Worcester Bosch Greenstar 4000 Review and Price Guide 2026
Quick Answer: The Worcester Bosch Greenstar 4000 is a mid-range condensing combi and system boiler with 94% efficiency, built-in WiFi, a full-colour display, and a 1:10 modulation ratio. Available as a combi in 25kW and 30kW outputs and as a system boiler in five outputs from 12kW to 24kW. Combi prices start at around £1,250 (parts only), system models from £1,100. Warranty is up to 10 years with annual servicing and a Greenstar System Filter fitted. The 4000 is one of the most installed boilers in the UK and holds a consistent Which? Best Buy recommendation. The Worcester Bosch Greenstar 25i features a compact design, making it ideal for smaller homes where space is at a premium. It boasts an impressive energy efficiency rating and low running costs, contributing to significant savings on energy bills. With its user-friendly interface, homeowners can easily monitor and manage their heating requirements to enhance comfort levels.
The Worcester Bosch Greenstar 4000 replaced the previously best-selling Greenstar i range when it launched in May 2021. That was a bold decision — the Greenstar i had an enormous installed base and a strong reputation — but Worcester Bosch clearly had significant upgrades to justify the change. Built-in WiFi, a Quick Tap feature, a 1:10 modulation ratio, and hydrogen-blend readiness all arrive with the 4000 as standard features that the i range did not offer. This review covers every aspect of the Greenstar 4000 in detail to help you decide whether it is the right boiler for your property. In addition to its impressive capabilities, the Worcester Bosch Greenstar boiler features a range of user-friendly controls that enhance its usability. Homeowners will also appreciate the energy efficiency ratings, which contribute to lower utility bills while minimizing environmental impact. With these innovations, it’s clear that Worcester Bosch aims to meet the evolving needs of modern households.
Worcester Bosch Greenstar 4000: Key Specifications
| Specification | Greenstar 4000 Combi | Greenstar 4000 System |
|---|---|---|
| Available outputs | 25kW, 30kW | 12, 15, 18, 21, 24kW |
| Efficiency | 94% (ErP A-rated) | 94% (ErP A-rated) |
| Modulation ratio | 1:10 | 1:10 |
| Built-in WiFi | Yes | Yes |
| Hydrogen blend ready | Yes (up to 20%) | Yes (up to 20%) |
| Dimensions | 710 x 400 x 310mm | 710 x 400 x 310mm |
| Maximum warranty | 10 years | 10 years |
| Noise level | 45dB | 45dB |
Greenstar 4000 Combi Boiler Models
25kW Combi
The 25kW model is designed for smaller properties with up to 10 radiators and a single bathroom. It delivers a hot water flow rate of 10.5 litres per minute — sufficient for a single shower or bath without simultaneous demand from other outlets. For a one or two-bedroom property with a single bathroom, the 25kW is correctly specified and avoids the inefficiency of an oversized boiler short-cycling in a small heating circuit.
30kW Combi
The 30kW version is the more popular model and is suitable for small to medium-sized properties with up to 16 radiators and two bathrooms. The increased output raises the hot water flow rate to 12.3 litres per minute, giving it the capacity to manage higher simultaneous demand more comfortably. For most three-bedroom homes with two bathrooms, the 30kW is the appropriate choice. It is consistently one of the best-selling individual boiler models in the UK.
Combi Prices (Parts Only)
| Model | Price (Parts Only) |
|---|---|
| Greenstar 4000 25kW Combi | £1,250 |
| Greenstar 4000 30kW Combi | £1,350 |
Installation costs are additional and will depend on the complexity of the installation, whether flue extensions or system modifications are required, and regional labour rates. Full installed prices including parts and labour typically start from around £1,800 for a straightforward like-for-like replacement.
Greenstar 4000 System Boiler Models and Prices
The system boiler variant suits larger properties with higher hot water demand — homes with two or more bathrooms where a combi’s simultaneous output limitation would be noticeable. The system boiler works with a separate hot water storage cylinder, allowing large volumes of hot water to be available immediately to multiple outlets simultaneously.
