Latest Buyers Guide for Worcester Bosch Greenstar Ri An Ultimate Boiler
Worcester Bosch Greenstar Ri Regular Boilers; part of the PlumbNation Worcester Greenstar boiler collection, is a market-leading range of energy-saving condensing gas-fired boilers. With average prices excluding VAT and installation starting from £540, the RI range makes an ideal choice for those looking to replace an ageing heat-only boiler.
The Greenstar Ri range is available in four heating outputs, which means there’s a model to suit most property types. Key features include a SEDBUK A rating for optimum energy saving, and a NOx Class 5 rating for the lowest carbon emissions.
It is also the smallest Worcester boiler; with compact dimensions that enable it to fit easily into a kitchen cupboard. The Greenstar RI should be used in an open-vent heating system that uses a hot water storage cylinder, plus it is fully compatible with the Greenskies Solar Panels.
For peace of mind, it has an extended warranty and is made from robust, cast iron and aluminium to increase its lifespan.
You can expect to pay anything between £769.83 and £998.40 for the Worcester Bosch Greenstar Ri Regular Boiler, which includes VAT and excludes the cost of installation.
Available in six heating outputs including 12kW, 15kW, 18kW, 24kW, 27kW and 30kW, the Greenstar Ri Regular is an energy-saving heat only condensing boiler that is suitable for homes with a traditional heating and hot water system.
This means you need a separate cold-water tank and hot water cylinder. Measuring in at 600mm (H) x 390mm (W) x 270mm (D), it is one of the smallest boilers in the Worcester Bosch range and can even fit in a standard kitchen cupboard.
This boiler comes with a 5-year manufacturer warranty, and the range includes options for small, medium and large homes. Prices start at £769.83 and go up to £998.40, and the amount you will need to spend will depend on which output level you require. We can help you with our seven best findings available:
Worcester Bosch Greenstar 12Ri Regular Gas Boiler | 9.2/10 | YES | £814 | 92% |
Worcester Bosch Greenstar 15Ri Regular Gas Boiler | 9.2/10 | YES | £843 | 92% |
Worcester Bosch Greenstar 18Ri Regular Gas Boiler | 9.2/10 | YES | £898 | 92% |
Worcester Bosch Greenstar 21Ri Regular Gas Boiler | 9.2/10 | YES | £996 | 92% |
Worcester Bosch Greenstar 24Ri Regular Gas Boiler | 9.2/10 | YES | £954 | 92% |
Worcester Bosch Greenstar 27Ri Regular Gas Boiler | 9.2/10 | YES | £1114 | 92% |
Worcester Bosch Greenstar 30Ri Regular Gas Boiler | 9.3/10 | YES | £1080 | 93% |
Worcester Bosch Greenstar 12Ri Regular Gas Boiler
The Worcester-Bosch Greenstar 12Ri is a regular condensing boiler that is sufficiently compact and lightweight to be mounted on a kitchen wall in combination with a traditional domestic central heating pump and hot water storage cylinder etc.
It is powerful enough to provide high-efficiency central heating and hot water for a small house or flat.
The appliance employs a robust and highly efficient heat exchanger constructed from cast aluminium and silicon which allows the latent heat in exhaust gases to be extracted for useful purposes rather than being lost through the boiler flue.
Indeed the Worcester-Bosch Greenstar 12Ri is rated as highly efficient by SEDBUK 2009 (Seasonal Efficiency of Domestic Boilers in the United Kingdom) and is in band B for energy efficiency.
The Greenstar 12Ri is 92% efficient in terms of fuel consumption in other words nearly 90% of the natural gas or LPG (Liquefied Petroleum Gas) burnt is converted into useful heat and can reduce heating bills by up to 35% in comparison to old non-condensing boilers.
This boiler is recommended by the Energy Saving Trust.
Advantages:
- SEDBUK Band A
- High energy efficiency
- NOx Class 5- Low NOx and CO2 emissions
- Environmentally friendly
Disadvantage:
- A slight lack of compatibility with the smart thermostat.
Features:
Band Rating | A Rated |
ERP Rating | A HEAT |
Central Heating Max. Output | 12kW |
Flow Rate | N/A |
LPG Compatible | Yes |
Mounting | Wall mounted |
Typical Price (inc VAT) | £814 |
Typical installation Cost (inc VAT)* | £500 – £1,000 |
Total Cost | £1,314 – £1,814 |
Product Key Features:
Make | Worcester Bosch |
Model | Greenstar 12Ri Regular Gas Boiler |
Is Condensing | Condensing |
Efficiency Rating | 92% |
Standard Warranty | 5 Years |
Worcester Bosch Greenstar 15Ri Regular Gas Boiler
The Worcester-Bosch Greenstar 15Ri is one of the smallest of the regular also known as conventional or traditional condensing boilers available form Worcester-Bosch.
