Worcester Greenstar Boiler Review: 4000 vs 8000+ Compared

What is a Worcester Greenstar boiler?

Greenstar is the name Worcester Bosch gives to its gas condensing boilers, and every current model carries it followed by a number. The number marks the tier: the 4000 is the mainstream mid-range model and the 8000+ is the premium range that replaced the 8000 Life and Style in late 2024.

Worcester Bosch is the UK heating brand of the German Bosch group, building boilers in Worcester. The brand as a whole, including the budget Greenstar 1000 and 2000, is covered in our full Worcester Bosch review; this page is the head-to-head between the two models most installers quote. For how Greenstar compares with other manufacturers' best sellers, see the best combi boilers in the UK.

Two terms used throughout:

• Output (kW) on a combi refers to its maximum hot water power. The heating output to the radiators is often lower.
• Flow rate is how many litres of hot water a minute the boiler can deliver at a stated temperature rise above the incoming mains. All figures below are at a 40°C rise unless marked, so they compare like with like.

How do the Greenstar 4000 and 8000+ compare?

The 4000 is smaller, lighter and cheaper with modest hot water output; the 8000+ is bigger, delivers up to about half as much hot water again as the 30 kW 4000 and carries a longer guarantee. The figures come from Worcester Bosch's professional product pages.

Fitted prices are typical 2026 ranges for a like-for-like combi swap and depend on the output, flue, controls and region. Boiler-only, the 4000 combi typically sells for roughly £1,100-£1,500 and the 8000+ for roughly £1,400-£2,100. Our guide to boiler prices by brand sets these against rivals.

What does the Greenstar 4000 offer?

The 4000 is a compact, well-specified combi for flats and one-bathroom homes, and the logical replacement for an older Greenstar i. Worcester Bosch describes it as built on the design of the Greenstar i, the 24i, 25i and 30i combis that were among the UK's most common boilers.

Documented features from the manufacturer's data:

• Compact casing. At 724 x 400 x 310 mm it is 56 mm shorter, 40 mm narrower and 55 mm shallower than an 8000+, which helps in a kitchen cupboard.
• Wide modulation. The heating output turns down to 3 kW (a 1:10 ratio), so the boiler can tick over gently in mild weather instead of switching on and off.
• Full flow from 1 bar. Worcester quotes full hot water flow from 1.0 bar mains pressure.
• Quiet running. Worcester lists 45 dB(A).
• Controls. Compatible with Bosch EasyControl and with Worcester's optional Intelligent Filling System accessory.
• System version. The Greenstar 4000 system boiler comes in 12, 15, 18, 21 and 24 kW in the same casing, for homes with a hot water cylinder.

The limit is hot water. At 9-10.8 litres a minute, one good shower is fine, but running a second hot tap at the same time weakens both noticeably.

What does the Greenstar 8000+ offer?

The 8000+ is Worcester's premium wall-hung range, built for higher hot water demand and the longest guarantee the brand offers. Worcester launched it in September 2024 as the successor to the Greenstar 8000 Life and Style, raising the most popular combi outputs from 30 and 35 kW to 32 and 36 kW.

Documented features:

• More hot water. 12 litres a minute from the 32 kW model up to 16 litres a minute from the 45 and 50 kW models at a 40°C rise.
• Three layouts. Combi (32-50 kW), system (30 and 35 kW) and regular heat-only versions, in natural gas and LPG.
• Style finish. The 8000+ Style combi in 32 and 36 kW has a gloss black steel front for a kitchen on show.
• Easier swaps. A pre-plumbing jig is designed to line up with the pipework of a CDi Classic or an original 8000, so like-for-like replacements need less re-piping.
• Filling. Combis have a factory-fitted keyless filling link, and an intelligent filling system that tops up pressure automatically is available.

The trade-offs are size, weight and price. The casing is bigger than the 4000, so check the cupboard before you commit, and the extra cost only pays back if you use the extra hot water.

How do the guarantees differ?

The 4000 runs from 7 to up to 10 years and the 8000+ from 8 to up to 12 years, with the longer terms depending on a Greenstar System Filter, registration and, in most cases, a Worcester Accredited Installer.

Worcester's pages state that extended guarantees are not available with the System Filter Micro and that the boiler must be serviced annually. The fee for non-accredited installers has varied between pages, so treat the table as a guide and get the exact term in writing. Our comparison of UK boiler brands shows how these terms stack up against Vaillant, Ideal and Baxi.

What are the documented strengths and weaknesses?

Both models share the brand's main strengths, a large installer and spares network and long conditional guarantees, while differing mostly in hot water output and size.

The heating cap is worth understanding: on the 8000+, the bigger numbers buy hot water, not more radiator heat. A 40 kW and a 50 kW model give essentially the same heating output (33.7 and 33.8 kW), so choose between them on showers and baths alone.

Which Greenstar suits your home?

Choose on hot water demand first, then space and budget. Pick the first line that fits.

