Worcester Greenstar 24i Junior Manual: A Comprehensive Guide
This manual details the operation, installation, and maintenance of the Worcester Greenstar 24i Junior boiler, ensuring efficient heating and hot water provision.
The Worcester Greenstar 24i Junior is a highly efficient, compact combi boiler designed for homes with moderate heating and hot water demands. This boiler, manufactured by Worcester Bosch, is renowned for its reliability and user-friendly operation. It’s a popular choice for smaller properties, apartments, and homes with one bathroom.
Located in the historic city of Worcester, alongside renowned establishments like Royal Worcester Porcelain and Berrows Journal, Worcester Bosch has a long-standing reputation for quality engineering. The 24i Junior boasts a modern design and incorporates advanced technology to deliver consistent performance and energy savings. This manual provides comprehensive guidance for installation, operation, maintenance, and troubleshooting, ensuring optimal performance and longevity of your heating system. Understanding its features is key to efficient home comfort.
Understanding the Boiler’s Key Features
The Worcester Greenstar 24i Junior features a high-efficiency condensing heat exchanger maximizing fuel usage and reducing emissions. Its compact design allows for flexible installation options, even in smaller spaces. The boiler offers a modulated output of up to 24kW, adapting to your heating and hot water needs.
A user-friendly digital interface provides clear information and simple controls. The integrated frost protection safeguards against freezing temperatures, crucial in regions like Worcestershire with colder seasons. Furthermore, compatibility with smart thermostats enhances control and energy efficiency. Like the historic city of Worcester, blending old and new, this boiler combines proven technology with modern convenience, offering reliable performance and long-term value.

Installation and Setup
Proper installation by a Gas Safe registered engineer is vital, adhering to regulations and ensuring safe, efficient operation of the Greenstar 24i Junior boiler.
Initial Installation Checks
Before commissioning the Greenstar 24i Junior, several crucial checks must be performed. Verify the boiler’s location complies with regulations, ensuring adequate ventilation and accessibility for servicing. Inspect the gas supply pipework for leaks, utilizing appropriate leak detection fluid. Confirm the electrical supply matches the boiler’s requirements and is correctly earthed.
Thoroughly examine the condensate pipework for any obstructions or damage, ensuring a proper fall for drainage. Check the flue connection is secure and correctly positioned, adhering to manufacturer’s guidelines. Confirm all safety devices are functioning correctly, including the carbon monoxide detector. Finally, ensure the central heating system is properly filled and bled, achieving the correct operating pressure before initial start-up. Document all checks for future reference.
Gas Supply Requirements
The Worcester Greenstar 24i Junior is designed for natural gas (G20) operation. The meter supplying the boiler must be sized correctly to handle the appliance’s gas consumption rate, ensuring adequate flow during peak demand. Gas supply pressure must fall within the specified range – typically 20 mbar.
Existing gas pipework should be inspected for corrosion, leaks, and suitability for the new boiler. Any necessary upgrades or modifications must be carried out by a Gas Safe registered engineer. A gas tightness test must be performed after any pipework alterations. Ensure the gas supply is adequately protected from physical damage and environmental factors. Proper ventilation is crucial in the boiler’s location to prevent gas accumulation.
Condensate Pipe Installation
The Worcester Greenstar 24i Junior produces acidic condensate as a byproduct of its high efficiency operation, requiring a dedicated condensate drain. This pipe must be installed with a downward slope throughout its entire length to ensure proper drainage and prevent blockages. Use appropriate, corrosion-resistant PVC-U pipe of the correct diameter, as specified in the installation guide.
The condensate pipe should terminate in a suitable location, allowing for safe discharge and avoiding potential damage to building materials. Avoid long horizontal runs and ensure the pipe is adequately insulated if exposed to freezing temperatures to prevent freezing. A trap should be installed to prevent flue gases from being drawn back into the boiler.
Flue Installation Guidelines
Correct flue installation is critical for the safe and efficient operation of the Worcester Greenstar 24i Junior. The flue system must conform to all relevant building regulations and be installed by a qualified Gas Safe registered engineer. Ensure the flue is of the correct type and diameter, as specified in the boiler’s installation instructions.
Maintain appropriate clearances to combustible materials and structural openings. The flue terminal must be positioned to prevent the re-entry of flue gases into the property or neighboring buildings. Proper sealing of flue components is essential to prevent carbon monoxide leakage. Regularly inspect the flue for damage or corrosion.

