Worcester Bosch Greenstar 4000 Review: A Sensible Mid-Range Combi

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The Worcester Bosch Greenstar 4000 is one of the most-fitted combi boilers in the UK, and the model that quietly replaced the Greenstar i in 2022. It’s the boiler your installer will most likely suggest if you ask for “a Worcester for around two and a half grand.” It is also one of the small handful of models you can buy and have installed without ever speaking to a tradesperson, with a fixed price quoted online in around two minutes from either Heatable or BOXT, and finance available from roughly £34 a month.

This review covers what the 4000 is good at, where it falls short of the pricier 8000 series, what you’ll actually pay for it (cash and monthly), and the easiest way to buy it.

Worcester Greenstar 4000 specs at a glance

Type	Gas combi (also available as system / regular)
Output options	25kW or 30kW
Hot water flow rate	10.2 L/min (25kW) · 12.3 L/min (30kW)
Modulation ratio	7:1
ErP efficiency rating	A (heating) · A (hot water)
Dimensions (H × W × D)	690 × 390 × 280mm
Weight	33kg
Warranty	10 years (when installed by a Worcester Accredited Installer and registered)
Made in	Worcester, Worcestershire (UK-built)
From Heatable	From ~£34/month · fixed-price install
From BOXT	From ~£33/month · next-day install available

Both Heatable and BOXT include the boiler, full installation, flue, system flush, controls, and the warranty registration in a single fixed price. Indicative monthly figures are based on a 30kW install at typical 10-year finance terms; your exact figure depends on deposit, term, and home location.

Who the Greenstar 4000 is for (and who should look elsewhere)

The 4000 is the right boiler if you:

• Live in a 1–4 bedroom home with one or two bathrooms
• Want the most-installed boiler brand in the UK so any Gas Safe engineer can service it
• Are replacing an older Worcester (the install is straightforward, often same-day)
• Care more about long-term parts availability and warranty cover than headline efficiency figures
• Want a fixed-price online quote rather than three local engineer surveys

Look elsewhere if you:

• Have a 4+ bathroom home that needs higher hot water flow than 12.3 L/min — consider the Worcester 8000 Style or a Vaillant ecoTEC Plus 38
• Want the absolute best modulation ratio for low-and-slow heating efficiency — the Vaillant ecoTEC Plus modulates 12:1 vs the 4000’s 7:1
• Want a smart-controls-first boiler with native app integration as standard — the Worcester 8000 Lifestyle and Vaillant ecoTEC Plus do this better
• Are on LPG only — the 4000 has fewer LPG variants than older Worcester models

Heating performance

The 4000 is a sensible, mid-range performer. The 7:1 modulation ratio means it can throttle down to roughly 14% of its peak output, which is enough for a typical UK semi but not class-leading. Vaillant’s ecoTEC Plus modulates down to 8% (a 12:1 ratio), which translates to slightly better efficiency on warm shoulder-season days when the boiler is barely working. In practice, the difference shows up as maybe 2–3% on your annual gas bill — real but small.

The 4000 holds an A rating for both heating and hot water under the ErP scheme, the same rating every modern condensing boiler in this class achieves. None of the 25kW or 30kW combis you can legally buy in 2026 are dramatically more or less efficient than each other on paper. Where the 4000 stands out is consistency: it tends not to short-cycle on small heating loads as some cheaper boilers do, partly because Worcester pairs the 4000 with the Comfort+ load-compensation control as a recommended add-on.

If your installer hasn’t suggested the Comfort+ stat or its smarter sibling the EasyControl, ask. A modulating control unlocks load compensation on the 4000, which is the cheapest way to reduce your gas bill on a new boiler install.

What about the Worcester 4000 system boiler?

The Greenstar 4000 also comes as a system boiler in 12kW, 15kW, 18kW, 24kW, and 30kW outputs, designed for homes with a hot water cylinder rather than a combi setup. The 18kW and 24kW system variants are the most-fitted, typically going into 4+ bedroom homes where simultaneous hot water demand makes a combi impractical. Pricing for the system version is £100–£200 less than the equivalent combi as a unit, but you’ll need a hot water cylinder which adds £500–£900 to a fresh install. Heatable and BOXT both quote system installs through their online tools — pick “system” rather than “combi” at the start of the quote and the tool walks you through cylinder sizing.

Hot water performance

The 30kW 4000 produces 12.3 litres of hot water a minute at a 35°C rise, which is the standard “is the shower decent” measurement. That’s enough for one strong shower at full flow, two showers at reduced flow if your home’s plumbing supports it, or a shower running while a kitchen tap fills a kettle. It’s not enough for two strong simultaneous showers, which is the brief for a 4-bathroom home.

