The Worcester Bosch Greenstar 4000 30kW is Worcester’s current mid-range gas combi and the model most people mean when they search for a “Worcester Bosch combi 30”. It suits flats and two to three bedroom homes with one bathroom, giving around 12.3 litres of hot water a minute at a 35°C rise.
It replaced the popular Greenstar 30i, which is now discontinued, and it’s still on sale in 2026. Below, we go through the specs, running costs, installation prices and alternatives to help you decide if it’s right for your home.
What Are The Greenstar 4000 30kW’s Key Specs?
It’s a 30kW gas combi with 24kW for heating, 12.3 l/min of hot water at a 35°C rise and an A rating for heating and hot water.
| Specification | Greenstar 4000 30kW combi |
| Boiler type | Wall-hung gas condensing combi |
| Hot water output | 30kW |
| Central heating output | 24kW |
| Hot water flow rate | 12.3 l/min at 35°C rise |
| ErP rating | A for heating, A for hot water |
| Dimensions (H x W x D) | 724 x 400 x 310mm |
| Fuel | Natural gas or LPG |
| Maximum flue length | Up to 12m (60/100 flue) |
| Status | Current model in 2026; replaced the discontinued Greenstar 30i |
What Is The Worcester Bosch Greenstar 4000?
It’s Worcester’s mid-range combi, launched in 2021 to replace the Greenstar i range, which had been one of the UK’s best-selling combis for years.
Worcester kept the parts of the Greenstar i that installers liked and updated the rest. You get a full colour display, better flue options and a water-saving hot water mode.
The range comes in two combi sizes, 25kW and 30kW, plus system boiler versions. The 30kW is the more popular combi of the two, because it gives you a stronger shower without moving up to a much bigger boiler.
There’s also a practical detail that helps when you’re replacing an older Worcester. The 4000 follows Worcester’s SimpleSwitch approach, so its fixing points and pipe centres line up with many Worcester boilers fitted between 2005 and 2015.
That often means less pipework to alter and a quicker installation day.
What Features Does The Greenstar 4000 30kW Have?
The headline features are a colour display, a water-saving Quick Tap mode and a larger condensate siphon that’s less likely to freeze.
- Colour display. The front panel uses a clear full colour text display, so settings and fault messages are easier to read than on older Greenstar models.
- Quick Tap. This mode stops the boiler firing for very short taps, like rinsing a cup, which cuts down on wasted gas and water.
- Good in low pressure areas. Worcester says the 4000 performs well where mains water pressure is on the low side.
- Quiet running. It’s one of the quieter combis on the market, which matters if it sits in a kitchen or near a bedroom.
- Larger condensate siphon. A 500ml siphon reduces the risk of the condensate pipe freezing in a cold snap.
- Smart controls. It works with Bosch EasyControl and most third-party smart thermostats. Our smart thermostats page covers the options.
How Efficient Is The Greenstar 4000 30kW?
It’s ErP A-rated for heating and hot water, and Worcester quotes around 94% efficiency for the range.
Its wide modulation range lets it turn itself down on milder days instead of switching on and off, and that saves gas. But as with any condensing combi, your running costs come down to how it’s set up.
We usually set the radiator flow temperature at around 55 to 60°C and pair the boiler with a weather or load compensating control. A system flush and a magnetic filter at installation also help it keep its efficiency over time.
If you’re swapping out an old non-condensing boiler, the savings can be substantial. Replacing a Greenstar 30i or another condensing combi over 8 years old is different: expect a smaller saving, with the bigger gain coming in reliability and features.
What Are The Pros And Cons Of The Greenstar 4000 30kW?
It gives strong hot water for its size and swaps easily for older Worcesters, but it can’t really run two showers at once.
Pros
- Strong hot water flow for a mid-size combi
- Compact enough for most kitchen cupboards
- Clear colour display and simple controls
- Fixing points match many older Worcester boilers, which can make replacement simpler
- Long flue options give you more freedom over where it goes
- Natural gas and LPG versions available
Cons
- Costs more than budget brands with similar outputs
- Not suited to homes with two bathrooms used at the same time
- 24kW heating output limits it in larger or poorly insulated homes
- Hot water performance depends on your mains pressure and flow
What Size Home Does The Greenstar 4000 30kW Suit?
It suits flats, terraces and semis with one bathroom and up to around 10 to 12 radiators.
A shower and the kitchen tap running together is fine. Two showers at once will struggle.
