Worcester Bosch Greenstar 25i Boiler Review

Company type: Manufacturer

HQ: Worcester, England

Founded: 1962

CEO: Carl Arntzen

The Worcester Bosch Greenstar 25i is a compact combi gas boiler that comes with a bunch of useful features. Along with its more powerful sibling, the 30i, it is a part of the widely popular Greenstar i range. In this review, we will tell you more about its advantages, energy efficiency rating and other useful specifications.

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Is the Worcester Bosch Greenstar 25i a good choice for you?


The Worcester Bosch Greenstar 25i is an entry-level model of the Greenstar i range, famous for its compact and light design. This makes the Worcester Greenstar 25i easy to install in kitchen cupboards, utility rooms and airing cabinets. If you are looking for a relatively small boiler that will save you some space, Greenstar 25i is a good option.

The Worcester Bosch Greenstar 25i has a maximum hot water output of 25kW, meaning it can supply up to 10 radiators with hot water. Most properties suitable for this kW output are likely to have no more than 1 shower and only a couple of bedrooms. This includes small apartments, flats and 2-bedroom terraced houses.

Below is a rough guide to what hot water output is recommended for different sized homes:

Property type No. of radiators No. of bathrooms Recommended hot water output
Flat or Small house Up to 10 1 24-27 kW

Greenstar 25i

Medium house Up to 15 1 or 2 28-34 kW
Large house 15-25 2+ 35-42 kW

When choosing a boiler, also take into consideration the boiler's hot water flow rate, as this will determine the water pressure in your showers. The Worcester Bosch Greenstar 25i has a flow rate of 9 l/m, which means 9 litres of water per minute will pass through your taps or shower. For smaller properties, a flow rate of 9 litres per minute or more is acceptable, so the Greenstar 25i's flow rate is adequate for homes with one bathroom.

If you live in a house with 2 or more showers or more than 3 bedrooms, it’s likely you are going to need something more powerful. In this case, we recommend taking a look at our Worcester Bosch Greenstar 30i boiler review as this is a step up from the 25i. You might also consider the new 4000 range that comes with additional features at a similar price.

Is the Worcester Bosch Greenstar 25i energy efficient?

Worcester Bosch Greenstar 25i is 93% energy efficient, which gives it an ‘A’ efficiency rating. After the recent changes in boiler regulations, ‘A’ is now the highest possible rating a boiler can achieve when it comes to boiler efficiency.

However, it is important to note that there are models on the market that outperform the Greenstar 25i, for example, the Worcester Bosch Greenstar 8000 Style 30kW with its 95% efficiency. Although it may not sound like such a big difference, securing a higher energy efficiency percentage means paying less for your total energy bills.

Key features

An easy-to-use boiler control panel

The Worcester Bosch Greenstar 25i comes with a simple four-button control panel that lets you adjust the temperature of your central heating and hot water. The Heatronic control panel also has an upgraded interface with text descriptions and error codes; when there is a problem with the boiler, the display will flash the corresponding fault code, making it much easier for an engineer to diagnose and rectify the problem.

Compatible with a range of boiler controls and thermostats

When you have the boiler installed, you’ve got the option to have a standard thermostat or a 'smart' one. The latter lets you adjust heating schedules using the app on your smartphone wherever you are and control the heating system remotely. One of the newest controls that can be used in conjunction with the 25i is the Worcester Bosch Wave. It can increase the efficiency of your Worcester Bosch Greenstar 25i by up to 4% by adapting to the homeowner's behaviour and automatically adjusting the temperature.

Worcester Bosch Greenstar 25i is still perfectly compatible with RF (radio frequency) thermostats and the majority of wired thermostats out there. Although Worcester Bosch controls are highly reliable, if you ever experience issues with your wireless thermostat, follow this link for some useful advice.

No need to dismount the boiler during maintenance

The Worcester Bosch Greenstar 25i’s components are completely serviceable from the front, which means you won't have to remove the boiler from the wall to get to the expansion vessel and other key boiler components. This will make your engineer’s life easier when he comes in to fix faults and replace parts.

Comes with protection against pipe freezing

Frozen condensate pipes are one of the most common heating system problems our customers face during the winter months. The pipe that removes acidic water from the heating system is relatively thin and, in most houses, flows into a drain outside. When the pipe freezes, the condensate will back up into the boiler, potentially causing the entire system to fail.

Fortunately, the Worcester Bosch Greenstar 25i has a large condensate siphon that helps to minimise this problem. The installed condensate discharge pipe can withstand temperatures as low as -15°C. This feature will save you money and time in the long run, as the pipe is unlikely to require additional insulation or costly service visits.

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Worcester Bosch Greenstar 25i Technical Specifications

Width 400 mm
Height 710 mm
Depth 330 mm
Weight 31.7 kg
Fuel type Gas
Display type Digital
Energy Efficiency Class A
Flow rate 9 L/min
Max kW output 25 kW
Sound power 50 dB
Standard Warranty 5 years

Alternatives to Worcester Bosch Greenstar 25i

In 2020, The Greenstar i range, which includes Worcester Bosch Greenstar 25i, was discontinued and replaced by the updated Greenstar range. If you are looking for a 25i replacement, the Greenstar 2000 combi boiler might be a great choice for you. The new model comes in a new sleek design with incredibly quiet operation, while keeping the benefits of compact size and easy-to-use controls. Click below to explore the Greenstar 2000 and other combi boilers offered by Worcester Bosch.

Discover Worcester Bosch Combi Boilers

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