-loved features of the Greenstar i, making the 4000 instantly familiar and yet totally transformed.

The Greenstar 4000 is ideal for small to medium sized homes with one bathroom. It features a modern new design, an easy to use full colour text display and it’s quiet too. 

The Greenstar 4000 has a wide power range to meet all of your heating and hot water needs, whilst doing so efficiently.

Worcester Bosch Greenstar 4000 Combi Boiler Features

  • Available in 25kW and 30kW with iHeat

  • Aluminium heat exchanger

  • A-rated for efficiency (91%)

  • Hot water flow rate 10.2 / 12.3 litres per minute

  • Dimensions W 400mm, D 310mm, H 724mm

  • Easy-to-use full colour display

  • Quiet Mark Certified

  • Built-in frost protection

  • 10 Year Warranty with iHeat

The Features in More Detail

Worcester Bosch 4000 Combi Power Output and Hot Water Flow Rate

At iHeat, the Worcester Bosch Greenstar 4000 Combi is available in two heat output sizes: 25kW and 30kW.

Power Output







Up to 10

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The Worcester Bosch Greenstar 4000 25kW is perfect for small homes or flats with one to two bedrooms, one bathroom and up to ten radiators. 

With a hot water flow rate of 10.2 litres per minute, this boiler can provide instantaneous hot water to households with a smaller demand.

Power Output







Up to 15

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The Worcester Bosch Greenstar 4000 30kW is best suited for mid-range homes with between three to four bedrooms, multiple bathrooms and up to fifteen radiators. 

With a hot water flow rate of 12.3 litres per minute, slightly higher demands for instantaneous hot water can be met.

Worcester Bosch 4000 Combi Aluminium Heat Exchanger

When looking for a new boiler, few people think to actually research the internal components, however, this can be a mistake as the quality of materials used can significantly impact the effectiveness of a boiler and whether or not it will stand the test of time.

The Ideal Logic+ uses an aluminium heat exchanger, which has been used in millions of boilers across Europe since the 1970s.

The benefits of an aluminium heat exchanger include:

Very High Thermal Conductivity

Aluminium has a very high thermal conductivity (237W/m²/K), meaning it has a strong ability to transfer heat. 

Because of this high thermal conductivity, the heat exchanger itself requires less surface area, meaning the boiler can be more lightweight and compact.

Quiet Operation

Thanks to the large waterways in an aluminium heat exchanger, the water velocity can be reduced, in turn reducing the amount of noise. 

This boiler was even awarded the Quiet Mark for such low noise levels.

Corrosion Resistance

On contact with water or oxygen, a non-porous protective layer of aluminium oxide is formed naturally, called alumina (or the passivation layer).

This chemical reaction contributes to the heat exchangers being highly resistant to the corrosion effects of condensate during operation.

Aluminium vs Stainless Steel Heat Exchangers

A key thing to keep in mind, however, is that stainless steel heat exchangers are more desirable than aluminium due to their better corrosion resistance, durability and reliability. 

Unfortunately, one of the biggest complaints about the Worcester Bosch range is the company’s use of aluminium heat exchangers compared to competitors such as Viessmann who use stainless steel heat exchangers.

Worcester Bosch 4000 Combi Efficiency

The efficiency of the Worcester Bosch Greenstar 4000 combi is what makes it stand out from the crowd.

Thanks to its A-rated 91% energy efficiency, you can make incredible savings on your heating bills and reduce your carbon emissions- all without changing your current consumption.

Unsurprisingly, this boiler meets all ErP (Energy-related Products) regulations, meaning it has been carefully designed with energy efficiency in mind.

Worcester Bosch 4000 Combi Compact Dimensions

When shopping for a boiler, an important thing to check is the dimensions of the unit so you can be sure it will fit in the location you wish to have it installed.

Fortunately, the Worcester Bosch Greenstar 4000 has compact dimensions of W 400mm, D 310mm, H 724mm, meaning it can fit inside standard kitchen cupboards, helping you to save space elsewhere in your home.