Five output options give the 4000 system boiler a wide range of appropriate applications, from a compact 12kW suitable for smaller properties that want the advantages of stored hot water, to a 24kW model for larger family homes.
| Model | Price (Parts Only) |
|---|---|
| Greenstar 4000 System 12kW | £1,100 |
| Greenstar 4000 System 15kW | £1,150 |
| Greenstar 4000 System 18kW | £1,200 |
| Greenstar 4000 System 21kW | £1,250 |
| Greenstar 4000 System 24kW | £1,300 |
Key Features Explained
Built-In WiFi and Smart Controls
The Greenstar 4000 includes built-in wireless connectivity as standard, enabling control via the Worcester Bosch EasyControl app from anywhere with an internet connection. The app allows remote temperature adjustment, schedule programming, and energy usage tracking — including the ability to see the impact on energy consumption of changing the set temperature by a single degree. The 4000 is also compatible with third-party smart thermostats including Nest, tado°, and Hive, giving homeowners flexibility to integrate it with an existing smart home setup or a preferred thermostat platform.
Voice control through Amazon Alexa and Google Home Assistant is supported, and thermostatic radiator valves connected to the EasyControl system allow individual room temperature control from the app — a significant usability upgrade over conventional TRV operation.
1:10 Modulation Ratio
The 4000’s 1:10 modulation ratio is one of its most technically significant specifications. The boiler can reduce its output to just 10% of its maximum capacity — meaning a 30kW model can operate at as little as 3kW when heating demand is low. This prevents the short-cycling that occurs in less sophisticated boilers when demand is low — where the boiler repeatedly fires at full output, satisfies the thermostat quickly, and switches off, only to repeat the cycle minutes later. Short-cycling wastes fuel and accelerates component wear. A wide modulation range allows the boiler to fire continuously at a low, matched output, which is both more efficient and gentler on the heat exchanger and burner components.
Quick Tap
Quick Tap addresses one of the most common complaints about combi boilers — the delay between opening the hot water tap and receiving hot water while the cold water in the pipework is displaced. The feature works by using the first brief opening and closing of the tap as a signal to the boiler that hot water will shortly be needed. The boiler preheats the heat exchanger in response, so that when the tap is opened again approximately 20 seconds later, hot water arrives almost immediately. This reduces both the waiting time and the volume of cold water wasted while waiting for the heat to reach the tap.
Intelligent Filling System
Available on the combi version (not system), the intelligent filling system automatically monitors boiler pressure and opens the internal filling valve to restore pressure when it drops below the optimal level, then closes it again when the correct pressure is reached. If the pressure drop is significant enough to suggest a system leak rather than normal gradual pressure loss, the system alerts the homeowner rather than continuing to add water indefinitely. This feature removes the need for manual repressurisation via the external filling loop for routine pressure maintenance, though a filling key is required if the intelligent filling feature is not specified.
Quiet Operation
The 4000 operates at 45dB — significantly quieter than a normal conversation at 65dB and less than two-thirds the noise level of a vacuum cleaner at 75dB. This makes it well suited to installations in kitchens and utility rooms where the boiler is within everyday living spaces, and effectively inaudible from adjacent rooms during normal operation.
Full-Colour LCD Display
The full-colour text display with push-button controls provides clear status information, diagnostic messages, and straightforward programming access directly from the boiler front panel. When a fault code is displayed, the coloured screen provides more immediately legible information than the simpler LED indicators found on basic boiler models — useful at the point when clear information is most needed.