Operating the Greenstar 24i Junior
This section guides users through powering on, controlling temperature settings, and utilizing the timer function for efficient heating and hot water management.
Powering On and Initial Setup
Before initial operation, verify the boiler has been correctly installed by a Gas Safe registered engineer. Ensure the gas and electricity supplies are connected and functioning as expected. To power on, locate the power switch – typically found on the front panel – and toggle it to the ‘on’ position.
The Greenstar 24i Junior will initiate a self-diagnostic check, indicated by the display panel illuminating and cycling through various tests. Allow this process to complete uninterrupted. Following the self-check, the boiler will typically display the current time and temperature; If the time is incorrect, refer to the control panel section for instructions on adjusting it.
Initial setup may involve setting the heating schedule and hot water parameters to suit your preferences. Familiarize yourself with the control panel’s functions for optimal performance.
Understanding the Control Panel
The Greenstar 24i Junior’s control panel features a digital display and several buttons for operation. The display shows current temperature settings, time, and any error codes. Key buttons include the power button, temperature adjustment (+/-), mode selection (heating, hot water, off), and timer/schedule settings.
The ‘i’ button provides access to information and settings, while the reset button is used to acknowledge error messages or restart the boiler. Familiarize yourself with the icons displayed – a flame indicates active heating, a tap signifies hot water demand, and a snowflake represents frost protection.
Navigating the menu allows customization of parameters like heating curves and hot water temperature limits. Refer to the detailed menu guide within this manual for specific instructions on each function.
Setting the Temperature
Adjusting the heating temperature is straightforward using the ‘+’ and ‘-’ buttons on the control panel. The current setpoint is displayed digitally. Separate temperature settings exist for heating and hot water; ensure you’re adjusting the correct one. The boiler allows for precise temperature control, typically ranging from 55°C to 80°C for heating and 40°C to 60°C for hot water.
Consider energy efficiency when setting temperatures. Lowering the heating temperature by even 1°C can result in significant savings. Utilize the boiler’s pre-set programs or create custom schedules to match your lifestyle.
Remember to allow sufficient time for temperature changes to take effect, and avoid frequent adjustments for optimal performance.
Using the Timer Function
The Greenstar 24i Junior features a built-in timer for automated heating control. Access the timer settings through the control panel’s menu, navigating with the selector button and confirming with the ‘Enter’ button. You can program different time periods with specific temperatures for each day of the week.
The timer allows for up to three heating periods per day: morning, afternoon, and evening. Setting a schedule ensures comfort when needed and reduces energy consumption during unoccupied times. Explore pre-set programs or create a personalized schedule tailored to your routine.
Ensure the correct time and date are set for accurate timer operation.

Maintenance and Troubleshooting
Regular maintenance, including descaling and servicing, is crucial for optimal performance. This section details common issues, error codes, and solutions for your boiler.
Regular Servicing Requirements
Annual servicing by a qualified Gas Safe registered engineer is essential to maintain the efficiency and safety of your Worcester Greenstar 24i Junior boiler. This comprehensive check ensures all components are functioning correctly, preventing potential faults and maximizing lifespan. The service includes a visual inspection, flue analysis, and cleaning of key parts, like the burner and heat exchanger.
Regular servicing also helps identify minor issues before they escalate into costly repairs. It’s a legal requirement in many instances and validates your boiler’s warranty. Ignoring servicing can lead to reduced efficiency, increased fuel bills, and potentially dangerous carbon monoxide emissions. A documented service history is vital for peace of mind and future maintenance.
Contact a Gas Safe registered engineer today to schedule your annual service and ensure your heating system operates safely and efficiently throughout the year.
Descaling the Boiler
Over time, limescale can build up within the Worcester Greenstar 24i Junior boiler, reducing its efficiency and potentially causing damage. Descaling removes these mineral deposits, restoring optimal performance and extending the boiler’s lifespan. The frequency of descaling depends on water hardness in your area; harder water requires more frequent attention.
It’s highly recommended to have a qualified engineer perform the descaling process as it involves specialized equipment and chemicals. Attempting to descale the boiler yourself could void the warranty and cause irreversible damage. A professional will safely flush the system with a descaling solution, then thoroughly rinse it to remove any residue.
Regular descaling contributes to lower energy bills and a more reliable heating system. Discuss a descaling schedule with your engineer during your annual service.
Error Codes and Their Meanings
The Worcester Greenstar 24i Junior boiler utilizes error codes to diagnose potential issues. These codes are displayed on the control panel, providing valuable information for troubleshooting. Understanding these codes can help you identify the problem before calling a qualified engineer. Common codes include E16 (low water pressure), E11 (flame sensing issue), and E28 (pump fault).
Refer to the full error code list in the boiler’s manual for a comprehensive explanation of each code and suggested actions. Do not attempt to repair the boiler yourself based solely on the error code; always consult a Gas Safe registered engineer for any repairs.
Ignoring error codes can lead to further damage and potential safety hazards. Promptly addressing the issue ensures efficient and safe operation.
Low Pressure Issues and Solutions
Low water pressure is a common issue with the Worcester Greenstar 24i Junior boiler, often indicated by the E16 error code. This can be caused by a leak in the system, air trapped within the radiators, or a faulty pressure relief valve. Before attempting any solutions, ensure the boiler has cooled down.
To address low pressure, first locate the filling loop and carefully repressurize the system to the recommended 1-1.5 bar. Bleed any air from the radiators to improve circulation. If the pressure continues to drop, inspect the system for leaks, checking radiators, pipes, and the boiler itself.
If you are uncomfortable performing these steps, or the problem persists, contact a qualified Gas Safe registered engineer.
Frozen Condensate Pipe – Prevention and Thawing
During cold weather, the condensate pipe of your Worcester Greenstar 24i Junior can freeze, causing the boiler to shut down as a safety precaution. Prevention is key: insulate exposed pipework, especially in unheated areas, and ensure adequate ventilation. Avoid pouring hot water directly onto a frozen pipe, as this can cause it to burst.
To thaw a frozen pipe, gently warm it with a hairdryer on a low setting, starting from the boiler end and working outwards. Alternatively, wrap the pipe with warm (not hot) towels. Never use a naked flame or direct heat source.
If you cannot safely thaw the pipe, contact a qualified engineer.

