The Worcester Bosch Greenstar 28CDi Compact is a 28kW gas combi for flats and smaller homes with one bathroom. It’s only 280mm deep, so it’ll fit inside a standard kitchen wall cupboard, and it gives up to 10 litres of hot water a minute at a 40°C rise.
It’s still listed by Worcester Bosch and stocked by UK merchants in 2026, in natural gas and LPG versions. The newer Greenstar 4000 and Greenstar 8000+ ranges sit alongside it. Below, we cover what the 28CDi does well, where it falls short, what it costs to fit and which current models to compare.
What Are The Worcester Bosch 28CDi Compact’s Key Specs?
It’s a 28kW wall-hung gas combi with 24kW for heating, 10 l/min of hot water and an A rating for both heating and hot water.
| Specification | Greenstar 28CDi Compact |
| Boiler type | Wall-hung gas condensing combi |
| Hot water output | 28kW |
| Central heating output | 24kW |
| Hot water flow rate | 10 l/min at 40°C rise (about 11.4 l/min at 35°C rise) |
| ErP rating | A for heating, A for hot water |
| Dimensions (H x W x D) | 690 x 390 x 280mm |
| Fuel | Natural gas or LPG (separate LPG model) |
| Controls | Compatible with Bosch EasyControl and most smart thermostats |
| Status | Still on sale in 2026; newer alternatives are the Greenstar 4000 and Greenstar 8000+ |
What Is The Worcester Bosch Greenstar 28CDi Compact?
It’s the smallest model in Worcester’s Greenstar CDi Compact range, built to give decent hot water from a casing that fits in a kitchen cupboard.
The range comes in three sizes, the 28CDi, 32CDi and 36CDi, and all three share the same 690 x 390 x 280mm casing.
The “28” is the hot water output in kilowatts. The heating side tops out at 24kW, which is plenty for most homes with up to around 10 radiators.
That extra power on the hot water side heats mains water as it flows through, so you get hot water on demand without a cylinder or loft tank.
Worcester Bosch makes it in the UK, and Gas Safe engineers see plenty of them, which helps with servicing and parts. If you already own one, it’s a well-supported boiler with plenty of life left in it, as long as it’s looked after properly.
What Features Does The 28CDi Compact Have?
Its main selling point is size: at 280mm deep it fits inside a standard kitchen wall unit, and that’s why most people pick it.
- Hot water pre-heat. This keeps the plate heat exchanger warm so hot water reaches the tap sooner, and you can switch it off to save gas if you’d rather wait a few seconds.
- Simple control panel. The front display is easy to use, with clear dials or buttons for heating and hot water temperature.
- Smart control compatibility. It works with Bosch EasyControl. Paired with an internet-connected Worcester control, it can reach an A+ package rating for heating.
- Solar compatible. It can take pre-heated water from a solar thermal system.
- LPG option. There’s a dedicated LPG version for off-gas homes. Our LPG and oil boilers page covers this if it applies to you.
How Efficient Is The Worcester 28CDi Compact?
It’s ErP A-rated for both heating and hot water, the same headline rating you’ll see on most modern gas condensing boilers.
In real homes, the bigger savings come from how it’s set up, not the badge on the front. Three things make a real difference to your gas bill:
- Lower flow temperatures. A condensing boiler only condenses properly when the water coming back from the radiators is cool enough. Setting the heating flow at around 55 to 60°C, rather than leaving it on maximum, keeps it in condensing mode for longer.
- Good controls. A room thermostat with weather or load compensation, such as EasyControl or a compatible smart thermostat, stops the boiler cycling on and off.
- Clean system water. A chemical flush and a magnetic filter at installation protect the heat exchanger and help it hold its efficiency over the years.
If you’re replacing an old non-condensing boiler, a properly fitted 28CDi will usually use noticeably less gas.
Swapping out a condensing combi that’s over 8 years old is a different story. The gas saving is smaller, but faults usually become more common at that age, so replacing is often better value than paying for repairs.
What Are The Pros And Cons Of The 28CDi Compact?
The big plus is that it fits in a kitchen cupboard, and the main drawback is that it can’t run two showers at once.
Pros
- Small enough for a kitchen cupboard, so you keep your wall space
- Good hot water performance for a one-bathroom home
- Worcester Bosch parts and engineers are easy to find across the UK
- Works with EasyControl and popular smart thermostats
- Comes in an LPG version
- Pre-heat gives you quicker hot water at the tap
Cons
- Costs more than budget brands with similar outputs
- 10 l/min at a 40°C rise isn’t enough for two showers at the same time
- Older design than the Greenstar 4000, with a simpler display
- Low mains water pressure will limit what you get at the tap, as with any combi
What Size Home Does The 28CDi Compact Suit?
