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Witten by Bernard Morgan (Engineer).
First Published: May 20, 2021. Updated: November 21, 2023

Worcester Bosch Greenstar 4000 Gas Boiler Review

New for 2021, the Worcester Bosch Greenstar 4000 gas boiler is the successor to the hugely popular Greenstar i. Taking all of the best bits from the Greenstar i, the Greenstar 4000 is available in both natural gas and LPG.

The Worcester Bosch Greenstar 4000 range comprises 25kW and 30kW combi boilers, and as a system boiler in 12kW, 15kW, 18kW, 21kW and 24kW outputs.

In this review, we will cover the main features of the Worcester Bosch Greenstar 400 gas boiler, so you can establish if it’s right for your home.

Technical Specification:

Manufacturer Worcester Bosch
Model Greenstar 4000
Condensing Yes
Efficiency Rating 94%
Energy Efficiency Class A Rated
LPG Compatible Yes
Warranty Up to a 10-year guarantee
Central Heating Max. Output 30 kW
Mounting Wall Mounted
Weight TBA
Dimensions 710mm (Height) x 400 (Width) x 310mm (Depth)

Key Features:

  • Available as a combi boiler and a system boiler
  • Available in natural gas and LPG
  • An upgraded version of the Greenstar i
  • Features front access to all key components for ease of installation and future servicing and maintenance
  • Offers hot water flow rates of up to 12.3 l/min
  • Can be integrated with Bosch EasyControl which allows you to control your home’s heating wherever you are via a mobile phone or tablet
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  • Designed to be a replacement boiler for customers who currently have a Greenstar
  • Junior Si boiler (2005-2015), with minimal pipework changes needed
  • Designed to be compact and lightweight so that it can be fitted inside a standard kitchen cupboard
  • Has a small size and low weight
  • Quieter operation than the Greenstar i
  • Increased hot water flow rates compared to the Greenstar i
  • Assembled in Worcester, UK
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Our thoughts:

New for May 2021, the Worcester Bosch Greenstar 4000 is based upon Worcester Bosch’s best selling Greenstar i range. Taking the best bits of this boiler range and improving them, the Worcester Bosch Greenstar 4000 range features an exterior design that follows the modern aesthetics of the Worcester Bosch 8000 Style range.

Worcester Bosch is touting this boiler range as a direct replacement for customers who currently have Greenstar i, i Junior and Si boilers available from 2005-2015. With these boilers reaching the end of their service life, Worcester Bosch has designed the Greenstar 4000 range to be able to fit the same footprint as these boilers with a simple switch wall-frame and minimal pipework changes required.

With improvements to the features offered by the Greenstar i range, the Greenstar 4000 range operates at a quieter volume than the previous range. Improvements also come to the flow rates offered by the combi boiler versions of this range, with the 25kW model offering 10.2l/min and the 30kW offering 12.3l/min.

Compatible with a wide range of controls 

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

  • Worcester Bosch MT20 mechanical timer
  • Worcester Bosch Greenstar Comfort+ thermostat
  • Worcester Bosch Comfort+ Stat RF thermostat
  • Worcester Bosch Comfort+ II RF thermostat
  • Worcester Bosch Easy Control smart thermostat

A quality boiler from a trusted brand

Worcester Bosch has won the coveted Which? Best Buy award for its boilers for over ten years. But what makes Worcester Bosch so special? The engineering and precision that goes into creating Worcester Bosch boilers is great. They also have an excellent rating on Trustpilot, reflecting their commitment to customer service and quality products.


The Greenstar 4000 range comes with a guarantee of up to 10 years. However, this is only when the boiler is installed by a Worcester Accredited Installer. Otherwise, it only has a 2-year guarantee.

Aluminium heat exchanger

A downside of the Worcester Bosch Greenstar 4000 boiler range though, is its usage of an aluminium heat exchanger. An aluminium heat exchanger will offer great efficiency when the boiler is first installed. However, after a few years aluminium will start to corrode and corrosion equals a drop in efficiency. So whilst this boiler offers up to 94% efficiency from installation, this won’t last forever.

It should be noted that the heat exchanger is covered by the guarantee but once out of guarantee the repair costs for this will be costly.

Wide availability of parts
As the Worcester Bosch Greenstar 4000 boiler range is assembled in the UK, parts are widely available. If you need a replacement item you can find spare parts at Screwfix, Plumbase and other plumbing merchants both in-store and online

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