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Worcester Bosch Greenstar 4000 Boiler Review (2021 Model)

The latest and greatest boiler from the heating giants, Worcester Bosch. Packed with tech, a compact size, and a sleek design. Is there anything the Greenstar 4000 boiler can't do? Here's our review.

Worcester Bosch has been one of the best selling boiler brands in the UK boiler market for decades, earning a solid reputation among both installers and customers and holding the Which? Best Buy Award for 10 years and counting.

10 years = a whole decade

The Worcester Bosch Greenstar 4000 series is one of the brands latest innovations, set to replace their far-best-ever-selling boiler, the Greenstar i

Worcester Bosch Greenstar 4000 Combi BoilerOn May 17th, 2021, Worcester are simultaneously launching the new 4000 combi (to replace the Greenstar i) and the new 4000 system boiler range which will replace the equally successful Greenstar i system range.

A double delight for boiler enthusiasts.

Worcester Bosch Greenstar 4000 Boiler Review 

In this 4000 boiler review, we've scored the 4000 in 4 key areas, including:

  • Reliability:
    5/5 Stars ⭐⭐⭐⭐⭐
  • Performance:
    4/5 Stars ⭐⭐⭐⭐
  • Warranty:
    5/5 Stars ⭐⭐⭐⭐⭐
  • Price:
    4/5 Stars ⭐⭐⭐⭐

Designed to sit between the 2000 and 8000 series boilers, the 4000 is the brand's mid-range boiler. 

The 4000 is offered in multiple sizes including 25kW and 30kW, all coming with an impressive 10-year guarantee for parts and labour (when purchased via Heatable).

Want to learn more about Worcester Bosch? Check out our complete guide to the brand.

Let’s take an in-depth dive into the 4000 and everything that it has to offer…..

Main features of the Worcester Bosch 4000 Boiler

  • Worcester Bosch’s mid-range model
  • Designed to have a quieter operation than the Greenstar i
  • Compatible with all Worcester Bosch controls and third party controllers such as Hive, Nest, tado etc.
  • Ideal for small and medium sized homes 
  • Easy access with removable side panels
  • 10-year guarantee on parts and labour (when purchased via Heatable) 
  • ErP rating 94%: A-rated
  • Dimensions: 710 x 400 x 310

Reliability: 5/5

Worcester Bosch Greenstar 4000 Reliability

The Worcester Bosch 4000 combi boiler has replaced the Worcester Bosch Greenstar i, the brands best-selling boiler model and just like the previous version, it offers incredible value for money and reliability. 

Trustpilot Reviews 

For illustration, on TrustPilot, Worcester Bosch has racked up an incredible amount of reviews. As of May 2021, over 17,000 customers left a review. An incredible feat. 

Worcester Bosch Reviews

The brand has an average rating of 4.7 stars out of 5, a huge achievement for a brand selling so many boilers, a testament to their reliability and amazing aftercare. 

Moreover, in our article ranking the best boiler manufacturers, the brand was rated as offering the best combi boilers of 2021;  so, this is certainly a boiler brand with credibility.


If you are left wondering whether to choose between Viessmann and Worcester, check out our recent comparison between the two brands.

Which? Boiler Survey Results 

Worcester 4000 Which Best BuyWorcester have carried the Which? Best Buy Award for over 10 years now and being based in the UK also means parts are very easy to obtain and their customer service is reliable. 

In fact, in the most recent annual boiler survey feedback was gathered from over 100 installers and received several high 5-star ratings the consumer choice organisation considers most important to consumers, including full marks for their build quality and availability of parts and spares.

Performance: 5/5

Worcester Bosch 4000 Performance Review

Worcester Bosch 4000 Combi Boiler Power Outputs: 

Worcester Bosch 4000 Power Options

The Greenstar 4000 combi boiler range is available in the following sizes (power outputs):

  • 25kW
  • 30kW

The 25kW combi boiler has a heat output of 25kW and a flow rate of 10.5 l/min, making it suitable for small properties and flats that may have limited hot water demands. 

The 30kW has an additional 5kW of power and a flow rate of 12.3 l/min making it suitable for medium sized properties with higher hot water demands.

Want to know which boiler power is right for your home? Check out our boiler sizing guide

You can check the latest deals on Worcester Bosch boilers here, and see how the brand compared to another market leader in our Worcester Bosch vs Vaillant Boilers comparison

Worcester Bosch Greenstar 4000 System Boiler

The 4000 range is also offered as a system boiler, this is a different type of boiler, ideal for homes with multiple bathrooms and hot water outlets.


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

Which 4000 model is right for your home?

If you’re curious about the size boiler that’s most suitable for your home, use our free tool. It will do all the hard work for you, calculate the boiler you require and provide a fixed price. 

Efficiency of the Worcester Bosch 4000

Worcester Bosch 4000 Efficiency

The Worcester Bosch Greenstar 4000 is accredited as A-rated for energy efficiency, with an incredible 94% efficiency.

Looking for a more budget-friendly boiler? Check out our review of the Worcester Bosch 2000, or if you want the latest and greatest check out the Worcester Bosch 8000

Want to know how these boilers compare, check out our 2000 vs 4000 vs 8000

Learn all about combi boilers in our what is a combi boiler guide and see how the brand fared against Baxi in our Worcester Bosch vs Baxi comparison.

Controls & Features of the Greenstar 4000

Worcester Bosch 4000 Features


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

Upgraded Exterior 

The design language of the new 4000 series is carried over from the 2000 and 8000 range.

Curved edge casings and the digital display is a nice move away from the boring square boxes of old.