The 25kW version drops to 10.2 L/min, which is fine for a one-bathroom flat or a small terrace but starts to feel weedy in a 3-bed semi where two adults shower in series. Most 3-bed homes should default to the 30kW; only choose the 25kW if you have a small home and want to save roughly £150 on the install.

Compared with the Greenstar 8000 Style at 32kW (13.0 L/min), the 4000 30kW is only marginally behind for hot water. You’re not paying the 8000 premium for hot water flow alone.

Smart controls and voice assistant compatibility

Worcester’s EasyControl smart thermostat (an optional ~£250 add-on) works with both the 30kW and 25kW Greenstar 4000. EasyControl integrates with Google Assistant for voice control and Amazon Alexa, and ships with a free app for remote scheduling, holiday mode, and energy use tracking. The “Greenstar 4000 30kW with voice control by Google” listing you’ll see on some installer sites is the EasyControl bundle.

The 4000 also supports OpenTherm, the manufacturer-agnostic protocol that lets the boiler modulate properly with third-party smart thermostats — tado°, Honeywell Evohome, and Drayton Wiser all work. Without OpenTherm, third-party thermostats can only switch the boiler on and off, which loses most of the modulation efficiency. With OpenTherm, the thermostat tells the boiler exactly how hot to run, which is what unlocks the 7:1 modulation in real-world conditions.

If you’re planning to add smart heating later, the 4000 is fully ready for it — no firmware updates or add-on modules needed. Both Heatable and BOXT will add EasyControl or a third-party smart thermostat into the quote tool if you want it bundled with the install.

Build quality and reliability

The 4000 is built at Worcester Bosch’s Worcestershire factory, the same site that produces the 8000 series. Worcester boilers consistently top Which? and Trustpilot reliability surveys among UK manufacturers, with Vaillant as the closest competitor. Repair rates after the warranty period are lower than average for the major brands.

Where the 4000 differs from the 8000 series is in component cost. The 4000 uses a plastic-bodied condensate trap (vs metal in the 8000), a slightly less sophisticated heat exchanger geometry, and fewer sensors for self-diagnosis. None of these affect day-to-day reliability significantly, but they do mean the 4000 is a bit more dependent on routine annual servicing to spot scale or sediment build-up before it becomes a fault.

Spare parts availability for the 4000 is excellent. Any UK Gas Safe engineer can source 4000 parts within 24–48 hours, often same-day from their local merchant. This matters more than people think: a cheaper boiler that needs a £40 part can still cost you a week of cold water if the part is on a four-week back-order from Europe.

Warranty

The Greenstar 4000 ships with a 5-year manufacturer warranty as standard, extending to 8 or 10 years when installed by a Worcester Accredited Installer and registered within 30 days of fitting. Both Heatable and BOXT register the warranty automatically on your behalf as part of their fixed-price install.

Worcester’s warranty is parts and labour, not parts only. That distinction matters: if a heat exchanger fails in year six, Worcester sends a Worcester engineer at no cost, including the call-out and labour time. Some competitor warranties cover parts only, leaving you with a £200–£400 labour bill on a “free” repair.

To keep the warranty valid you need an annual service by a Gas Safe registered engineer. The service doesn’t have to be done by a Worcester engineer — any Gas Safe service is acceptable provided it’s documented and stamped in the boiler logbook.

What the Worcester 4000 actually costs

Boiler-only prices (the unit on a pallet, no install) sit at around £1,300–£1,500 for the 25kW and £1,500–£1,750 for the 30kW from major plumbing merchants. These are not the prices you’ll pay if you buy through an installer, who’ll quote a single fitted price.

Fitted prices via Heatable or BOXT typically land in this range:

• Worcester Greenstar 4000 25kW, like-for-like swap: ~£2,000–£2,400 fitted
• Worcester Greenstar 4000 30kW, like-for-like swap: ~£2,200–£2,600 fitted
• Worcester Greenstar 4000 30kW, conversion (e.g. system to combi): ~£2,800–£3,400 fitted

For a typical 30kW like-for-like swap at £2,400 fitted, finance breaks down roughly as follows:

0% over 24 months	~£100/month · pay £2,400 total
11.9% APR over 5 years	~£53/month · pay ~£3,180 total
11.9% APR over 10 years	~£35/month · pay ~£4,200 total

The 0% deal is the cheapest in absolute terms but has the highest monthly figure. The 10-year plan looks attractive on the monthly but you pay £1,800 more in interest across the term. The 5-year plan is usually the sensible middle. Heatable and BOXT both publish your exact figure inside the quote tool, so you can flip between terms before committing.