(Always make sure to measure the area you wish to have it installed to be sure your desired boiler model will fit.)

Worcester Bosch 4000 Combi Easy-to-Use Full Colour Display

The modern new design comes with an easy to use colour display, making it a lot easier to read and notice any alert messages.

This means quick fixes such as topping up your boiler pressure are made a lot simpler.

Worcester Bosch 4000 Combi Warranty

If you get a Worcester Bosch 4000 Greenstar Combi boiler installed with iHeat you can get a huge 10 year warranty on parts and labour, so you can rest easy knowing you’re covered in the unlikely event of something going wrong.

Worcester Bosch 4000 Combi Awards and Accreditations

Which Best Buy Gas Combi Boilers

The Greenstar 4000 combi boiler was recognised as a Which? Best Buy Gas Combi Boiler in 2019, 2020 and 2021.

Which? Best Buy is awarded to products which have satisfied or exceeded specific criteria based on the results of rigorous comparative tests and analysis carried out by Which?

Quiet Mark

As mentioned earlier, this model received the Quiet Mark, a certification that assesses products for their solutions to unwanted noise. 

A quieter operation means no more noisy bangs or rumbling from your boiler.

Worcester Bosch 4000 Combi Boiler Price

Worcester Bosch has a wide range of budget, mid-range and premium boilers available. 

The Greenstar 4000 price falls under the mid-range, between the Greenstar 2000 and Greenstar 8000, so it’s not the cheapest, but it's also not the most expensive boiler on the market.

Although there are cheaper options on the market, the Worcester Bosch price tag is slightly higher than other boiler manufacturers for a number of good reasons.

Why Worcester Bosch Boilers are Worth the Price:

  • Firstly, they offer 10-year guarantees (not warranties). Guarantees typically cover the whole product and Worcester Bosch won't charge you for a guarantee call out visit providing that your boiler is serviced annually.

  • Winner of multiple Which? Best Buy awards

  • High TrustPilot ratings

  • Huge brand name thanks to reliability

  • Made in the UK

Opting for the cheapest boiler on the market could actually end up costing you more in the long run.

The exact price of the boiler depends on the type and size of property you have, your demand for hot water and the installation costs.

To make it simple, we have made a quick questionnaire that can give you an instant fixed quote on a Worcester Bosch 4000 Combi boiler.

Our fixed price includes both the new combi boiler and complete installation from our Gas Safe engineers, delivering the full package.

What are the Key Differences Between the Greenstar Boiler Range?

The biggest difference between the Greenstar 2000 and Greenstar 4000 is the number of innovative features the Greenstar 4000 has to offer.

It features wireless connectivity, meaning you can control the boiler remotely via smart thermostats such as the Google Nest, making controlling your heating more convenient.

The 4000 also offers a ‘Quick Tap’ water saving function to help you reduce water waste.

The key difference between the Greenstar Style 8000 is the availability of power outputs.

The 8000 is more powerful and designed for larger homes that require greater heating and hot water.

The Greenstar 4000 is available in outputs between 25kW and 30kW, whereas the Greenstar 8000 is available in power outputs between 30kW and 50kW, hence why it is more expensive 

Our Verdict

The Worcester Bosch Greenstar 4000 Combi boiler is a fantastic model with a range of highly efficient features for an affordable price, helping you to make great savings all around.

Its upgraded exterior has a sleek design with curved edge casings. Available in both black and white also makes it incredibly stylish, suitable for any home.

As a winner of the Which? Best Buy award for three years running, there’s no doubt this boiler can provide you with an effective and reliable heating solution.

Get a free fixed quote on a brand new Worcester Bosch Greenstar 4000 Combi plus installation from a Gas Safe registered engineer today!

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Article by
Stephen Day | Co-founder
Gas Safe registered and FGAS certified engineer with over 20 years experience in the heating and cooling industry.