Worcester Greenstar CDi Compact: specifications and warranty

The Worcester Bosch Greenstar CDi Compact is a wall-mounted gas combi boiler sold in the UK, listed by the maker with a central heating efficiency of 94% and an ErP efficiency rating of A¹. It is 280mm deep, which Worcester Bosch describes as compact enough to fit in a standard kitchen cupboard, and it is listed as solar compatible and EasyControl compatible².

The guarantee ladder is the part most households ask about. The CDi Compact carries a 7 year standard guarantee, rising to 8 years with any Greenstar System Filter, and up to 10 years with a filter plus a £40 payment for non-loyalty members¹. The up to 10 year term is also available when the boiler is installed by a Worcester Bosch Accredited Installer or purchased through the company's FastTrack service, with terms and conditions applying².

Worcester Bosch does not publish a list price for the CDi Compact. Prices are installer-quoted, and the only published installed figure in the Greenstar range is for a different model, the Greenstar 2000 30kW with the FastTrack package at £2,475 including VAT and installation³.

Greenstar CDi Compact at a glance: outputs, size and efficiency

The CDi Compact is a combi, so it heats the radiators and produces hot water on demand without a cylinder. Worcester Bosch lists the Greenstar 28CDi Compact with a maximum domestic hot water output of 32.9kW¹. The Greenstar 36CDi Compact LPG is listed with a 36kW central heating output². The maker's own summary of the range is that it suits many homes with up to 36kW hot water output¹.

The physical case is the selling point the name refers to. Worcester Bosch states the boiler is "Compact, Just 280mm deep, fits in a standard kitchen cupboard"¹. That depth matters in flats and kitchens where a standard cupboard run is the only available position, and it is the same figure the maker quotes for the Greenstar i System Compact, so the two share a casing depth¹.

Efficiency is stated at two levels. The product page gives a central heating efficiency of 94% and an ErP efficiency rating of A¹. The directory listing describes the range as "Efficient, A-rated for optimum energy efficiency to help keep bills low"². The ErP label is the regulatory rating; the 94% figure is the maker's central heating efficiency claim. Both are the maker's own published numbers.

For a household, the practical question is whether the output matches the property. A combi sized too large cycles on and off; one sized too small cannot keep up with hot water demand. The range's outputs and the sizing method are set out in boiler sizing, and the wider case for combis over cylinders is in combi boilers.

Specifications: 28, 32 and 36kW models in a 280mm-deep casing

The range is named by nominal output, and the published figures do not always match the model number. Worcester Bosch lists the Greenstar 28CDi Compact with a maximum domestic hot water output of 32.9kW¹. The Greenstar 36CDi Compact LPG is listed with a 36kW central heating output². The maker's range summary describes the line as offering up to 36kW hot water output¹.

The table shows why the model names need reading carefully. The 28CDi Compact is listed with a 32.9kW maximum domestic hot water output, and the LPG variant of the same name is listed with a 10kW central heating output and a 28kW maximum domestic hot water output². Those are the maker's published figures for two separately listed products, and they are not interchangeable.

Worcester Bosch also lists the CDi Compact as compatible with the Greenstar Xtra FGHRS, a flue gas heat recovery unit, and the Xtra unit is listed as compatible with the CDi Compact combi⁴. That is a specification point rather than a standard fitting, and it is worth confirming against the exact model being quoted.

Efficiency: up to 94% and an ErP A rating

Worcester Bosch publishes a central heating efficiency of 94% for the CDi Compact and an ErP efficiency rating of A¹. The directory listing repeats the A rating in plain terms: "Efficient, A-rated for optimum energy efficiency to help keep bills low"². The 94% figure appears elsewhere in the Worcester Bosch range too, including the Greenstar 8000+ Combi, which is also listed at 94% central heating efficiency³.

The ErP rating is the label a household sees on the appliance and in the product fiche. It is a regulatory classification, and A is the top band for a gas boiler of this kind. The 94% figure is the maker's central heating efficiency claim, and it is a steady-state or seasonal figure rather than a guarantee of what a particular installation will achieve.