It suits flats, terraces and smaller semis with one bathroom and up to around 10 radiators. In practice, that’s usually a one to three bedroom home where only one person showers at a time.
Got a second bathroom, or an en-suite that’s busy during the morning rush? Step up to the Greenstar 32CDi Compact or the 36CDi Compact. They’re the same physical size, so the choice comes down to how much hot water you use and your incoming mains flow. Our guide on how to size a combi boiler goes into more detail.
A bigger combi won’t fix weak water pressure, though.
Before recommending any combi, your engineer should measure the mains flow rate at the kitchen tap. If it’s below the boiler’s rated flow, the boiler can’t give you more hot water than the mains supplies.
How Much Does It Cost To Install A Worcester 28CDi Compact In 2026?
Expect roughly £2,300 to £3,000 for a straight combi swap, and more if the boiler moves or you’re converting from a tank-fed system.
The job affects the price more than the boiler does. Moving it, or converting from a system or regular boiler, adds pipework and labour, and sometimes a new flue route.
| Type of job | Typical installed price (guide only) |
| Combi to combi swap, same location | £2,300 to £3,000 |
| Combi swap with relocation or new flue | £2,800 to £3,600 |
| System or regular boiler to combi conversion | £3,200 to £4,500 |
These are guide ranges including VAT, a magnetic filter, a system flush and basic controls. Your final price will depend on the condition of your existing system, access, flue length and the controls you pick.
For a wider breakdown, see our guide to how much a new boiler costs. If you’d rather spread the cost, our page on boilers on finance covers monthly options.
What Are The Best Alternatives To The 28CDi Compact?
The closest newer Worcester option is the Greenstar 4000, but the Greenstar 2000, the 32CDi Compact and the Vaillant ecoTEC Pro 28 are worth comparing too.
- Worcester Bosch Greenstar 4000 25kW or 30kW. Worcester’s newer mid-range combi has a colour display, a Quick Tap water-saving function and similar compact dimensions. The 30kW model gives about 12.3 l/min at a 35°C rise. Read our Worcester combi 30 review.
- Worcester Bosch Greenstar 2000. A simpler, cheaper Worcester combi in 25kW and 30kW sizes, aimed at smaller homes. See our Greenstar 2000 review.
- Worcester Bosch Greenstar 32CDi Compact. Same casing, more hot water. It’s the one to look at if you’re borderline between one and two bathrooms.
- Vaillant ecoTEC Pro 28. A popular rival in the same output bracket. Our Vaillant ecoTEC Pro 28 review compares the two.
Is The Worcester Bosch 28CDi Compact Worth It?
Yes, for a small home with one bathroom and not much space, it’s a sensible and reliable choice.
It isn’t the newest Worcester combi, but it does the basics well, it fits where plenty of boilers won’t, and engineers know it inside out.
Choose it if
- Your boiler needs to sit inside a kitchen cupboard
- You have one bathroom and up to around 10 radiators
- You want a Worcester Bosch boiler without paying for the top-end models
Look elsewhere if
- Two people regularly shower at the same time
- You want the latest display and features, in which case look at the Greenstar 4000 or 8000+
- Your budget is tight and price matters more to you than the brand
Get A Free Boiler Quote From Clever Energy Boilers
Clever Energy Boilers fits Worcester Bosch boilers for homeowners and landlords across the North West, Yorkshire and the Midlands.
As Worcester Bosch accredited installers, we check your mains flow rate, radiator count and hot water use first, so you don’t pay for more boiler than you need.
Long, market-leading warranties are available through Clever Energy on our Worcester Bosch boiler installations. Every job is finished with a system clean, a magnetic filter and full commissioning.
You can get a fixed price in a few minutes with our online boiler quote tool. There’s no obligation to go ahead.
Frequently Asked Questions
Is The Worcester Bosch 28CDi Compact Discontinued?
No, it’s still listed by Worcester Bosch and sold by UK merchants in 2026, alongside the newer Greenstar 4000 and 8000+ ranges.
How Many Radiators Can A 28CDi Compact Run?
Up to around 10 radiators in most homes. Its 24kW heating output keeps a well-insulated home of that size comfortable, but your engineer should confirm it with a heat loss estimate.
What’s The Difference Between The 28CDi Compact And The 29CDi Classic?
The 29CDi Classic is bigger and discontinued, with a deeper 360mm casing and a slightly higher hot water flow rate. The 28CDi Compact is smaller and still on sale.
Can The 28CDi Compact Be Installed In A Flat?
Yes, its size and flue options make it a good fit for flats. Your installer will check the flue route and condensate pipe run before quoting.
Does The 28CDi Compact Work With Hive Or Nest?
Yes, it works with Hive, Nest and most other smart thermostats, as well as Worcester’s own Bosch EasyControl. Our Hive vs Nest guide compares the two.