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Worcester Bosch Greenstar 25i Combi Boiler - Review


Worcester Bosch has become a household name for their continuous manufacturing of up-to-date boilers. Worcester was founded in 1962, later named Worcester Bosch in 1992 due to an acquisition by the Robert Bosch GmbH. Worcester Bosch has transformed over the last five decades from a small engineering company to the UK’s favourite boiler manufacturer.

We took a good look at Worcester Bosch's 25i combi boiler, just how good is the UK's most popular boiler?

Will the Worcester Bosch Greenstar 25i be suitable for my home?

The Worcester Bosch Greenstar 25i combi boiler is currently their best-selling combi boiler and is suited to smaller flats and houses (1 to 3 bedrooms and 1 bathroom). With a high ErP (Energy Related Product) rating of 93% and a lightweight design, the 25i is the perfect successor to the 24i Junior. With a central heating output of 24kW, a domestic hot water output of 25kW and a flow rate of 10.2 litres/minute, the Greenstar 25i offers an efficient heating and hot water experience.

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There are a wide variety of controls to choose from, which range from mechanical to smart options. The control panel on the boiler itself is what you’d normally expect to find once you’ve opened the flap on the Greenstar 25i. In addition to its control panel, you have the option of using a Smart Thermostat to have all of the control of managing your heating and hot water from a smartphone app.

This is a great option for you if you’re looking to have closer control of your energy use while setting heating schedules using the app on your mobile phone or other smart devices. However, if you’re looking to stick with digital thermostats, the Greenstar Comfort thermostat is a good choice.

Worcester Bosch has massively improved the simplicity with which engineers can access main components and parts within the boiler. An engineer can easily diagnose issues due to the control panel on the boiler, so that if a problem should arise, an engineer can perform diagnostics over the phone and easily fix it in person if needed, reducing call-out fees.

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Worcester Bosch offers a standard 5-year warranty free of charge for all their Greenstar boilers, however, if you have this boiler installed by Hometree, you can extend your warranty by a further 5 years.

Energy Efficiency

The Worcester Bosch Greenstar 25i lives up to its name as a “green” boiler. With an ErP (Energy-related Product) rating of 93% (which is an A-grade), you’re not just looking at a high-performance boiler but you'll also save money on those monthly energy bills while reducing your household's carbon footprint.

The ErP directive tests each product to see if it passes certain criteria based on their energy efficiency. For example, how the design of the boiler has been improved to lower carbon footprint and decrease the amount of wasted energy.


In conclusion, the Worcester Bosch Greenstar 25i combi boiler is the perfect choice for a smaller home with one bathroom and up to 3 bedrooms. It packs a punch while being one of the highest efficiency rated boilers on the market.

The Greenstar gas boiler series has won the coveted Which? Best Buy award for 7 years running, which is a testament to the quality of the company’s products. It’s certainly an improvement over the 24i Junior and boasts a list of benefits from high efficiency to improved controls.

If you're looking for a more space-saving solution, check out our review of the Worcester Bosch Greenstar 25Si Compact.

 Worcester Bosch Greenstar 25i
ErP rating (energy efficiency)A (93%)
Size (HxWxD in mm)710x400x330
Heating output (kW)24
How water output (kW)25
Flow rate (litres/min)10.2
Standard warranty (years)5 (extended warranties available)
Other available sizes (kW)30

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Which? boiler review

The consumer group Which? review each boiler on the market to find the most (and least) reliable boilers according to a survey completed by thousands of boiler owners. In each review, Which? supply a brand score percentage and star ratings for each category. Take a look at the Worcester Bosch Greenstar 25i ratings below:

Which? Score 
Efficiency rating★★★★★
Brand reliability★★★★★
Brand customer score★★★★★
Ease of repair★★☆☆☆
Ease of service★★★☆☆
Availability of parts and spares★★★★★
Build quality★★★★★
Engineer recommendation★★★★★
Brand score86%

If you'd like to learn more about the Worcester Bosch Greenstar 25i combination boiler, check out our quick video review below:

Video transcript

Hello and welcome to Hometree, home of the stress-free boiler installation. Today we are looking at the Worcester Bosch Greenstar 25i combi gas boiler one of our best-selling combination boilers here at Hometree. If you didn't already know, Worcester Bosch is a UK-based manufacturer with 50 years of experience in manufacturing energy products and is a much-loved boiler brand due to reliability. For 8 years running, they have been a top trusted brand in the Which? annual boiler survey.

In our review, we are going to run you through all of the elements of the Worcester Bosch Greenstar 25i combi boiler and why this might be the right boiler for you.

The Greenstar 25i is a smaller version of the popular Worcester 30i. This powerful little combi boiler can supply up to 10. 2 litres of hot water per minute. It's important that there is enough mains water pressure flowing into this boiler, but don't worry our Hometree engineers can advise you on this. The hot water output of the 25i is 25 kilowatts which is great for smaller homes with two to three bedrooms and one bathroom.

The 25i comes in an average-size which can fit in most kitchen or hall cupboards. This excludes any space needed for ventilation, pipework or cables. The Greenstar 25i comes with a standard control panel on the boiler which allows you to switch the boiler on and off or lower the output. It's worth noting that each Hometree boiler installation comes with a free smart thermostat so you'll be able to control your heating from your smartphone. Smart thermostats are compatible with this model.

For extra peace of mind, the simple build of the Greenstar 25i means it is easier to diagnose problems or replace parts in the boiler. With this Worcester Bosch model, there is a five-year standard warranty. But if you choose Hometree, we'll provide a 10-year warranty for free for your peace of mind. The 25i has an energy efficiency rating of 93% which is also an A-grade. We all want to avoid wasting energy and spending extra money, which is why this boiler is an excellent choice.

The Worcester Bosch brand has an outstanding 86% Which? score as well as a 5-star customer score. It's not surprising really when you look at the exceptional efficiency, the brand’s reliability, availability of parts and spares and that is easy to maintain.

The team at Hometree can discover which boiler type and size is suitable for you, just by asking some simple questions on our website or over the phone. Hometree will then provide you with an A-rated boiler and boiler installation at a great price, and at a time that suits you. Unlike some traditional boiler installers, we won't send pushy salespeople to your home instead we will do a video survey using a smartphone with one of our Gas Safe engineers.

At Hometree, we know that a warm home is too important for a broken boiler to get in the way so we provide stress-free border installations. To get the right boiler, at a great price, fitted by a local Gas Safe engineer at a time that suits you, visit