What determines real-world efficiency is how the boiler is set up and how the system is designed. A condensing boiler recovers heat from the flue gases only when the return water is cool enough, which depends on flow temperature, radiator sizing and system balancing. The controls and settings that shape this are covered in boiler flow temperature and heating system design and balancing, and the rating system itself is explained in boiler efficiency and ErP ratings.

The documents in this range disagree on one point. One product page gives the CDi Compact an ErP efficiency of 92%, while the CDi Compact page used here states 94% central heating efficiency and an ErP rating of A¹. The two figures are not reconciled in the published material, and the 94% figure is the one carried on the current product page.

Guarantee: 7 years as standard, up to 10 with a system filter

The CDi Compact guarantee is a ladder rather than a single number. Worcester Bosch lists a 7 year standard guarantee, 8 years with any Greenstar System Filter, and up to 10 years with any Greenstar System Filter plus a £40 payment for non-WAI loyalty members¹. The same structure appears across the Greenstar range: the Greenstar 4000 is listed at 7 years standard and 8 years with a filter, and the Greenstar 2000 at 5 years standard or 6 with a filter³.

The up to 10 year term has a second route. Worcester Bosch states the CDi Compact carries "Up to a 10 year guarantee when installed by a Worcester Bosch Accredited Installer or purchased via FastTrack", with terms and conditions applying². The company's guarantee matrix, dated December 2025, states that gas boilers carry up to a 12 year guarantee when installed with a Greenstar System Filter, which is a range-wide figure rather than a CDi Compact figure⁶.

The filter itself carries its own terms. Worcester Bosch's guarantee matrix states that Greenstar System Filters carry a 2 year guarantee if they are not installed at the same time as the main heating and cooling appliances⁶. That is a condition worth knowing before assuming the filter is covered for the life of the boiler.

What the guarantee covers and how to qualify for the longer terms

The guarantee is a maker's commitment tied to installation conditions, not an automatic entitlement. Worcester Bosch states that the up to 10 year guarantee applies when the boiler is installed by a Worcester Bosch Accredited Installer or purchased via the FastTrack service, and that terms and conditions apply². The 8 year and 10 year filter terms are stated on the product page alongside the standard 7 year term¹.

The £40 payment is the mechanism for householders whose installer is not part of the loyalty scheme. Worcester Bosch states that non-WAI customers can achieve the extended guarantee length with an additional payment of £40, and that the extended term is available to loyalty scheme members only¹. The same wording appears on other Greenstar models, including the Greenstar Ri and the Greenstar 8000+ Combi⁵.

Claims run through the guarantee certificate. Independent guidance on the Consumer Code for installations states that details on how to submit a claim under the guarantee are contained within the guarantee certificate⁷. For work carried out under a competent person scheme, the installer must provide a written guarantee covering the installation work and an insurance backed guarantee covering that guarantee if the installer stops trading⁸.

That distinction matters for independence. The manufacturer's guarantee covers the appliance; the installer's guarantee and any insurance backed guarantee cover the workmanship. A household relying on a long appliance guarantee still depends on the maker's continued trading and on the installation having been registered correctly. The registration process and the paperwork involved are set out in boiler warranties.

Features: hot water pre-heat, smart controls and solar thermal support

The CDi Compact's headline comfort feature is hot water pre-heat. Worcester Bosch lists a "Hot water pre-heat function available on combi" models, described as instant comfort². Pre-heat keeps a small volume of water warm in the boiler so that hot water arrives at the tap faster, at the cost of some gas used outside the heating season.

On controls, the CDi Compact is listed as EasyControl compatible². Worcester Bosch states that the CDi Compact and the i System Compact "are compatible with a series of room thermostat and programmers from our Comfort range"¹⁰. The Greenstar Comfort I control carries a pre-set heating and hot water programme¹¹. The wider controls picture, including thermostatic radiator valves and zoning, is covered in heating controls and thermostats.

Solar compatibility is listed for the CDi Compact and for the LPG variant². That means the boiler can be paired with a solar thermal system for water heating, with the boiler providing back-up. The technology and its limits are explained in solar thermal water heating.

