Worcester Bosch Greenstar 4000 System Boiler Cost with Installation

The Greenstar 4000 is Worcester Bosch’s mid-range system boiler, sitting between the entry-level 2000 and the premium 8000 in the Greenstar lineup. A system boiler heats water and stores it in a separate hot water cylinder, meaning large volumes are available simultaneously to multiple outlets – the key advantage over a combi for homes with two or more bathrooms in regular joint use. 

Available in five outputs from 12kW to 24kW, the 4000 System carries built-in WiFi, a full-colour display, and a 1:10 modulation ratio as standard. The cylinder, flue, and Greenstar System Filter are separate purchases.

Discover more of the Worcester Bosch Greenstar 4000 System specifications below:

Worcester Bosch Greenstar 4000 System Product Table
	Available outputs	12kW	15kW	18kW	21kW	24kW
	Type	System	System	System	System	System
	Fuel	Gas / LPG	Gas / LPG	Gas / LPG	Gas / LPG	Gas / LPG
	Condensing	Yes	Yes	Yes	Yes	Yes
	Efficiency rating (%)	94	94	94	94	94
	ErP	A	A	A	A	A
	LPG compatible	Yes
	Standard guarantee	2 to 10 years*
	Max output (kW)	12	15	18	21	24
	Flow rate (l/min)	Determined by cylinder size
	Mounting	Wall-mounted
	Dimensions (mm)	724 x 400 x 310
	Typical price (incl. VAT)	£1,000	£1,050	£1,100	£1,150	£1,200
	Typical installation cost (incl. VAT)	£1,500
	Total cost	£2,500 – £2,700

*Terms and conditions apply.

Worcester Bosch Greenstar 4000 System overview

The 4000 System replaced the Greenstar i System in May 2021, adding built-in WiFi, a full-colour display, and 1:10 modulation to the well-established i platform. For homes replacing a Greenstar i System, Simple Switch compatibility means the 4000 fits directly in its place with minimal pipework modification.

The trade-off versus a combi is space and upfront cost. The hot water cylinder occupies an airing cupboard or equivalent, and if the property does not already have one, fitting a new cylinder adds £400-£900 to the installation. For homes already running a system boiler, the 4000 System is a straightforward like-for-like upgrade. For homes switching from a combi, the cylinder installation is part of the project and worth discussing with a Gas Safe engineer before committing to a specification.

Worcester Bosch Greenstar 4000 System Range
Model output size	Suitable for	Radiators	Notes
12kW	Small homes, 1-2 bedrooms	Up to 8	Best for properties with lower heat loss
15kW	Small to medium homes, 2-3 bedrooms	Up to 10	Most common for two-bathroom terraces
18kW	Medium homes, 3 bedrooms	Up to 13	Standard family home replacement
21kW	Medium-large homes, 3-4 bedrooms	Up to 16	For properties with higher heat demand
24kW	Large homes, 4+ bedrooms	Up to 20	High-demand family homes with multiple bathrooms

Output selection for a system boiler is based on the heat loss of the property rather than the number of bathrooms – the cylinder size handles hot water capacity separately. A Gas Safe engineer calculates the required boiler output from a property survey. For most three-bedroom homes, the 18kW is the appropriate starting point.

Key benefits at a glance

• ErP A-rated efficiency (94% efficient)
• Built-in WiFi and full-colour text display as standard
• LPG compatible across all outputs
• Internal pump and expansion vessel
• 1:10 modulation ratio
• Quiet Mark certified – 42dB operation
• Simple Switch compatible with Greenstar i System range
• EasyControl app for remote scheduling and energy tracking
• Compatible with Nest, tado, Hive, Amazon Alexa, and Google Home Assistant
• 5-year standard warranty, up to 10 years with Accredited installer and Greenstar System Filter*
• Hydrogen blend ready (up to 20%)

Worcester Bosch Greenstar 4000 System technical specifications

Output and efficiency ratings

All five outputs carry 94% ErP A-rated efficiency. As condensing boilers, they recover heat from exhaust gases that older non-condensing boilers expelled – the same mechanism that applies to a combi, with the difference that the heat charges a stored cylinder rather than delivering hot water directly to the tap.

The 1:10 modulation ratio is the 4000 System’s strongest technical differentiator. At 1:10, a 24kW model can operate as low as 2.4kW under minimal demand, maintaining a stable low flame during mild weather rather than cycling on and off. 

Narrower modulation ratios – common in lower-tier system boilers – force the boiler to shut down entirely when demand falls below its minimum output, increasing component wear and reducing seasonal efficiency.

Dimensions 

At 724mm tall, 400mm wide, and 310mm deep, the 4000 System fits the majority of standard boiler positions. The internal pump and expansion vessel are both housed within the casing, reducing the number of external components the installer needs to position separately. 

Simple Switch compatibility with the Greenstar i System range (i System 2005-2015, i System ErP 2015-2021) means existing pipework connections are reused directly on like-for-like replacements. 

Components included

The full-colour text display provides fault code information in plain text rather than numeric codes, and the boiler’s built-in diagnostics use predictive technology to identify potential issues before they cause breakdowns. 

Built-in WiFi connects to the EasyControl app as standard, with remote temperature adjustment, schedule programming, and energy usage tracking including the consumption impact of changing set temperature by a single degree.

Voice control via Amazon Alexa and Google Home Assistant is supported. Third-party thermostats including Nest, tado, and Hive are compatible via integration.

Prices and installation costs

The Worcester Bosch Greenstar 4000 System costs approximately £1,000 for the 12kW rising to £1,200 for the 24kW, including a standard horizontal side-wall flue. These figures cover the boiler unit only. The hot water cylinder is a separate purchase and installation. Where a vertical roof exit is required, budget £300-£500 in addition. For a broader overview of system boiler costs, see our system boiler cost guide.