The appliance is capable of outputting between 3.7kW and 12.3kW to domestic hot water and central heating systems but is no less efficient than some of its more powerful cousins.
Indeed the Worcester-Bosch Greenstar 15Ri is 92% energy efficient in its natural gas guise and 89.8% energy efficient in its LPG (Liquefied Petroleum Gas) variant meaning that it is classified as A rated for energy efficiency by SEDBUK.
This is in comparison to an efficiency of around 75% or less for some other conventional boilers especially older boilers so it is easy to see how the Worcester-Bosch Greenstar 15Ri can reduce your domestic fuel costs and your carbon footprint.
The Worcester-Bosch Greenstar 15Ri is also compact in terms of its dimensions H600mm x W390mm x D270mm and weighs just 22.6kg so can be installed in a kitchen cupboard an airing cupboard or in a different location depending upon your specific requirements.
The appliance is supplied with a wall mounting bracket for attachment to a wall surface and levelling screws which allow the boiler unit to be adjusted so that it lies plumb against the wall.
This boiler is recommended by the Energy Saving Trust.

Advantages:
- Compact dimensions for cupboard fit & wall hung
- Siting flexibility
- Compatible with Greenskies solar panels
- Alternative energy option
Disadvantage:
- A slight lack of compatibility with the smart thermostat.
Features:
Band Rating | A Rated |
ERP Rating | A HEAT |
Central Heating Max. Output | 15kW |
Flow Rate | N/A |
LPG Compatible | Yes |
Mounting | Wall mounted |
Typical Price (inc VAT) | £843 |
Typical installation Cost (inc VAT)* | £500 – £1,000 |
Total Cost | £1,343 – £1,843 |
Product Key Specifications:
Make | Worcester Bosch |
Model | Greenstar 15Ri Regular Gas Boiler |
Is Condensing | Condensing |
Efficiency Rating | 92% |
Standard Warranty | 5 Years |
Worcester Bosch Greenstar 18Ri Regular Gas Boiler
The Worcester Bosch Greenstar 18Ri is a highly reliable condensing regular gas boiler that’s ideal for homes with lower demand for heating and hot water.
The output rating of 18 kW is ideal for homes with 1 bathroom and a low heating and hot water demand but being a regular boiler might not make it an ideal choice for smaller properties.
Regular boilers directly heat the central heating system and also produce hot water for a cylinder. As a hot water cylinder is needed, often fed by a cold-water storage cistern in the attic, regular boilers aren’t suitable for smaller properties.
A seasonal efficiency rating of 92% and ErP A-rating for heat makes the Greenstar 18Ri a highly efficient unit.
As well as this 18 kW model, the Greenstar range also includes boilers with many other outputs: 9 kW, 12 kW, 15 kW, 21 kW and 24 kW. The 9 kW, 12 kW and 15 kW models are all suitable for smaller homes with 1 bathroom that don’t have a high demand for heating and hot water. Meanwhile, the 18 kW, 21 kW and 24 kW units can meet the heating and hot water demands of medium-sized homes.
Greenstar Ri boilers include frost protection, a simple boiler control for maximum control and full compatibility with Worcester Greenskies solar panels.
Thanks to being highly efficient, the Greenstar 18Ri will help to reduce energy bills and being compact and lightweight will keep installation costs to a minimum. It’s also compatible with Worcester Greenskies solar panels for further savings.
As a wall-mounted compact boiler, the 18Ri can be installed within a standard cupboard to save space around the home. Plus, a frost protection feature means it can be installed in a loft or garage too.
Available with a 5-year warranty as standard, that can be extended to 10 years when installed by a Worcester Accredited installer, you’ll be well covered by Worcester Bosch.
Advantages:
- Robust cast aluminium/silicon construction
- Boiler reliability
- Reversible flow and return pipes
- Easy installation
Disadvantage:
- A slight lack of compatibility with the smart thermostat.