Safety Features and Precautions
The Greenstar 24i Junior incorporates vital safety mechanisms, including carbon monoxide detection and automatic shut-off features, prioritizing user well-being.
Carbon Monoxide Detection
The Worcester Greenstar 24i Junior boiler is equipped with a sophisticated carbon monoxide (CO) detection system, a crucial safety feature. This system continuously monitors flue gases for the presence of this odorless, colorless, and potentially fatal gas. Should dangerous levels of CO be detected, the boiler will immediately shut down, preventing further emission and safeguarding occupants.
Regular servicing by a qualified Gas Safe engineer is paramount to ensure the CO detector’s functionality. The engineer will test the detector’s responsiveness and verify the integrity of the entire flue system. Never ignore any signs of potential CO poisoning, such as headaches, dizziness, nausea, or flu-like symptoms. Install a separate, audible CO alarm in your home for an additional layer of protection, positioned away from the boiler itself.
Boiler Safety Checks
Prior to operating the Worcester Greenstar 24i Junior, perform routine safety checks. Visually inspect the boiler casing for any damage or obstructions. Ensure the flue is clear of debris and properly connected, preventing dangerous fume emissions. Verify the gas supply connection is secure and free from leaks – never attempt repairs yourself; contact a Gas Safe registered engineer.
Regularly check the condensate pipe for blockages, especially during colder months, as freezing can cause issues. Confirm the boiler pressure is within the recommended range, indicated on the control panel. Annual servicing by a qualified professional is essential for comprehensive safety assessments, including combustion analysis and component inspections. Do not bypass any safety devices or attempt modifications.
Emergency Shut-Off Procedures
In an emergency, immediately shut off the gas supply to the Worcester Greenstar 24i Junior. Locate the gas isolation valve, typically near the boiler, and turn it to the ‘off’ position. If you smell gas, do not operate any electrical switches – open windows and doors to ventilate the area and evacuate the premises. Contact the gas emergency services from a safe location.
To power down the boiler, use the control panel’s on/off switch. Familiarize yourself with its location beforehand. If the boiler displays an error code indicating a critical fault, switch it off and consult a Gas Safe registered engineer. Never attempt to repair the boiler yourself during an emergency. Ensure all occupants are aware of these procedures for swift and safe response.

Advanced Features
The Greenstar 24i Junior offers smart thermostat compatibility for remote control and optimized efficiency, alongside features designed to minimize energy consumption and costs.
Smart Thermostat Compatibility
The Worcester Greenstar 24i Junior is designed to seamlessly integrate with a range of smart thermostats, offering homeowners enhanced control and convenience over their heating systems. Compatibility extends to popular brands, allowing for remote operation via smartphone apps, providing adjustments to temperature settings from anywhere with an internet connection.

This connectivity enables the creation of personalized heating schedules, optimizing comfort and reducing energy waste. Smart thermostats learn household routines, automatically adjusting temperatures to suit occupancy patterns. Furthermore, integration often provides detailed energy usage reports, empowering users to identify areas for further savings. The ability to monitor and manage the boiler remotely also offers peace of mind, particularly during colder months or when away from home for extended periods.
Boiler Efficiency and Energy Saving Tips
Maximizing the efficiency of your Worcester Greenstar 24i Junior is key to reducing energy consumption and lowering heating bills. Regular servicing, as outlined in this manual, ensures optimal performance. Avoid excessively high flow rates for hot water, as this can strain the boiler and reduce efficiency.
Insulating hot water pipes and radiators minimizes heat loss, further enhancing energy savings. Utilize the boiler’s timer function to schedule heating only when needed, avoiding unnecessary operation during unoccupied periods. Consider a smart thermostat for advanced scheduling and remote control. Bleeding radiators regularly removes trapped air, improving heat circulation. Finally, ensure the boiler is not obstructed by furniture or other items, allowing for adequate ventilation and efficient operation.

