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Worcester Bosch Greenstar Heatslave II Boiler

The Worcester Bosch Greenstar Heatslave II is designed for homes of all sizes and has been hailed the UK’s favourite oil combi boiler.

Bragging a sleek, modern design, the Greenstar Heatslave II by Worcester Bosch is an energy efficient combi boiler that is perfect for small, medium and large homes. It’s a floor-standing boiler that will fit under most kitchen worktops and can be used with an impressive selection of optional controls to improve efficiency and comfort levels. Furthermore, this model has been labelled as a Which? Best Buy and one of the UK’s most popular oil combination boilers.

How Much Does this Boiler Cost?

As the Worcester Bosch Greenstar Heatslave II comes in three central heating outputs of 18kW, 25kW and 32kW, prices vary according to these outputs. We can, however, tell you that prices range between around £2,200 and £2,500 including VAT. You’ll need to find out which size (kW output) is correct for your home before knowing how much the boiler is going to cost you. They’ll be fitting fees on top of the boiler cost as well, so be sure to contact different suppliers and companies to find the most competitive quote on both the boiler and installation.

How will I know if this Boiler is Suitable for My Home?

This is a combi boiler (or combination boiler), meaning you won’t need separate loft tanks or a hot water cylinder in order for the boiler to provide efficient heating and hot water. Combi boilers are usually recommended for smaller homes because they don’t require any additional components (such as tanks or cylinders). One of the great things about combi boilers is that they heat water directly and almost instantly from the mains so that they can supply hot water on demand, ensuring energy is only used when you need hot water.

The larger your property and the more rooms you have, the higher the boiler central heating output will need to be. Because the Worcester Bosch Greenstar Heatslave II is available in a range of kW outputs to suit most properties, you’ll need to seek advice from on OFTEC registered engineer who will be able to recommend the correct output for your home.

Is it a High Efficiency Boiler?

Yes. The Worcester Bosch Greenstar Heatslave II is an A-rated oil combi boiler with an excellent efficiency of over 90%. It’s also compatible with a selection of optional controls, such as the Greenstar Comfort I and the Greenstar Comfort II programmable room thermostat for greater efficiency. Whether you chose to use the boiler as it comes or with an optional control, it can help to not only lower your fuel bills but also your carbon footprint.

Does this Boiler have a Good Range of Controls and Features?

This boiler does indeed have some great controls and features. The user controls are actually hidden behind a panel and include a reset switch, system pressure gauge and a separate central heating and hot water temperature control. It even has an ‘Eco Hot Water Mode’ to ensure you save as much energy as possible. The boiler also has front access to components and a one-piece baffle for ease of servicing. In addition to being compatible with a range of optional Greenstar controls, the Worcester Bosch Greenstar Heatslave II works with water that has been heated by green sources to increase efficiency and reduce your bills even further. Plus, you can use the boiler with the Bosch EasyControl that allows you to monitor your energy use and tailor your hot water demand and heating in individual rooms from a smartphone or tablet.

How long is the Warranty on this Boiler?

You’ll receive a 2-year parts and labour warranty as standard when you purchase the Greenstar Heatslave II. We recommend you always check the Worcester Bosch website before purchasing this boiler because the brand sometimes offers a longer promotional warranty on its oil boilers.

Summary of Important Information

  • Priced between £2,200 and £2,500
  • Heating output of 18kW, 25kW or 32kW
  • Hot water flow rates of 15, 18 or 22 litres per minute
  • Dimensions of 855mm (H) x 520mm (W) x 600 (D)
  • Uses oil as its fuel source
  • A-rated for efficiency
  • Smart compatible
  • Solar thermal compatible
  • 2-year warranty as standard

Greenstar Heatslave II By Size and Price

ModelTypeDimensionsMaximum Flow RateOutputEfficiency RatingTypical Price
Greenstar Heatslave II 18CombiH – 855 mm
W – 520 mm
D – 600 mm
22 l/min18 kWA 90% and above£2200
Greenstar Heatslave II 25CombiH – 855 mm
W – 520 mm
D – 600 mm
22 l/min25 kWA 90% and above£2400
Greenstar Heatslave II 32CombiH – 850 mm
W – 520 mm
D – 600 mm
22 l/min32 kWA 90% and above£2500

Pros and Cons


It’s not difficult to see why homeowners and heating engineers have so many positive things to say about the Worcester Bosch Greenstar Heatslave II. Below, you can find all of the pros and cons of this fantastic oil-fired combi.

  • Awarded Which? Best Buy with a score of 87%
  • Fits underneath a standard kitchen worktop
  • Suited to small, medium and large homes without a mains gas supply
  • No need for separate cylinder or loft tanks
  • Simple boiler controls and clear temperature display
  • Eco hot water mode – saves energy
  • Provides maximum energy efficiency – reduce fuel bills and carbon emissions
  • Compatible with solar thermal – additional savings
  • Compatible with Bosch EasyControl – can tailor hot water times and heating temperatures from your smartphone or tablet, even when you’re not at home
  • 5-year guarantee on the primary heat exchanger


  • 2-year warranty – would prefer a longer standard guarantee