Two checks before you decide. First, measure your mains flow: a combi can only heat the water your supply delivers, so a 50 kW model on a 12-litre supply is wasted money. Second, size the heating properly rather than copying the old boiler; our boiler size guide explains how.

What about older Greenstar models?

Older Greenstar boilers remain common and are generally well supported for spares. You will often find:

• Greenstar i (24i Junior, 28i Junior, 25i, 30i): compact combis, now succeeded by the 4000.
• Greenstar CDi Classic: larger combis whose pipework the 8000+ jig is designed to match.
• Greenstar 8000 Life and Style: the 2019 premium range, succeeded by the 8000+.
• Greenstar Ri: Worcester's regular (heat-only) boiler for open-vented systems.

A working older Greenstar does not need replacing just because the range has ended. If it is over 12-15 years old and breaking down repeatedly, our guide to repairing or replacing a boiler helps you weigh it up. Lost the paperwork? Where to find boiler manuals explains how to download the user guide for your model.

What are the common faults and service needs?

Both ranges show a fault code with a short description on the display, and the user guide explains which codes you can safely act on, such as low pressure. Recurring codes involving ignition, overheating or the fan need a Gas Safe registered engineer. Our guide to Worcester Bosch fault codes explains the common ones.

To keep the guarantee valid, both models need an annual service by a Gas Safe registered engineer and the system filter cleaned at each visit. Keep the Benchmark checklist and service records together; Worcester can ask for them when you claim.

Greenstar 4000 or 8000+: which should you choose?

Choose the 4000 if you have one bathroom and want the best value from the brand; choose the 8000+ only if you will use its extra hot water or want the longest guarantee.

• Pick the 4000 for a flat or one-bathroom house, a tight cupboard, or a budget around £2,300-£3,300 fitted.
• Pick the 8000+ for a bathroom plus en suite, strong mains flow, or a 12-year guarantee through an accredited installer, at around £2,800-£4,500+.
• Pick a Greenstar system boiler if two showers run at once; no combi solves that reliably.

If you are also weighing other brands, our Vaillant boilers review covers the closest rival range in the same depth.

Frequently asked questions

What is the difference between the Greenstar 4000 and 8000?

The Greenstar 4000 is a compact mid-range combi in 25 and 30 kW with up to about 10.8 litres a minute of hot water at a 40°C rise. The Greenstar 8000+ is the premium range, from 32 to 50 kW, delivering 12-16 litres a minute, with a larger casing, a touch display and longer guarantees of up to 12 years. The 4000 suits one bathroom; the 8000+ suits busier homes.

How long is the guarantee on a Worcester Greenstar 4000?

Worcester Bosch lists 7 years as standard for the Greenstar 4000 combi, 8 years when a Greenstar System Filter is fitted, and up to 10 years with the filter through a Worcester Accredited Installer, or for a fee through some other registered installers. The boiler must be registered and serviced every year. Terms change, so ask your installer to confirm the length in writing before you sign.

Is the Greenstar 8000 worth the extra money?

It is if you need the hot water. The 8000+ gives 12-16 litres a minute at a 40°C rise against 9-10.8 for the 4000, so it copes better with a bathroom and en suite, and it carries up to 12 years of guarantee. For a home with one bathroom and good mains flow, the 4000 does the same job for typically several hundred pounds less fitted.

What replaced the Worcester Greenstar 30i?

The Greenstar 4000 is the successor to the Greenstar i range, which included the 25i and 30i. Worcester Bosch describes the 4000 as built on the same design as the Greenstar i, and the 30 kW 4000 is the natural replacement for a 30i. Older Greenstar i boilers remain supported for spares, so a working one does not need replacing just because the range has ended.

What is a Greenstar Ri boiler?

The Greenstar Ri is a Worcester Bosch regular, or heat-only, boiler. It heats radiators and a hot water cylinder and relies on cold water and feed-and-expansion tanks in the loft, so it is a like-for-like replacement for older open-vented systems. If you want to keep your tanks and cylinder, a regular boiler such as the Ri or a regular 8000+ model avoids the cost of converting to a combi.

Is the Greenstar 4000 or 8000 better for a three-bed house?

For a three-bedroom house with one bathroom, a 30 kW Greenstar 4000 is usually enough: it gives up to 24 kW of heating and about 10.8 litres a minute of hot water at a 40°C rise. Choose a 32 or 36 kW 8000+ instead if you have a bathroom plus an en suite in regular use, or if your mains flow rate is high and you want stronger showers.

Sources and further reading

• Worcester Bosch Professional - Greenstar 4000 combi
• Worcester Bosch Professional - Greenstar 4000 system
• Worcester Bosch Professional - Greenstar 8000+ combi
• Worcester Bosch Professional - Greenstar 8000+ system
• Worcester Bosch - Launch of the Greenstar 8000+
• Gas Safe Register - Find a registered engineer

Prices and scheme details were checked on 22 October 2026 and are shown as typical ranges. Always get written quotes from Gas Safe registered installers.