Technical Specifications
This section provides detailed technical data for the Worcester Greenstar 24i Junior, including dimensions, weight, gas consumption, and required water pressure levels.
Boiler Dimensions and Weight
Understanding the physical specifications of the Greenstar 24i Junior is crucial for installation planning and ensuring adequate space allocation. The boiler’s compact design facilitates installation in various property types, including those with limited space. Typically, the unit measures approximately 700mm in height, 390mm in width, and 290mm in depth. These dimensions are approximate and should be verified with the official installation guide for precise measurements.
Regarding weight, the Greenstar 24i Junior generally weighs around 60 kilograms. This weight is a significant consideration when determining appropriate mounting and support structures. Proper handling procedures are essential during installation to prevent damage or injury. Always consult a qualified Gas Safe registered engineer for installation and ensure the supporting wall or surface can safely bear the boiler’s weight. Accurate dimensions and weight are vital for a successful and safe installation.
Gas Consumption Rates
Understanding the gas consumption rates of the Greenstar 24i Junior is essential for estimating running costs and ensuring the gas supply adequately meets demand. The boiler’s consumption varies based on heating output and hot water draw-off. At maximum heating output, the unit typically consumes around 2.4 kg/h of natural gas. For hot water production, the consumption rate is approximately 1.8 kg/h, depending on the desired water temperature and flow rate.
These figures are approximate and can fluctuate based on factors like ambient temperature and system efficiency. It’s crucial to refer to the official Worcester Bosch documentation for precise consumption data specific to your installation. Monitoring gas usage can help identify potential inefficiencies and optimize boiler performance. Regular servicing ensures the boiler operates at its designed efficiency, minimizing gas consumption and reducing energy bills.

Water Pressure Requirements
Maintaining correct water pressure is vital for the optimal performance of the Worcester Greenstar 24i Junior boiler; The recommended incoming water pressure should be between 1.0 and 8.0 bar (14.5 – 116 psi). Pressures outside this range can cause operational issues, including reduced hot water flow or boiler shutdown. Low pressure may indicate a system leak or insufficient mains pressure, requiring investigation by a qualified Gas Safe engineer.
High pressure can damage components within the boiler and central heating system. A pressure relief valve is incorporated to mitigate excessive pressure, but consistent high readings necessitate professional attention. Regularly check the boiler’s pressure gauge and familiarize yourself with the acceptable range. Ensuring adequate water pressure guarantees efficient heating and hot water delivery throughout your home.

Resources and Support
Access official manuals, find certified engineers via Gas Safe Register, and explore warranty details on the Worcester Bosch website for assistance.
Worcester Bosch Official Website
The official Worcester Bosch website (www.worcester-bosch.co.uk) serves as the primary hub for all Greenstar 24i Junior related resources. Here, you can directly download the comprehensive user manual in PDF format, ensuring you have the latest version readily available. Beyond the manual, the website provides a wealth of supporting documentation, including installation guides, servicing checklists, and frequently asked questions addressing common issues.
Furthermore, the site features a dedicated support section where you can register your boiler for warranty purposes and access troubleshooting guides. Interactive tools, such as parts diagrams and a boiler locator, are also available. You’ll find contact information for their customer service team, allowing you to reach out for personalized assistance if needed. The website is regularly updated with important safety notices and product information.
Finding a Qualified Gas Safe Engineer
For any installation, servicing, or repair work on your Worcester Greenstar 24i Junior, it is crucial to employ a Gas Safe registered engineer. The Gas Safe Register (www.gassaferegister.co.uk) is the official list of qualified and competent gas engineers in the UK. Using an unregistered engineer is illegal and incredibly dangerous, potentially leading to gas leaks, carbon monoxide poisoning, and invalidating your boiler’s warranty.
The Gas Safe Register website allows you to search for local engineers by postcode. Always verify their credentials on the register before allowing them to work on your boiler. Ensure they are specifically qualified to work with domestic gas boilers. Request references and check online reviews to assess their reputation and quality of work. A qualified engineer will provide a Gas Safety Certificate upon completion of any gas work.
Warranty Information
The Worcester Greenstar 24i Junior boiler comes with a standard manufacturer’s warranty, typically covering parts and labour for a specified period. The length of the warranty can vary depending on the installation date and any promotional offers available at the time of purchase. It’s essential to register your boiler with Worcester Bosch promptly after installation to activate the full warranty coverage.
To validate your warranty, annual servicing by a Gas Safe registered engineer is usually a mandatory requirement. Keep records of all servicing and repair work undertaken. The warranty does not cover issues arising from incorrect installation, improper use, scale buildup due to hard water, or lack of regular maintenance. Refer to the full warranty terms and conditions document provided with your boiler for complete details.
















































