Simple Switch Installation
For homes replacing an existing Worcester Bosch Greenstar i series boiler, the 4000 is designed to fit directly in its place with minimal pipework modification. The Simple Switch compatibility covers the Greenstar i Junior combi (2005–2015), Greenstar Si combi (2005–2013), Greenstar i ErP (2015–2021), Greenstar i System (2005–2015), and Greenstar i System ErP (2015–2021). This significantly reduces installation time and cost on like-for-like replacements within the Worcester Bosch range. Additionally, the Worcester Bosch Greenstar 8000 efficiency model offers enhanced energy-saving features, making it an excellent choice for eco-conscious homeowners. Its high performance complements the existing range, ensuring consistent quality and reliability across installations. With this option, users can enjoy a modern solution that contributes to lower energy bills and a reduced carbon footprint. The Worcester Bosch Greenstar 8000 features advanced technology that optimizes energy efficiency while providing reliable performance. Homeowners can enjoy the benefits of improved heating capabilities along with reduced energy bills. Additionally, the design ensures a quiet operation, making it an excellent choice for any household.
Efficiency
Both combi and system variants of the Greenstar 4000 achieve 94% efficiency and an ErP A rating. At 94%, 6p of every £1 spent on gas is lost through the flue rather than converted into useful heat — compared to 20p to 40p per £1 for older non-condensing boilers operating at 60 to 80% efficiency. The Boiler Plus legislation requires all new gas boilers in England to achieve a minimum 92% efficiency, so the 4000’s 94% sits comfortably above the regulatory minimum without quite reaching the 98% peak efficiency of premium models such as the Viessmann Vitodens 200-W.
Hydrogen Blend Readiness
The Greenstar 4000 is certified ready for a hydrogen-natural gas blend of up to 20% out of the box. This is relevant to the UK’s long-term decarbonisation trajectory — the government and gas network operators are exploring hydrogen blending as a transitional measure ahead of potential full hydrogen conversion of the gas grid. A blend of up to 20% hydrogen requires no modification to current boilers certified for this blend, meaning any Greenstar 4000 installed today is protected against the first stage of grid hydrogen introduction without requiring any component changes.
Warranty
The Greenstar 4000 warranty is structured around the installation specification and ongoing maintenance.
| Warranty Condition | Duration |
|---|---|
| Standard guarantee | 7 years |
| With Greenstar System Filter fitted | 8 years |
| With System Filter and £150 payment | 10 years |
All warranty tiers require the boiler to be installed by a Gas Safe registered engineer, registered with Worcester Bosch within 30 days of installation, installed in a domestic property, and serviced annually by a Gas Safe engineer. Missing any annual service invalidates the extended warranty and reverts coverage to the standard statutory terms.
The aluminium heat exchanger — noted by heating engineers as the one component specification that falls short of the premium stainless steel heat exchangers found in the Worcester 8000 and Viessmann Vitodens ranges — is fully covered under the warranty, and Worcester Bosch’s backing of a 10-year term on a boiler with an aluminium heat exchanger reflects their confidence in the component’s longevity within a correctly maintained system. When considering a Worcester Bosch boiler price overview, it’s essential to factor in the long-term savings associated with energy efficiency. Although the initial investment may be higher compared to other brands, the durability and warranty provided make it a valuable option for homeowners. Potential buyers should also take into account the overall performance and customer satisfaction ratings that contribute to the brand’s strong reputation in the market.
Greenstar 4000 vs 8000
The most common question from buyers considering Worcester Bosch is whether to choose the 4000 or the 8000. The 8000 is Worcester Bosch’s premium range — it features a stainless steel heat exchanger, a larger physical footprint, and a higher price point. For most small to medium-sized homes where the 4000’s output range is correctly matched to the property’s demand, the additional cost of the 8000 is difficult to justify on performance grounds — the efficiency difference is marginal and the practical heating output difference is negligible for appropriate applications.
The 8000 is the better choice for larger properties, higher hot water demand scenarios, or where the stainless steel heat exchanger specification is a priority consideration for long-term reliability. For the typical UK three-bedroom home, the 4000 30kW delivers everything required at a meaningfully lower price.
Should You Buy the Worcester Bosch Greenstar 4000?
