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Last updated: 22nd January, 2024


Worcester Bosch Greenstar CDi Highflow: Floor-Standing Combi Review

Worcester Bosch Greenstar CDi Highflow: Floor-Standing Combi Review

Key takeaways

  • The Greenstar CDi Highflow caters to the high water demands of large homes.
  • Efficiency ratings are high, promoting energy savings.
  • It combines heating and hot water generation, benefiting space-limited properties.

The Worcester Bosch Greenstar Highflow CDi series stands out with its floor-standing design and high hot water flow rates, catering specifically to larger homes with more than one bathroom.

In the landscape of domestic heating and hot water solutions, one prominent offering stands out for larger homes with greater demands: the Worcester Bosch Greenstar CDi Highflow. Renowned for its robust performance and capacity to provide continuous hot water, this floor-standing combi boiler has established itself as a powerful presence in the industry. 

The Greenstar CDi Highflow series is specifically engineered to meet the needs of properties with multiple bathrooms where the simultaneous use of showers and taps is common.

The design features a floor-standing configuration known for its industry-leading flow rates, making it a suitable installation for homes without the loft space for a tank. 

The energy efficiency of this series is notable as well, with high efficiency ratings contributing to reduced energy consumption and lower utility bills. The convenience of combining heating and hot water in a single appliance with noteworthy flow rates brings forth a solution for households looking to streamline their systems.

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Overview of the Worcester Bosch Greenstar Highflow CDi Series

The Worcester Bosch Greenstar Highflow CDi series stands out with its floor-standing design and high hot water flow rates, catering specifically to larger homes with more than one bathroom.

Distinctive Features

  • Boiler Types: The series comprises two models, the Greenstar Highflow 440cdi and the 550cdi, designed to meet the needs of various household sizes.

  • Hot Water Flow: Both models are celebrated for their exceptional domestic hot water (DHW) flow rates, with the 440cdi offering a rate of 20 litres per minute, whilst the 550cdi can deliver up to 25 litres per minute.

  • Physical Footprint: Unlike wall-hung units, these boilers are floor-standing, usually installed in kitchen or utility areas due to their larger size and weight (exceeding 100 kg).

  • Energy Efficiency: Boasting an 'A' band Efficiency Rating, they operate at around 92% efficiency, contributing to reduced energy consumption and lower bills.

  • LPG Compatibility: For areas without a mains gas supply, both units are LPG convertible, providing versatility in various settings.

Benefits and Drawbacks of a Floor-Standing Boiler


  • Ease of Installation: The design includes a pre-plumbing jig and a wheel-in tray, facilitating a straightforward installation process.

  • High Demand Performance: Ideal for homes with significant hot water requirements, offering consistent and reliable performance.


  • Space Requirements: They require dedicated floor space and are not suitable for wall mounting, which may not be ideal for smaller properties.

  • Weight Considerations: The substantial weight means they must be placed on a solid floor, potentially limiting their placement options.

Key Specifications

This section outlines the essential characteristics of the Worcester Bosch Greenstar CDi Highflow boiler, focusing on its technical specifications and efficiency.

Technical Details

The Greenstar CDi Highflow is a floor-standing combi boiler designed to meet the demands of larger homes with two bathrooms. It boasts a substantially wider 600mm width and 850mm height, with a depth also of 600mm, demanding a significant space for installation.

  • Mounting: Floor-standing

  • Kilowatt (kW) Options: Available in 29.5kW and 41.1kW

  • Flow Rate: Impressive 20 litres per minute

Offering both natural gas and LPG options, this boiler type adapts to various home energy supplies.

Efficiency and Performance

Efficiency is where the Greenstar CDi Highflow combi boiler excels, underscoring Worcester Bosch's commitment to energy-conserving practices.

  • Efficiency Rating: Achieves an A rating for heating under ErP standards

  • Central Heating Output: 92% efficient, contributing to reduced energy bills and eco-friendly operation

This boiler provides instantaneous hot water, an attribute that caters to the high demand of larger homes, while maintaining excellent central heating outputs. With an ERP rating of A for heat and B for water, the appliance is a leader in its class for efficiency.

Design and Installation

The Worcester Bosch Greenstar CDi Highflow boiler is crafted with a pragmatic approach to cater to larger homes. It effortlessly merges high hot water flow rates with a design that eases the installation process.

Boiler Dimensions

The Greenstar CDi Highflow distinguishes itself as a floor-standing boiler, a stark contrast to the more common wall-mounted variants. Its substantial stature is integral to its robust performance. 

Specifically, the boiler is designed to fit snugly within a kitchen or utility room, aligning with the space typically occupied by a washing machine or a similarly sized appliance.

When planning for the installation, it is crucial to acknowledge the following dimensions:

  • Width: Adequate to accommodate the internal components, yet measured to ensure passage through standard door frames.

  • Height: Tall enough to house the high-performance mechanism, while being mindful of typical ceiling heights.

  • Depth: Balancing the internal space for component operation without extruding excessively into the room.

Installation Requirements

Installing the Greenstar CDi Highflow involves a series of specific requirements, designed to ensure both safety and optimal operation. Firstly, as a floor-standing combi boiler, it negates the need for wall mounting, which can pose structural challenges in certain properties. Its built-in wheel-in tray and pre-plumbing jig underscore a commitment to straightforward installation, minimising both time and potential complexities for the engineer.

Key installation considerations are as follows:

  • Gas Supply: Adequate gas pressure is paramount; both natural gas and LPG options necessitate different arrangements.

  • Ventilation: The room must sustain good ventilation to assure efficient and safe combustion.

  • Flue: A suitably positioned flue is essential, adhering to regulations that govern its exit point and clearance from obstructions.

  • Pipework: Neat and precisely planned pipework not only influences the efficiency but also affects the aesthetic after installation.

