Worcester Bosch Greenstar 4000 Combi Boiler Review

In the ever-evolving world of home heating, Worcester Bosch has remained a steadfast choice for homeowners and professionals alike. Earning accolades such as the Which? Best Buy Award for a remarkable decade. The Worcester brand has solidified its status as a trusted name in the UK’s boiler market. But now, a new star is shining in the Worcester Bosch constellation…and it’s the Greenstar 4000. In this honest review, we will explore this innovative combi boiler, examining its features, reliability, performance, energy efficiency, warranty, and price point to help you make an informed decision.

Controls and Features of the Worcester Bosch Greenstar 4000

The Greenstar 4000 is positioned as the classic mid-range boiler within the Worcester Bosch portfolio. It sits between the 2000 and the 8000 models. Available in 25kW and 30kW, this boiler offers a generous 10-year guarantee for parts and labour when installed by Worcester accredited installers such as Expert Heat.

The 4000 range introduces several noteworthy features and improvements. It is designed to be a seamless replacement for the Greenstar i range, offering compatibility with the existing boiler footprint. This makes it an ideal choice for those looking to upgrade their existing Worcester Bosch boiler with minimal disruption.

The Worcester 4000 features upgraded exterior design, with curved edge casings and a digital display, adding a touch of modern aesthetics to your heating setup. The LCD display is user-friendly and enhances the overall control experience. The boiler also supports wireless connectivity, allowing remote control via a smartphone when combined with Worcester Bosch Easy Control smart thermostat.

Worcester Bosch A-rated Greenstar 4000 condensing combination boiler

Access to the Greenstar 4000 is easier than ever with removable side panels, simplifying service and maintenance. Also available with the Worcester Bosch intelligent filling system, which maintains the optimal pressure in the heating system, automatically refilling it when necessary and alerting you to pressure issues.

Pre heat – In pre heat mode, the boiler will pre heat the the hot water plate heat exchanger to reduce the delivery time of hot water to the tap.

Eco – Eco mode is an energy saving feature which turns off pre heat.

Quick tap – when the boiler is in eco mode you can use the quick tap function. This is designed to save water and can save up to 3.5 L/min.


Worcester Bosch Greenstar 4000 digital control displaysmart thermostats to control from your phone

Reliability: 5/5 Stars

Reliability is the cornerstone of the Greenstar 4000. The Worcester Bosch brand has consistently earned the trust of homeowners, installers, and experts. The sheer volume of reviews on platforms like TrustPilot showcases the reliability and aftercare of Worcester Bosch, with almost 40,000 customers sharing their experiences. The brand’s average rating of 4.6 out of 5 stars speaks volumes about their commitment to quality.

Which? Boiler Survey Results further underline Worcester Bosch’s unwavering reliability. The brand has maintained the Which? Best Buy Award for over a decade, and their UK presence ensures that parts are readily available, making customer service a breeze..

The Greenstar 4000 Combi Boiler is available in two power outputs: 25kW and 30kW. The 25kW model provides a heat output of 25kW and a flow rate of up to 10.2 liters per minute, making it suitable for smaller properties or flats with lower hot water demands. On the other hand, the 30kW model offers an additional 5kW of power and a flow rate of up to 12.3 liters per minute, making it an excellent choice for medium-sized properties with higher hot water requirements.

25kw – hot water flow rate at a rise of 40 °C – 9.1 L/min
25kw – hot water flow rate at a rise of 35 °C – 10.2 L/min

30kw – hot water flow rate at a rise of 40 °C – 10.8 L/min
30kw – hot water flow rate at a rise of 35 °C – 12.3 L/min

Central heating maximum output for the 25kw and the 30kw is 25kw

To Achieve maximum hot water flow rate a minimum static mains water pressure of 1 bar for the 25kw is required and 1.2 bar is needed for the 30kw model.

Efficiency: A-rated (94%)

When it comes to efficiency, the Worcester Bosch Greenstar 4000 is accredited with an impressive A rating, boasting an efficiency of 94%. This high energy efficiency rating makes it an eco-friendly choice for homeowners looking to reduce their carbon footprint and save on energy bills.

Modulates as low as 3kw – The 4000 is capable of modulating down to 3kw which keeps the gas bill down as it uses less gas.

Seasonal space heating energy efficiency – 94% 
Energy efficiency class – A
Water heating energy efficiency – 85%
Water heating energy efficiency – A


The Quiet Mark:

The Quiet Mark is an international certification program recognised for its stringent noise reduction standards, awarded to products and technology that meet specific criteria. Founded by the Noise Abatement Society in the UK, the Quiet Mark aims to promote quieter technology and raise awareness about reducing noise pollution. Products that receive the Quiet Mark certification have undergone rigorous testing by acoustic experts to ensure they meet noise reduction standards. The certification logo indicates to consumers that a product has been independently verified as meeting these standards, making it easier for consumers to choose quieter and more peaceful products, such as the Worcester Bosch Greenstar 4000 boiler

Worcester Bosch Greenstar 4000 quiet and reliable

Warranty: 5/5 Stars

Warranty plays a significant role in boiler selection. The Worcester Bosch Greenstar 4000 offers an industry-leading 10-year guarantee for parts and labour when purchased through Expert Heat. This extensive coverage provides homeowners with peace of mind and security for the next decade, ensuring a worry-free heating solution.

Price Point: 4/5 Stars

The Worcester Bosch Greenstar 4000 is considered a mid-range boiler, offered by a premium brand. While it’s not the cheapest boiler available, it certainly represents excellent value for money, especially when considering the quality and aftercare that Worcester Bosch is known for.


The Worcester Bosch Greenstar 4000 is a mid-range boiler that combines essential features with a sleek exterior, all at a competitive price. Replacing the highly regarded Greenstar i range, the 4000 retains all the strengths of its predecessor while introducing improvements such as quieter operation and higher hot water output. The improved flow rate ensures faster hot water delivery to taps and showers. Worcester Bosch’s commitment to innovation is evident with features like the intelligent filling system, frost protection, ECO mode, and wireless connectivity. The aesthetically pleasing exterior design adds a modern touch to your heating setup, making it not only a great performer but also a stylish addition to your home.

With Worcester Bosch’s impressive track record of winning the Which? Best Buy Award for over a decade, coupled with their exceptional TrustPilot reviews and an industry-leading 10-year guarantee, the Greenstar 4000 stands as a reliable choice. If you’re seeking a dependable boiler from a brand with a history of excellence, the Worcester Bosch Greenstar 4000 is certainly worth considering.

Looking for the best deal on a Worcester Bosch Greenstar 4000?

If you’re interested in getting your new boiler installed quickly and efficiently, consider Expert Heat. We offer Gas Safe installation within 24 hours, receive high Trustpilot ratings, and provide a price match guarantee, ensuring you get the best value for your investment. With multiple payment options, and a fixed price guarantee, Expert Heat is the perfect partner for your boiler installation journey.

Worcester Bosch 4000 combination boiler


New boiler quote in less than 1 minute

New Boiler quote in less than 1 minute


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