Features:
Band Rating | A Rated |
ERP Rating | A HEAT |
Central Heating Max. Output | 18kW |
Flow Rate | N/A |
LPG Compatible | Yes |
Mounting | Wall mounted |
Typical Price (inc VAT) | £898 |
Typical installation Cost (inc VAT)* | £500 – £1,000 |
Total Cost | £1,398 – £1,898 |
Product Key Specifications:
Make | Worcester Bosch |
Model | Greenstar 18Ri Regular Gas Boiler |
Is Condensing | Condensing |
Efficiency Rating | 92% |
Standard Warranty | 5 Years |
Worcester Bosch Greenstar 21Ri Regular Gas Boiler
The Worcester Bosch Greenstar 21Ri is a condensing regular gas boiler with an output rating of 21 kW.
If you’re looking for a heating system that could help to lower your energy bills then the Greenstar 21Ri is a great option thanks to a 92% efficiency rating and ErP A-rating for heat.
The 21kW output rating makes the Greenstar 21Ri ideal for installation in homes with 10-15 radiators and 1-2 bathrooms.
This range of regular boilers are available in a number of different outputs, including 12 kW, 15 kW, 18 kW and 24 kW in addition to this 21 kW model.
A regular boiler should be installed into properties as part of an open vent heating system. This means that in addition to the boiler there will also be a cold water tank in the loft and a hot water cylinder.
A 5-year warranty is available as standard which can be extended to 7 or 10 years when certain terms and conditions are met.
Greenstar Ri boilers feature simple-to-use controls and can be paired with Greenskies solar panels. Plus, if you choose to have the boiler fitted into a garage or loft area, then the frost protection feature will prevent it from freezing during the winter months.
Thanks to compact dimensions of 600 x 390 x 270mm (HxWxD) the Greenstar Ri can be installed into a standard kitchen cupboard.
Advantages:
- Weighs only 22.6 kg.
- Easy Installation
- Worcester- Bosch brand reliability
- Peace of mind
Disadvantage:
- A slight lack of compatibility with the smart thermostat.
Features:
Band Rating | A Rated |
ERP Rating | A Heat |
Central Heating Max. Output | 21 kW |
Flow Rate | N/A |
LPG Compatible | Yes |
Mounting | Wall Mounted |
Typical Price (inc VAT) | £996 |
Typical installation Cost (inc VAT)* | £500 – £1,000 |
Total Cost | £1,496 – £1,996 |
Product Key Specifications:
Make | Worcester Bosch |
Model | Greenstar 21Ri Regular Gas Boiler |
Is Condensing | Condensing |
Efficiency Rating | 92% |
Standard Warranty | 5 Years |
Worcester Bosch Greenstar 24Ri Regular Gas Boiler
The Greenstar 24Ri is a condensing regular gas boiler that has been designed and manufactured by Worcester Bosch.
The Greenstar 24Ri has a 24 kW output rating, making it most suitable for smaller/medium-sized homes that don’t have such a high demand for heating and hot water.
A seasonal efficiency rating of 92% makes the Greenstar 24Ri a highly efficient boiler that also has an ErP A-rating for heat.
Regular boilers (conventional or heat-only too) heat the central heating system directly and produce hot water for a cylinder. Due to needing a hot water cylinder, which is often fed by a cold-water storage cistern located in the attic, regular boilers aren’t suitable for smaller properties where space is limited.
The Worcester Bosch Greenstar Ri range includes several models with varying outputs to help find the ideal unit for most homes. As well as this 24-kW model, there are also 9 kW, 12 kW, 15 kW, 18 kW and 21 kW boilers available.
The 9 kW, 12 kW and 15kW boilers are suitable for smaller homes with 1 bathroom and low demand for heating and hot water. Meanwhile, the 18kW and 21kW boilers can meet slightly higher demands.
Thanks to being highly efficient, the Greenstar 24Ri will help to reduce your energy bills. Plus, its compact size and lightweight will lower the initial costs of installation.
Save even more money by pairing it with Worcester Greenskies solar panels.
As a compact wall-mounted boiler, Worcester Bosch has designed this boiler to fit within a standard kitchen cupboard. The inclusion of a frost protection feature means that it can be installed into a loft or garage too.
The Greenstar 24Ri comes with many features and benefits including simple boiler controls to give maximum control over the unit and the ability to pair it with Worcester Greenskies solar panels.
Available with a 5-year warranty as standard, which can be extended to 10 years when installed by a Worcester Bosch accredited installer, you’ll have peace of mind that you’re getting a highly reliable unit that won’t let you down.
Advantages:
- 10-year guarantee on primary heat exchanger
- Peace of Mind
- COMPACT AND LIGHTWEIGHT
- CAN BE PLACED ALMOST ANYWHERE IN THE HOME
Disadvantage:
- A slight lack of compatibility with the smart thermostat.
