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Worcester Bosch Greenstar 24i Junior Combi Gas Boiler


The Worcester Bosch Greenstar 24i Junior Combi Boiler is part of a product range released several years ago. Compared to more “recent” boilers, it doesn’t promise much. A lot of it has to do with its overall output rating. Ideally, a 24kW combi boiler suits small to medium-sized households with low to medium demand for hot water and central heating.

Unfortunately, Worcester Bosch has discontinued its manufacture. Nonetheless, there are still some units available in the market. The Worcester Bosch 24kW Combi Boiler replaced this unit.

If it suits you, you’ll be happy to know that this boiler comes with some features that might be worth your attention.

Continue reading for more on the Worcester Bosch Greenstar 24i Junior Combi Boiler.

Worcester Bosch Greenstar 24i Junior Key Features

  • It’s a condensing boiler.
  • It has an overall efficiency rating of 90% (SEDBUK Band A-rated).
  • Aluminium and silicon cast heat exchanger
  • ERP A-rated for both central heating and hot water production
  • It has a central heating and hot water max output of 24kWs
  • Compatible with Greenskies solar panels (To help save on heating costs).
  • It can serve up to 10 radiators.
  • It has a hot water flow rate of 9.8 litres per minute.
  • Compatible with external temperature control systems like room thermostats and radiator valves.
  • It comes with a standard 10-year labour and part warranty.
  • It offers extensive flue options.
  • It comes with a wall plate and pre-plumbing jig.
  • It’s compatible with twin-horizontal and vertical flue systems.
  • Relatively compact dimensions of 700mm Height by 400mm Width by 330mm Depth.
  • It weighs 27.1kgs.


The Greenstar 24i Junior Combi Boiler’s design is simple but praiseworthy. Generally, everything component looks and feels well fit. Although it only comes in white, we appreciate its tidy finish. On top of that, its controls and buttons are well-hidden behind a facia board to give it an overall neat appearance.

Unfortunately, it doesn’t come with an LCD. Its interface consists of a rest control button, an ECO mode, temperature knob, pressure gauge, and space for a timer (Optional).

As far as compactness is concerned, the Greenstar 24i Junior Combi Boiler is small enough to fit inside a standard kitchen cabinet. You’ll have to worry about the odd-looking boiler cramping your home’s decor.

Fuel and efficiency

Although natural gas is advertised as the unit’s main fuel, there are variants in the same product range that can operate on LPG.

Considering its age, an efficiency rating of 90% is quite impressive. On top of that, it’s also ErP A-rated for both central heating and domestic hot water production. In a proper setup, the Greenstar 24i Junior Combi Boiler will help you save money on heating costs.

If that wasn’t enough, this boiler is also categorized in the NOx Class 5—Thanks to its low NOx and CO emission, it will reduce your household’s carbon footprint.

Summing all these factors together, it’s easy to understand why the Energy Saving Trust decided to endorse the Worcester Bosch Greenstar 24i Junior Combi Boiler.

Power output rating

Indeed, an output rating of 24kW isn’t the most impressive in the market. Nonetheless, it will easily cater to small and medium-sized households with two bedrooms and one bathroom. Additionally, its decent hot water flow rate of 9.8 litres per minute allows it to operate no more than 10 radiators.

If you’re interested in a more powerful unit, then you should check out the Greenstar 28i Junior Combi Boiler. An output rating of 28kW is an upgrade that allows you to add two more radiators and a bathroom to the equation.

Installation and servicing

Weighing at 27.1kgs, the Greenstar 24i Junior Combi Boiler is among the lightest in the market. Therefore, it won’t require more than two engineers to install. Additionally, it’s also compatible with a wide range of flue options (Both horizontal and vertical systems).

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