The Greenstar 4000 sits in a strong position in the mid-range market. It offers genuinely useful technology — built-in WiFi, Quick Tap, intelligent filling, and a 1:10 modulation ratio — at a price point that is competitive for a Worcester Bosch product. The Which? Best Buy endorsement, the consistently strong installer recommendation, and the 4.6-star Trustpilot rating that Worcester Bosch maintains reflect a product that performs reliably in real-world installations. The Worcester Bosch Greenstar 1000 features advanced engineering designed for optimal efficiency and durability. With its compact size and user-friendly controls, it caters to a wide range of heating needs, making it an ideal choice for homeowners seeking quality. Additionally, its seamless integration with smart home systems allows for enhanced management and monitoring of energy usage.
The aluminium heat exchanger is the one specification that draws comment from engineers, and it is a legitimate consideration compared to premium alternatives. For a homeowner prioritising value within the Worcester Bosch range, the 4000 delivers a compelling package. For a homeowner wanting the absolute best specification regardless of cost, the 8000 or a Viessmann Vitodens represents the next tier.
FAQ
How efficient is the Worcester Bosch Greenstar 4000?
Both combi and system variants achieve 94% efficiency with an ErP A rating. This means 94p of every £1 spent on gas is converted to useful heat, with just 6p lost through the flue. This exceeds the UK’s Boiler Plus minimum efficiency requirement of 92% and represents a substantial improvement over older non-condensing boilers operating at 60 to 80% efficiency.
What size Greenstar 4000 do I need?
The 25kW combi suits smaller homes with up to 10 radiators and a single bathroom. The 30kW combi suits homes with up to 16 radiators and two bathrooms. For larger homes or properties with higher simultaneous hot water demand, the system boiler range — from 12kW to 24kW — provides stored hot water that removes the simultaneous demand limitation of a combi. A heating engineer can confirm the correct output for the specific property during a survey.
How long is the Greenstar 4000 warranty?
Up to 10 years with a Greenstar System Filter fitted, payment of the extended warranty fee, annual servicing by a Gas Safe engineer, registration within 30 days of installation, and installation by a Gas Safe registered engineer. The standard warranty without these conditions is 7 years.
Is the Greenstar 4000 compatible with smart thermostats?
Yes. The 4000 includes built-in WiFi and is compatible with Worcester Bosch EasyControl, Nest, tado°, and Hive. It also supports Amazon Alexa and Google Home Assistant voice control. The built-in wireless connectivity means no additional receiver hardware is required for basic smart control operation.
What replaced the Worcester Bosch Greenstar i?
The Greenstar 4000 directly replaced the Greenstar i range in May 2021. It is designed as a drop-in replacement for all Greenstar i and Si models from 2005 onwards through Worcester Bosch’s Simple Switch programme, minimising installation time and cost when upgrading from an older Greenstar i installation.
Conclusion
The Worcester Bosch Greenstar 4000 is a well-engineered, genuinely capable mid-range boiler that justifies its market-leading installation volume. The 94% efficiency, 1:10 modulation ratio, built-in WiFi, Quick Tap, and intelligent filling system represent meaningful practical improvements over the Greenstar i it replaced, and the Which? Best Buy endorsement and strong engineer recommendation base reflect consistent real-world performance. These attributes contribute to impressive Worcester Bosch boiler efficiency ratings, making it an excellent choice for homeowners seeking cost-effective heating solutions. Additionally, its advanced features not only enhance user experience but also promote energy conservation, aligning with modern sustainability goals. By choosing the Greenstar 4000, consumers can expect both efficiency and reliability in their heating systems.
For small to medium-sized UK homes — the application for which the combi range is specifically designed — the 30kW model offers everything the vast majority of homeowners will need. The 10-year warranty with correct maintenance provides long-term coverage at a mid-range price point that makes the Greenstar 4000 one of the most straightforward boiler recommendations in the current market.