Features:
Band Rating | A Rated |
ERP Rating | A HEAT |
Central Heating Max. Output | 24kW |
Flow Rate | N/A |
LPG Compatible | Yes |
Mounting | Wall mounted |
Typical Price (inc VAT) | £954 |
Typical installation Cost (inc VAT)* | £500 – £1,000 |
Total Cost | £1,454 – £1,954 |
Product Key Specifications:
Make | Worcester Bosch |
Model | Greenstar 24Ri Regular Gas Boiler |
Is Condensing | Condensing |
Efficiency Rating | 92% |
Standard Warranty | 5 Years |
Worcester Bosch Greenstar 27Ri Regular Gas Boiler
The Greenstar 27Ri regular gas boiler is a wall-mounted unit by Worcester Bosch. This boiler comes in a range of outputs such as 12kW, 15KW, 18kW, 24kW, 27kW, and 30 kW. The Greenstar RI has an output of 27 kW and an efficiency rating of 92% making it an A-rated boiler.
With this wide range of outputs, this boiler can fit in almost anyone’s home whether it is a medium or a large size. This model is compact meaning that it can be hidden away out of sight, as well as save you room with it being small enough to be installed in a standard-sized kitchen cupboard.
This boiler has simple control knobs as well as user-friendly displays for ease of use. As well as this it is compatible with a wide range of accessories such as the Greenskies solar panels for energy and cost savings.
As well as this it can be used with the Worcester Bosch range of high-efficiency Green store cylinders for a complete Worcester system solution for your home. This boiler comes with a wide choice of controls helping to increase the comfort and economy.
As well as this it comes with 5 Years warranty, which is extendable to 10 years when installed by a Worcester Bosch accredited installer, giving you the added security that you have a reliable boiler.
Advantages:
- A-RATED CONVENTIONAL BOILER
- SAVE MONEY ON YOUR GAS BILL
- COMPATIBLE WITH GREENSKIES SOLAR PANELS
- ALTERNATIVE ENERGY AND COST SAVINGS OPTION
Disadvantage:
- A slight lack of compatibility with the smart thermostat.
Features:
Band Rating | A Rated |
ERP Rating | A Heat |
Central Heating Max. Output | 27kW |
Flow Rate | N/A |
LPG Compatible | Yes |
Mounting | Wall Mounted |
Typical Price (inc VAT) | £1,114 |
Typical installation Cost (inc VAT)* | £500 – £1,000 |
Total Cost | £1,614 – £2,114 |
Product Key Specifications:
Make | Worcester Bosch |
Model | Greenstar 27Ri Regular Gas Boiler |
Is Condensing | Condensing |
Efficiency Rating | 92% |
Standard Warranty | 5 Years |
Worcester Bosch Greenstar 30Ri Regular Gas Boiler
Worcester Bosch has designed and manufactured the Greenstar 30Ri as a condensing regular gas boiler that’s suitable for larger homes.
A seasonal efficiency rating of 93% makes this a highly efficient boiler that also has an ErP A-rating for heat.
An output rating of 30kW makes this Worcester Bosch boiler perfect for larger homes with 2+ bathrooms and a higher demand for heating and hot water.
There’s plenty of choices when looking to install a Worcester Bosch Greenstar boiler. You not only have to install a gas boiler, but LPG is also available. Also, there are multiple output ratings in addition to this 30 kW model, including 12 kW, 15 kW, 18kW 24kW and 27 kW boilers.
Thanks to featuring flexible flues, the Greenstar 30Ri can be installed just about anywhere and being a compact wall-mounted unit means it can be installed within a standard cupboard, out of sight.
This boiler can save you money thanks to its high-efficiency rating allowing you to reduce your energy bills. As well as this it is an easy to install boiler allowing you to save the much-needed money on installation costs as well as saving you time
Regular boilers directly heat the central heating system and also produce domestic hot water for a cylinder. As they need a hot water cylinder, often fed by a cold water storage cistern in the loft, regular boilers aren’t suitable for smaller properties or homes where space is limited.
Features of the Greenstar 30Ri include frost protection to reduce freezing during the cold winter months, simple boiler controls for maximum control and the ability to be paired with Worcester Greenskies solar panels.
Greenstar 30Ri boilers are available with a 5-year warranty as standard with the option to extend this to 10 years when installed by a Worcester Accredited Installer.

