Worcester Greenstar Si Compact Combi

The Worcester Bosch Greenstar Si Compact Gas Boiler is a newer model in the Worcester Bosch range. In this review, the team at Boilerhut, comprising engineers with over 40 years of experience, have taken a look at this boiler and have detailed their thoughts.

Price (Installed): From £2160 (inc. VAT)

Worcester Bosch Greenstar Si Compact Gas Boiler Technical Specification

ManufacturerWorcester Bosch
ModelGreenstar Si Compact
Efficiency Rating94%
Energy Efficiency ClassA Rated
LPG CompatibleYes
Warranty5 years*
Central Heating Max. Output24 kW
MountingWall Mounted
Weight32.9 kg
Dimensions690mm (Height) x 390 (Width) x 280mm (Depth)

* this can be upgraded to 10 years when installed by a Worcester Bosch Accredited Installer.

The Worcester Bosch Greenstar Si Compact Gas is available in the following sizes: 25 and 30 kW

kW SizeFlow Rate
25kW8.9 l/min
30kW10.7 l/min

Worcester Bosch Greenstar Si Compact Key Features

  • Holds an ‘A’ energy efficiency rating, with efficiency up to 94%
  • Extremely compact and lightweight design, making it easy to install
  • Can be installed in a cupboard because of its small size, or wall-mounted
  • Simple to use manual control panel.
  • Includes frost protection to reduce risk if installed in a non-insulated part of your home
  • Provides a heating output of 24 kW and hot water output of 30 kW

About the Worcester Bosch Greenstar Si Compact Gas Boiler

  • The Worcester Bosch Greenstar Si Compact Gas is extremely compact given its output, making it a popular choice for small homes and apartments
  • Easy to install in a standard cupboard in a kitchen, bathroom or airing cupboard
  • Compatible with smart thermostats
  • Part of the Greenstar ranger which has won Which? ‘Best Buy’ award for several consecutive years

Our thoughts on the Worcester Bosch Greenstar Si Compact Gas Boiler

The Worcester Bosch Greenstar Si Compact Gas Boiler is a reliable and energy-efficient boiler that will provide continuous hot water and simultaneously run heating efficiently in a home with one bathroom. However, if you have a bath, you will most likely need the 30i model.

One of the benefits of this compact model is that it does not need to be installed alongside a tank or cylinder which further reduces the space required for your heating system.

Which? Best Buy award

Worcester Bosch has won the highly regarded Which? Best Buy award for its boilers for several years. Over the years, they have developed a reputation as a reliable and quality manufacturer for boilers both in the UK. However, this quality has been surpassed by other boiler manufacturers in recent years

Energy efficiency

Worcester Greenstar Si Compact Gas includes two models – 25 kW and 30 kW. The 25 kW model is appropriate for smaller homes with one bathroom. 

Both boiler models are rated highly for energy efficiency. This is even more pronounced when used in conjunction with the latest smart thermostat technology. This is a high-performance boiler that has been designed with low energy usage in mind. However, this efficiency won’t last forever, as we go on to below.

Aluminium heat exchanger

A downside of the Worcester Bosch Greenstar Si Compact Gas Boiler though and the Worcester Bosch range, in general, 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 warranty the repair costs for this will be costly.

Hot water when you need it

The Si models will provide a minimum of 8.9 litres per minute flow rate of hot water meaning you will never have to wait for the boiler to heat up before taking a shower. This instantaneous heating not only reduces energy waste but also helps to reduce water inefficiency.

Assembled in the UK

The Worcester Bosch Greenstar Si Compact is assembled in the UK at Worcester Bosch’s factory and head office in Worcestershire. However, it is only assembled here with many of the individual components in the boiler being manufactured elsewhere by third parties.

Plastic components 

On the subject of parts and components, it should be noted that many of them used in the Worcester Bosch Greenstar Si Compact are made of plastic as opposed to the higher quality brass components utilised in equivalent boilers from rival manufacturers. 

Wide availability of parts 

That said, the parts and components are widely available across the UK. You can find these at Screwfix, Plumbase and other plumbing merchants both in-store and online.

Get a FREE Boiler Quote