  • Electrical Connection: A reliable electrical connection is required for the boiler's controls and sensors, requiring meticulous electrical work.

It is imperative that a Gas Safe registered engineer performs the installation to ensure compliance with all safety standards and regulations.

Performance and Efficiency

The Worcester Bosch Greenstar CDi Highflow series stands out for its excellence in both hot water delivery and energy-saving performance. It is a robust solution for homes that have significant demands for heating and hot water daily.

Heating and Hot Water Capabilities

The Highflow series excels in delivering consistent heating and hot water. Notably, it is capable of supplying homes with more than two bathrooms without any noticeable drop in pressure or temperature. 

Industry-leading hot water flow rates are a hallmark of this range, with some models reaching up to 25 litres per minute. This ensures quick and reliable access to hot water, especially during peak demand times.

Energy Efficiency

When it comes to energy efficiency, the Greenstar CDi Highflow is impressive, boasting an 'A' energy efficiency rating. The boiler is designed to convert over 90% of fuel into heat, thus reducing energy waste. 

Also, the ERP (Energy related Products) rating for heat is 'A', ensuring it meets current regulation and high standards for energy efficiency. In terms of hot water, the ratings can vary, with some achieving a 'B' ERP rating, indicating a high level of efficiency in hot water production.

Such efficient use of energy leads to reduced energy bills, making this boiler an energy-saving powerhouse that is aligned with the Energy Saving Trust's recommendations. Users can enjoy a warm home and plentiful hot water, content in the knowledge that their boiler is working in an eco-friendly manner.

Comparative Analysis

When selecting a combi boiler, homeowners often weigh up varied aspects, seeking a balance between robust performance and energy efficiency. 

Particularly, the Worcester Bosch Greenstar CDi Highflow stands out for its suitability in servicing larger homes with substantial hot water demands.

Greenstar CDi Highflow vs Viessmann 222-F

The Worcester Bosch Greenstar CDi Highflow is a well-regarded floor-standing combi boiler, renowned for its impressive hot water flow rates, making it ideal for larger homes with more than one bathroom. It boasts an 'A' band rating for its energy efficiency, reflective of its capability to exceed 90% efficiency for both heating and hot water provision. This boiler integrates a built-in condensate pump to streamline installation and functionality.

In comparison, the Viessmann Vitodens 222-F presents a competitive stance with its space-saving design and also caters to the higher hot water needs of substantial properties. While it shares the Greenstar's high-efficiency ratings, the Vitodens 222-F distinguishes itself with a built-in storage tank, which can deliver hot water rapidly without the need for preheating.

Here's a succinct comparison:


Worcester Bosch Greenstar CDi Highflow

Viessmann Vitodens 222-F


Floor-standing Combi

Combi with Integrated Tank

Energy Efficiency

A Band Rating

A Rated

Central Heating Output

29.2 kW

Similar High-performance

Hot Water Flow Rate

20 litres per minute

High with Storage Tank


Large homes with 2+ bathrooms

Large homes, Fast Hot Water


Heavier due to size

Lighter with compact design

Other Features

Built-in condensate pump

Built-in storage tank

Both boilers require a Gas Safe registered engineer for installation. Their large output capabilities and efficient operation eliminate the need for separate hot water tanks, granting them an edge in the realm of boiler replacement options for sizable, demanding properties.

New Boiler Costs

Boilers can be a daunting purchase for many people as they’re an appliance with a lot of responsibility, providing heat for you and your family is something you want to get right. Boilers aren’t exactly a quickly disposable item either, potentially lasting you a decade.

Boiler costs can be split into two segments: the first is the actual boiler itself (unit price), and the second is the cost of the boiler being installed (set up) in your property by an expert engineer. 

Here at iHeat, we want to remove all of this undue stress and make the decision making process of upgrading to a new central heating system, as easy as possible.

Boiler costs can vary depending on a number of factors including their brand, model, fuel, output, warranty, labour and installation type. Typically a new boiler will cost between £1,845 and £3,500, below is a list of average boiler installations offered by iHeat (guide only).

Installation Type

Price (inc VAT)

Combi to combi swap


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System to combi conversion


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New boiler install


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Back boiler to a combi


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System to system


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Frequently Asked Questions

How long does a Worcester Bosch Greenstar boiler last?

A Worcester Bosch Greenstar boiler typically has a lifespan of 10 to 15 years, provided it is serviced annually and maintained correctly.

Why does my Worcester boiler keep firing up when heating is off?

If a Worcester boiler continues to fire up even when the heating is off, this could be due to issues with the thermostat, external controls, or a sticking diverter valve needing attention.

Why is the pump running constantly on a Greenstar CDi boiler?

The constant running of the pump in a Greenstar CDi boiler might indicate a fault in the boiler's controls or an issue with the pump overrun, which requires diagnosis by a qualified engineer.

What temperature should Greenstar CDi flow?

The recommended flow temperature for a Greenstar CDi is typically between 65°C to 75°C, depending on individual heating requirements and external temperatures.

Are Worcester Greenstar boilers any good?

Worcester Greenstar boilers are well-regarded for their efficiency, reliability, and performance. They often receive positive reviews for their high hot water flow rates and energy-saving features.

How long should a Worcester Greenstar boiler last?

The expected duration for a well-maintained Worcester Greenstar boiler is generally around 10 to 15 years.

Why does my Worcester boiler keep firing up when heating is off?

Frequent unwarranted firing could be a sign that the boiler is attempting to maintain temperature due to incorrect settings or it may be signalling an internal fault that needs to be fixed by a professional.

Stephen Day profile photo
Article by
Stephen Day | Co-founder
Gas Safe registered and FGAS certified engineer with over 20 years experience in the heating and cooling industry.