Worcester 4000 vs the alternatives

vs Worcester Greenstar 8000 Style. The 8000 is the premium tier: better modulation (10:1), full smart controls integration, slightly higher hot water flow, and a more refined cabinet. Roughly £400–£600 more fitted. Worth it if you’re staying in the home long-term and want the headline boiler; the 4000 is the value-conscious choice that does 90% of the same job.

vs Worcester Greenstar 2000. The 2000 is Worcester’s entry-level model, sitting one tier below the 4000. It’s roughly £200–£300 cheaper fitted, with a shorter standard warranty (typically 7 years vs the 4000’s 10) and a simpler control panel without the OpenTherm support. The right choice if budget is tight and you want to stay within the Worcester ecosystem; for most buyers the 4000 is worth the upgrade for the longer warranty alone.

vs Vaillant ecoTEC Plus 832. The closest competitor at this price point. The Vaillant has better modulation (12:1) and a slightly more efficient pump, but a smaller UK service network than Worcester. Pricing is essentially the same. Pick on installer convenience: Worcester if your local engineer is Worcester-trained, Vaillant if you’re going through Heatable (where Vaillant is often cheaper).

vs Ideal Logic Combi 30. Ideal sits a tier below Worcester on build quality and warranty (typical 7-year vs Worcester’s 10), but is roughly £200–£300 cheaper fitted. The right choice if budget is tight and you’re not staying in the property long-term.

vs Baxi 800 Combi. Strong British brand, 10-year warranty, similar spec to the 4000. Slightly less common installer network outside the major online installers. Worth getting a Baxi 800 quote alongside the 4000 from Heatable for direct comparison.

Pros and cons

Frequently asked questions

Is the Worcester Greenstar 4000 a good boiler?

Yes — for most UK homes it’s one of the safest mid-range choices on the market. It’s reliable, well-supported by spare parts, comes with a strong 10-year warranty, and is fitted by every major online installer in the UK. It’s not the most technically advanced boiler, but it’s the one that most engineers would happily install in their own home.

How much does a Worcester 4000 cost installed?

For a typical 30kW like-for-like swap, expect £2,200–£2,600 fitted from Heatable or BOXT. Conversions (system to combi, or back-boiler to combi) are typically £2,800–£3,400. Both installers quote the exact figure for your home in under two minutes online.

What’s the difference between the Greenstar 4000 and the 8000?

The 8000 is Worcester’s premium tier: better modulation, smart controls integration as standard, higher hot water flow on the larger outputs, and a more refined cabinet. The 4000 covers around 90% of the same use cases for £400–£600 less. The 8000 is the right choice if you’re staying long-term and want the best Worcester makes; the 4000 is the right choice if you want a sensible Worcester at a sensible price.

Is the Worcester 4000 better than the Vaillant ecoTEC Plus?

They’re broadly equivalent in real-world use. The Vaillant has slightly better modulation (12:1 vs 7:1), the Worcester has the larger UK service network. Pricing is similar. Most homeowners choose based on their installer’s preference rather than spec — both are excellent boilers. Heatable often quotes the Vaillant slightly cheaper than the Worcester for the same output.

What’s the warranty on a Worcester 4000?

5 years standard, extending to 10 years when installed by a Worcester Accredited Installer (which includes Heatable and BOXT) and registered within 30 days. The warranty covers parts and labour, not parts only. You need an annual Gas Safe service to keep it valid.

Can I buy a Worcester 4000 online and have it fitted?

Yes. Heatable and BOXT both quote a fixed price online for the boiler plus full installation, including the flue, system flush, controls, and warranty registration. Heatable installs typically happen next day; BOXT often offers next-day installs in major cities. You don’t need to arrange a home survey beforehand.

Does the Worcester 4000 come with smart controls?

No, smart controls are an optional add-on. The standard install includes a basic programmable thermostat. Worcester’s Comfort+ stat is around £180 fitted, the EasyControl smart thermostat (with app and load compensation) is around £250 fitted. Both Heatable and BOXT will add controls inside the quote tool if you want them.

Final verdict

The Worcester Bosch Greenstar 4000 is the boiler we’d recommend to most UK homeowners by default: a sensible, mid-range, UK-built combi from the country’s most-installed brand, with a strong warranty and fittable in a day by either of the two largest online installers. It’s not the most technically advanced boiler, and the modulation ratio specifically lags Vaillant. But for the typical 1–4 bed home, it’s the boiler that gives you the fewest things to worry about across a 10-year ownership.

If you’re buying for a 4-bathroom home or you want best-in-class efficiency, look at the Worcester 8000 Style or Vaillant ecoTEC Plus instead. For everyone else, the 4000 is a quietly excellent choice.

This review was last updated in May 2026. Prices and finance terms quoted are indicative and accurate at time of publishing. Always check the live quote tool for your exact figure before committing. We are not a credit broker, lender or installer — Heatable and BOXT handle quoting, finance and installation directly.