The CDi Compact is also listed as compatible with the Greenstar Xtra FGHRS flue gas heat recovery unit⁴. Flue gas heat recovery captures heat from the flue that would otherwise be lost, and it is a separate appliance rather than a boiler feature. Flue options and siting are covered in boiler flues.

Installation requirements: condensate pipework and fuel options

The CDi Compact is a condensing combi, so it produces condensate that must be drained. Worcester Bosch lists "Siphonic condensate disposal" as a convenience feature on the CDi Compact¹. Siphonic disposal holds a volume of condensate and releases it in batches rather than a continuous trickle, which reduces the risk of the pipe freezing in cold weather.

Condensate routing is one of the practical constraints on where a combi can go. The pipe must run to a suitable drain with a fall, and where that is not possible internally it may need to run externally with a larger diameter and frost protection. The rules and clearances are set out in boiler installation and boiler flues.

Fuel is the other constraint. Worcester Bosch lists the Greenstar 28CDi Compact with a fuel type of gas (NG) and a separate Greenstar 28CDi Compact LPG with a fuel type of gas (LPG)². Households off the gas grid need the LPG variant, and the two are listed as separate products with different published outputs. The wider picture for properties without a mains gas connection is in LPG boilers and LPG heating and heating a home off the gas grid.

Installation itself is not a household task. Gas work in the UK is restricted to registered engineers, and the competent person scheme arrangements that cover notification and guarantees are described by Certass⁸. For oil and solid fuel work the equivalent registers are OFTEC and HETAS¹². Where a property is on a gas network, connection enquiries go through the network operator's connect service¹⁴.

What the CDi Compact costs in the UK

Worcester Bosch does not publish a list price for the CDi Compact. Prices are installer-quoted, and the company's own route to a price is a home visit: its product pages direct householders to find and contact a Worcester Accredited Installer in their area to book a home visit and get a free quote¹¹.

The only published installed price in the Greenstar range is for a different model. Worcester Bosch lists the Greenstar 2000 30kW with the included FastTrack package at £2,475 including VAT and installation, or £24.94 per month at 10.9% APR including VAT and installation³. That is a Greenstar 2000 figure, not a CDi Compact figure, and it should not be read across to the CDi Compact.

The documents also disagree on CDi Compact pricing. Two separate guidance figures of £1,111 and £942 appear in the published material, and they are not reconciled. Neither is a current installed price, and neither is a Worcester Bosch list price.

What moves a CDi Compact quote is the same set of factors that move any combi quote: the output and model chosen, whether the system type is changing, and flue or condensate routing work. The general cost landscape, including what a like-for-like swap typically involves, is set out in new boiler cost. Running costs by fuel are covered in home heating running costs by fuel.

Worcester Bosch: the company behind the boiler

Worcester Bosch is the UK trading name of the Bosch heating business, and it manufactures and supports a wide range of gas boilers under the Greenstar name. The CDi Compact sits within a range that also includes the Greenstar 2000, 4000 and 8000+ families, and the company lists the Greenstar 2000 as its quietest combi boiler³.

The company's published activity extends beyond gas boilers. Worcester Bosch states that Bosch has over 15 years of expertise in heat pumps, and it operates an Electrified Solutions Team located up and down the country, alongside marketing, technical and design teams supporting installers¹⁶. It also developed a fully functional prototype domestic boiler running on 100% hydrogen at its Worcester research and development site, as a development partner in the BEIS-funded Hy4Heat programme¹⁶.

There is a caution in the company's recent history that bears on any household buying a Worcester Bosch cylinder or a system that depends on one. Worcester Bosch reported that its current cylinder supplier, Range Cylinders, had gone into liquidation, and stated that it would cease sales of its entire domestic cylinder range, including pre-plumbed cylinders for heat pumps, with immediate effect. That decision was reported in August 2025.

For a CDi Compact buyer the position is straightforward. The boiler is a combi, so it does not depend on a Worcester Bosch cylinder. What it does depend on is the gas grid, a gas supplier, and a mains electricity supply for ignition, controls and pumping. The guarantee depends on installation by an accredited installer or a FastTrack purchase, and on a Greenstar System Filter being fitted for the longer terms. Alternatives that change the fuel rather than the boiler are covered in heat pumps compared with boilers and hydrogen-ready boilers.