If you’ve got a busy household with an en-suite, the Greenstar 36CDi Compact or a Greenstar 8000+ is a better match. For a small flat with modest hot water use, the 25kW version of the 4000 may be enough. Our guide on how to size a combi boiler explains how installers work it out.
Before you commit to any combi, ask your engineer to measure the mains flow rate, because a 30kW combi can’t produce more hot water than the incoming supply allows.
How Much Does It Cost To Install A Greenstar 4000 30kW In 2026?
A straight combi swap usually costs around £2,200 to £2,900, with relocations and conversions from tank-fed systems costing more.
The boiler is only part of the price. Labour, flue, filter, controls and any pipework changes make up the rest, and the type of job matters most.
| Type of job | Typical installed price (guide only) |
| Combi to combi swap, same location | £2,200 to £2,900 |
| Combi swap with relocation or new flue | £2,700 to £3,500 |
| System or regular boiler to combi conversion | £3,100 to £4,300 |
These ranges include VAT, a magnetic filter, a system flush and standard controls. Treat them as a starting point, since prices vary with access, the flue route, the condition of your existing system and the controls you choose.
Our guide to how much a new boiler costs breaks this down further, and you can spread payments with boiler finance.
What Are The Best Alternatives To The Greenstar 4000 30kW?
The Greenstar 2000 is the cheaper Worcester option, the 8000+ is the step up, and the Vaillant ecoTEC Pro 30 is the closest rival from another brand.
- Worcester Bosch Greenstar 2000 30kW. A simpler, cheaper Worcester combi with a 20kW heating output and 10.8 l/min at a 40°C rise. It’s a good pick for smaller homes on a tighter budget. Read our Greenstar 2000 review.
- Worcester Bosch Greenstar 28CDi or 32CDi Compact. Slightly smaller casings at 280mm deep, which helps where cupboard space is very tight. See our 28CDi Compact review.
- Worcester Bosch Greenstar 8000+ 32kW. Worcester’s premium combi, with a touchscreen display and a 29.6kW heating output. It’s better for larger homes.
- Vaillant ecoTEC Pro 30. A close rival in the same size bracket. See our Vaillant ecoTEC Pro 30 review.
Is The Worcester Bosch Greenstar 4000 30kW Worth It?
Yes, for a one-bathroom home it’s one of the safest choices you can make.
It’s well built, easy to live with and well understood by engineers. For most households, the stronger hot water flow over the 25kW model is worth the small price difference.
Choose it if
- You have one bathroom and up to around 12 radiators
- You’re replacing an older Worcester such as a Greenstar 30i
- You want a reliable mid-range combi with good controls
Look elsewhere if
- You have two bathrooms in regular use at the same time
- Your home is large or has high heat loss and needs more than 24kW for heating
- Price matters more to you than brand, in which case a Greenstar 2000 or another make may suit
Get A Free Boiler Quote From Clever Energy Boilers
Clever Energy Boilers installs Worcester Bosch boilers for homeowners and landlords across the North West, Yorkshire and the Midlands.
We’re Worcester Bosch accredited installers, and our engineers will check your radiators, hot water use and mains supply before recommending the 25kW or 30kW model.
Choose one of our Worcester Bosch boiler installations and you can also take advantage of the long, market-leading warranties available through Clever Energy.
For a fixed price, use our online boiler quote tool. It takes a few minutes, and there’s no obligation.
Frequently Asked Questions
Is The Worcester Bosch Greenstar 30i Discontinued?
Yes, the Greenstar 30i has been discontinued. The Greenstar 4000 30kW is its direct replacement and is still on sale in 2026.
What’s The Difference Between The Greenstar 4000 And The Greenstar 30i?
The 4000 adds a full colour display, the Quick Tap water-saving mode, longer flue options and a larger condensate siphon. Its fixing points also line up with many older Worcester boilers, so swaps are usually straightforward.
How Long Does A Greenstar 4000 Last?
Many run for 10 years or more with a good install and a yearly service. By around 8 years old, though, efficiency has usually dropped and faults become more common, so replacing it is often better value than paying for repairs. A servicing plan such as Clever Care keeps it running safely and efficiently until then.
Is The Greenstar 4000 30kW Suitable For A Flat?
Yes, it’s a good fit for most flats. Its compact size and long flue options make it easier to position, though your installer will still need to check the flue and condensate routes.
Is There An LPG Version Of The Greenstar 4000?
Yes, Worcester makes LPG versions of the Greenstar 4000 for off-gas properties. Our LPG and oil boilers page has more detail.