Worcester Bosch Greenstar 25Si Compact

What is the Greenstar 25Si Compact?

The Greenstar 25Si Compact is a wall-mounted gas combi boiler and the entry-level model in the Greenstar Si Compact range. Designed for smaller properties and apartments, it was built to fit inside a standard kitchen cupboard while delivering reliable heating and hot water from a compact footprint.

The 25Si Compact featured Worcester Bosch’s WB7 heat exchanger, providing a flow rate of 10.2 litres per minute, making it well suited to homes with a single bathroom and moderate hot water demand. It provided instant hot water on demand from the mains without the need for a cylinder or storage tank.

For homes needing slightly more hot water performance, the 30Si Compact offered the same compact dimensions with a higher flow rate. The 25Si Compact was part of the Greenstar Si Compact range, a popular and dependable series for smaller properties across the UK.

> Explore the full Worcester Bosch Greenstar range

Greenstar 25Si Compact: Key Specifications

✔ Boiler type: Combi boiler

✔ Central heating output: 24kW

✔ Hot water output: 25kW

✔ Efficiency rating: A rated / 94%

✔ Fuel type: Natural gas or LPG

✔ Dimensions: 690mm x 390mm x 280mm

✔ Flow rate: 10.2 litres per minute

✔ Frost protection: Yes

✔ Smart control compatible: Yes, including Bosch EasyControl

✔ Suitable for: 1 to 2 bed homes, up to 10 radiators, 1 bathroom

Who is this boiler suitable for?

The 25Si Compact was designed for the smallest domestic properties where space was limited and hot water demand was modest. It is best suited to properties with:

• 1 to 2 bedrooms
• 1 bathroom
• Up to 10 radiators
• No existing hot water cylinder
• Limited installation space, such as a kitchen cupboard

The 25Si Compact is ideal for running a shower but will be slow to fill a bath due to its flow rate of 10.2 litres per minute. For homes with a bath and shower, the 30Si Compact with its higher flow rate of 12.3 litres per minute was the better choice within the same range. If you already have a 25Si Compact installed and are unsure whether to service, repair or replace it, our engineers can assess your system and give you honest advice.

Servicing and repairing your Greenstar 25Si Compact

Although the 25Si Compact is no longer manufactured, it can still be serviced and repaired. Parts remain widely available for this model and our Gas Safe engineers carry out full services and fault diagnosis across Buckinghamshire, Berkshire, West London and surrounding counties.

Regular servicing is important for any boiler, but particularly for older models. An annual service helps to:

• Maintain efficiency and keep running costs down
• Identify worn components before they cause a breakdown
• Keep your boiler operating safely
• Satisfy any remaining warranty or insurance requirements

> Book a boiler service

If your 25Si Compact has developed a fault, our engineers carry a wide range of Worcester Bosch parts and aim to resolve most repairs in a single visit.

> Book a boiler repair

When to consider replacing your 25Si Compact

If your boiler is over 12 to 15 years old or experiencing repeated breakdowns, replacement is often the more cost-effective long-term decision. The 25Si Compact has been replaced by the Worcester Bosch Greenstar 4000, which offers meaningful improvements across warranty and controls while maintaining a compact footprint suitable for smaller homes.

The Greenstar 4000 25kW is the natural modern equivalent for homes currently running a 25Si Compact. It delivers a longer warranty and full compatibility with the Bosch EasyControl smart thermostat.

Greenstar 25Si Compact vs Greenstar 4000 25kW

Efficiency: 94% vs up to 94%

Warranty: 2 to 5 years vs up to 10 years

Controls: Basic display vs smart control ready

ErP rating: A rated vs A rated

Status: Discontinued vs current model

> Learn more about the Greenstar 4000

> View boiler costs

> Explore finance options

Why choose Heppelthwaite – Red Van Plumbers?

Fewer than 5% of UK installers achieve Worcester Bosch Platinum Accredited status. As Platinum Accredited Installers, we install, service and repair the full Greenstar range, including legacy Si Compact models, across Buckinghamshire, Berkshire, West London and surrounding counties.

• Platinum Accredited Worcester Bosch Installers
• Family-run business established 1948
• Gas Safe registered engineers
• Free fixed quotations with no hidden costs
• Up to 10-year warranty available on new Greenstar 4000 installations

> Request a free quote or call 01628 533 550

FAQs – Worcester Bosch Greenstar 25Si Compact

Is the Worcester Bosch Greenstar 25Si Compact still available to buy?

No. The 25Si Compact is no longer manufactured. The modern equivalent is the Worcester Bosch Greenstar 4000 25kW combi boiler, which offers an improved warranty and smart control compatibility while maintaining a compact design suitable for smaller homes.

Can the Greenstar 25Si Compact still be serviced?

Yes. Parts remain widely available and our Gas Safe engineers service and repair all Si Compact models across Buckinghamshire, Berkshire and West London. Annual servicing is recommended to maintain efficiency and safety.

What replaced the Greenstar 25Si Compact?

The Greenstar 25Si Compact was replaced by the Worcester Bosch Greenstar 4000. The 4000 offers smart control compatibility and up to a 10-year warranty when installed by a Platinum Accredited Installer.

What is the difference between the 25Si Compact and the 30Si Compact?

Both models share the same compact dimensions and central heating output of 24kW. The key difference is the hot water output and flow rate. The 25Si Compact delivers 10.2 litres per minute, while the 30Si Compact delivers 12.3 litres per minute. If your home has a bath and shower, the 30Si Compact was the more appropriate choice.

Will the Greenstar 25Si Compact fit in a kitchen cupboard?

Yes. The 25Si Compact was specifically designed to fit inside a standard kitchen cupboard at 690mm x 390mm x 280mm. This compact footprint made it an ideal choice for flats, apartments and smaller homes with limited installation space.

How long should a Greenstar 25Si Compact last?

With regular annual servicing, a well-maintained 25Si Compact can last between 12 and 15 years. If your boiler is approaching or has exceeded this age, it may be worth considering a boiler replacement to avoid repeated repair costs.