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

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

Just like the Greenstar i range, the Greenstar 4000 range is 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. 

It will also alert you if the boiler is losing too much pressure, allowing you avoid unnecessary engineer callouts. 

...note: this feature is only available with the combi boiler and not the 4000 system boiler. 

The Worcester Bosch 4000 is also compatible with many of Worcester’s other controls, including: 

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

System Filter Compatibility 

Building regulations now stipulate a system filter is fitted with all new installations. 

The 4000 series will be compatible with the Worcester Greenstar System filter and third party filters.

However, to access the maximum guarantee lengths, Worcester stipulates you must install their filter to benefit from the increased cover.

Warranty: 5/5

Worcester Bosch 4000 Warranty

Worcester Bosch Greenstar 4000 Guarantee

An important consideration when buying a new boiler is the warranty or in the case of Worcester Bosch the far superior guarantee. 

...What’s the difference between a warranty and a guarantee? 

Essentially, a guarantee is an agreement from the brand that they will attend your property and repair or replace the boiler within a reasonable timeframe. 

Worcester Bosch 4000 10 Year Guarantee

Most other boiler manufacturers only offer a warranty as standard, this is an agreement to investigate the problem, but is not an unconditional agreement to fix or repair it for free.

With the 4000 range, you will be securing an industry leading ten year guarantee on parts and labour (when purchased via Heatable), which offers you the peace of mind for the next decade. 

Price Point: 4/5

Worcester Bosch 4000 Cost

Worcester Bosch 4000 Combi Boiler Costs

The 4000 is a mid-range boiler offered by a premium boiler brand, so although it’s not their most expensive boiler, it’s not the cheapest boiler you’ll find either. But that’s the price you pay for excellent quality and aftercare. 

The exact costs of the boiler (including Gas Safe installation) may vary depending on your type of property, hot water demands and a whole host of other facts.

So, to make it easy, we have designed a quick questionnaire that will give you an instant fixed price. It takes about 60 seconds to complete.

Worcester Bosch Greenstar i vs Greenstar 4000 - What’s the difference? 

The Worcester Bosch Greenstar i was Worcester’s mid-range boiler and their best selling combi boiler range, which has now been replaced by the better looking Worcester Bosch Greenstar 4000. 

So what’s the difference and what’s changed? 

The Worcester Bosch 4000 offers everything the i range did, but with some major improvements. 

The new 4000 range has a quieter operation and provides a higher hot water output. 

  Greenstar i Greenstar 4000
Dimensions H 710
W 400
D 330
H 710
W 400
D 310
Flow Rates 25kW - 10l/min 25kW - 10.2l/min
LCD Display Yes Yes
Frost Protection Yes Yes

As you can see in the above comparison table, there are many similarities between the two models. The 4000 does have smaller dimensions thanks to it’s new, sleek design, allowing it to more snuggly fit into tight spaces, including kitchen cupboards. 

The 4000 also offers a higher flow rate of 10.2 litres a minute, meaning it provides faster hot water to your water outlets. Both boiler models have easy-to-use controls, an easy-to-read LCD digital display screen, and built-in frost protection to guard against freezing during the colder months of the year. 

Our Verdict on the 4000

Greenstar 4000 Verdict

The Worcester Bosch Greenstar 4000 is a mid-range model offering all of the most essential features and contemporary exterior at a competitive price. 

The 4000 is replacing Worcester’s best selling Greenstar i range and offers all the same features, but has some additional perks including a more compact design for a streamlined installation into your standard kitchen cupboard. 


It also offers a higher flow rate of 10.2 litres a minute which means that it provides faster hot water to your taps and showers. 

Greenstar 4000 Review Handover

The 4000 also benefits from the brand's most recent innovations such as the intelligent filling system, frost protection, ECO mode and wireless connectivity. 

The boiler's exterior is also a huge improvement offering homeowners not only a boiler that works great, but one that looks great. The design language of the new 4000 series is carried over from the 2000 and 8000 range. Curved edge casings and  digital displays are a nice move away from the old boiler models. 

Check the latest price of the Worcester Bosch 4000 boiler

Finally, with the brand winning the Which? Best Buy Award for 10 years in a row, receiving extremely high TrustPilot reviews and offering an industry leading 10 year guarantee (not just a warranty), we fail to see any rivals catching up anytime soon.

Should you buy it? If you're looking for a reliable boiler from a brand that’s been winning awards for the past 10 years, certainly. 

Worcester Bosch Boilers

Looking for the best deal on a Worcester Bosch 4000? 

If so, get your new boiler installed with Heatable, here’s why: 

  • Gas Safe installation within 24 hours
  • Thousands of happy customers – an average score of 4.9 on Trustpilot (that’s better than the market leader).
  • Price match guarantee – if you find a cheaper quote, we will match (must be like for like)
  • Multiple payment options - interest free available
  • 10 year guarantee
  • Fixed price guarantee – no hidden costs
  • Save your quote until later

Use this clickable form to get a fixed price on the screen instantly.

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Heatable is registered in England and Wales No. 08804726 (VAT No. GB205805920 ). Trading address is 1 Station Road, Great Sankey, Warrington, Cheshire, WA5 1RH. Heatable acts as a credit broker (not as a lender) and offers credit products through a panel of lenders. Heatable is authorised and regulated by the Financial Conduct Authority (reference no. 805259).

[1] Price based on a like for like combi swap in a 2 bed, 1 bathroom terraced home with a standard flue

[*] Installation dates are subject to installer availability

[ยน] only available on combi boiler installations

Financial Support: If you are in receipt of certain benefits, you may be entitled to claim a free boiler grant.