These prices assume a like-for-like replacement with an existing cylinder retained, using a mid-range installation figure of £1,500. If your existing cylinder needs replacing, budget an additional £500-£1,000 for a new unvented cylinder plus fitting. If you are switching from a combi and have no cylinder at all, the total project cost rises further still – get a full survey before committing to a price.

Using a mid-range installation figure of approximately £1,500:

Worcester Bosch Greenstar 4000 System Costs
Output size	Unit cost (incl. flue)	Total (incl. installation)
12kW	£1,000	£2,500
15kW	£1,050	£2,550
18kW	£1,100	£2,600
21kW	£1,150	£2,650
24kW	£1,200	£2,700

These prices are indicative only, based on our research and actual boiler prices submitted to WhatPrice by homeowners. 

Warranty and support

The 4000 System carries a 5-year standard warranty, extendable to 10 years when installed by a Worcester Bosch Accredited Installer with a Greenstar System Filter fitted and registered within 30 days. 

Annual servicing by a Gas Safe registered engineer is required to maintain cover. The Greenstar System Filter is not included in the box – budget around £100-£120 and confirm it is in the installation quote.

Worcester Bosch’s national engineer network handles warranty call-outs consistently well in independent surveys. The brand holds a Which? Best Buy recommendation and has done so for over a decade.

Installation information

A like-for-like system boiler replacement on existing pipework can be completed in a day, with labour typically costing around £1,500. 

An installation requiring a new cylinder adds half a day to a full day. The internal pump and expansion vessel simplify the wall-mounted installation relative to a heat-only boiler. 

For Greenstar i System replacements, Simple Switch compatibility means existing pipework connections are reused directly.

What to expect on installation day

Do you need a system flush or filter?

UK Building Regulations require a magnetic filter on any new boiler installation. Fitting a Greenstar System Filter satisfies this requirement and is a condition of the 10-year warranty. It is not included in the box and should be in the installation quote from the outset.

A powerflush is not legally mandated but is strongly recommended on systems over ten years old. Budget £350-£800 depending on the number of radiators.

Finding a Gas Safe registered engineer

All gas boiler installations must be carried out by a Gas Safe registered engineer. For the 10-year warranty, the installer must also hold Worcester Bosch Accredited status. 

If a new unvented cylinder is being fitted, a G3 qualification is additionally required. Confirm all certifications at the quoting stage. 

You can use the WhatPrice quote service to be matched with vetted, Gas Safe registered installers in your area.

Reviews and ratings

Worcester Bosch holds a 4.6 out of 5 rating on Trustpilot UK, based on over 50,000 reviews. The 4000 System draws limited model-specific accounts in the pool:

Positive reviews

The clearest positive account describes a homeowner replacing a 20-year-old Worcester Bosch Greenstar 28 system – changed on age rather than fault, which is a common pattern with the Greenstar system range and a reflection of how long predecessor models tend to run.

The 4000 System is described as compact, neat, and working well several months in, with moderate efficiency improvements expected over time. Like-for-like replacements from the Greenstar i System using Simple Switch compatibility are consistently noted in broader installer feedback as fast, clean installations.

Negative reviews

The most detailed critical account flags the programming and initial setup as unnecessarily complicated. The reviewer spent considerable time with the manual without resolving the configuration, and notes that even the installing engineer had difficulty.

The practical implication: ask your engineer to complete the initial programming before they leave, including scheduling and temperature setpoints, rather than leaving configuration to the homeowner after the fact.

Warranty expectations are the other recurring point of friction in the broader 4000 range. Several owners discover after a fault that the 5-year standard applies rather than the 10-year tier they expected, typically because the Accredited installer or filter registration condition was not met at installation.

How the Worcester Bosch Greenstar 4000 System compares

Worcester Bosch Greenstar 4000 System Comparison Table
Model	Worcester Bosch Greenstar 4000 System	Vaillant ecoTEC plus System	Ideal Logic+ System
Typical unit price (18kW)	£1,100	£1,150	£950
Heat exchanger	Aluminium	Stainless steel	Aluminium
Standard warranty	5 years	5 years	7 year
Max warranty	10 years	10 years	10 years
Built-in WiFi	Yes	No	No
App control	EasyControl (built-in)	vSMART (optional)	Ideal Halo (optional)
Internal pump	Yes	Yes	Yes
Internal expansion vessel	Yes	Yes	Yes
LPG compatible	Yes	Yes	Yes
Max output	24kW	35kW	35kW

For personalised guidance on choosing the right boiler, we recommend speaking with a Gas Safe registered engineer.

Final thoughts – is the Worcester Bosch Greenstar 4000 System right for you?

For homes replacing a Greenstar i System, the 4000 System is the natural choice. Simple Switch compatibility, the same installer network, and a well-established reliability record make it the path of least resistance, and the addition of built-in WiFi, a full-colour display, and 1:10 modulation are meaningful improvements over the i generation.

Against the Vaillant ecoTEC plus, the 4000 System is marginally cheaper at 18kW and includes built-in WiFi that the ecoTEC plus does not carry as standard. The ecoTEC plus uses a stainless steel heat exchanger and offers outputs to 35kW, which matters for larger properties where the 4000 System’s 24kW ceiling becomes a constraint. The Ideal Logic+ System undercuts both on unit price but carries a 1-year standard warranty, substantially shorter than the 4000 System’s 5-year baseline.

The cylinder question remains the most important one for homeowners deciding between a system and combi configuration. Where an existing cylinder is being retained, the 4000 System is a straightforward, well-priced choice. Where a new cylinder is required, the total project cost rises considerably, and a Gas Safe engineer’s assessment of the property’s hot water demand is worth having before committing to the specification.

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