Advantages:
- FROST PROTECTION
- REDUCES FROST RISK
- LOW NOX AND CO2 EMISSIONS
- ENVIRONMENTALLY FRIENDLY
- 5-YEAR PARTS AND LABOUR WARRANTY
Disadvantage:
- A slight lack of compatibility with the smart thermostat.
Features:
Band Rating | A Rated |
ERP Rating | A Heat |
Central Heating Max. Output | 30kW |
Flow Rate | N/A |
LPG Compatible | Yes |
Mounting | Wall Mounted |
Typical Price (inc VAT) | £1,080 |
Typical installation Cost (inc VAT)* | £500 – £1,000 |
Total Cost | £1,580 – £2,080 |
Product Key Specifications:
Make | Worcester Bosch |
Model | Greenstar 30Ri Regular Gas Boiler |
Is Condensing | Condensing |
Efficiency Rating | 93% |
Standard Warranty | 5 Years |
BUYING GUIDE- Worcester Bosch Greenstar Ri Boilers
Is the Greenstar Ri Regular the Right Boiler Type and Size for Your Home?
With a total of six outputs in the Greenstar Ri Regular range, there is a solution for most small, medium and large properties. This boiler is a particularly great option if you want to replace an old conventional boiler because you will already have a cold-water storage tank and hot water cylinder – two things this boiler requires in order to provide you with ample heating and hot water.
The Greenstar 12Ri, 15Ri and 18Ri are better suited to smaller homes with a maximum of 8 radiators and 1 bathroom, and the 24Ri is ideal for medium houses with no more than 10 radiators, 1 family bathroom and possibly an ensuite. As for the 27Ri and 30Ri (the two higher outputs), both are perfect for medium and large-sized homes with multiple bathrooms. However, the Greenstar Ri Regular won’t be suitable for all properties, so you must get a Gas Safe engineer to check whether this appliance is a viable option for your home.
Greenstar Ri Regular Technology and Main Advantages
Worcester’s Greenstar Ri Regular features a smart heat exchanger (with a 10-year guarantee) that recycles exhaust gases and re-uses latent heat to maximize energy-saving performance. The boiler also has a fascia-mounted heating temperature control knob, as well as a neon operational status indicator so that the boiler does not waste energy by exceeding your heating requirements.
Frost protection is included to eliminate the risk of cold weather damage, which is ideal if you plan to install the appliance in your loft, basement or garage. The Greenstar Ri Regular has a user-friendly control panel and displays too, making it easy for you to adjust heating temperatures day and night.
By being compact, the boiler can be kept almost anywhere in your home, and the multi-directional flue options help with siting flexibility as well. It also comes with a wall-mounting kit to enable your engineer to install the appliance efficiently and make sure the pipes are neatly hidden behind the unit. And if you like the idea of having a complete Worcester system, you can opt for a high-efficiency Green store cylinder.
Boiler Energy Efficiency Credentials
The Greenstar Ri Regular has a SEDBUK A rating for optimum energy efficiency and can reduce your heating bills by up to 20%. It’s also an Energy Saving Trust endorsed appliance and up to 30% cheaper to run than older conventional boilers. Although 91% efficient as it comes, the boiler can be used with Greenskies solar panels for further energy and cost savings. Furthermore, this condensing gas-fired appliance has a NOx Class 5 rating for the lowest carbon emissions.
What we think of the Worcester Greenstar Ri
The Greenstar RI boiler has a fascia-mounted heating temperature control knob and neon operational status indicators for fuel consumption, to stop it from exceeding your household’s heating requirements. For easy installation, it also is equipped with multi-directional flying above or below it.
A workmanlike range of boilers which have been designed to replace the more traditional heating systems in older properties. In other words, these are not Combi units and do not provide hot water for the taps on demand. Instead, they are heat-only boilers and that means they send hot water to the radiators and store it in a hot water tank for use by the taps. This requires a cold-water cistern and expansion tank.
There are four models in the range, going from a modest 12kW to a more powerful 24kW.
Although they are powerful units which can cope with a wide range of property sizes, these are not big units, weighing just 22.6kg. And given their compact size, they can be placed in a kitchen cupboard. Controls are a little basic, but enough to be operated efficiently.
Getting a Competitive Boiler Quote
We recommend you do some research before purchasing your new Greenstar RI Regular boiler. Look for a few quotes from local boiler installers and one from a national installer to find the best boiler price.
To ensure the work carried out is safe and of high quality, make sure your engineer is Gas Safe Registered.
What Do Industry Experts Have To Say?
“At Worcester, we recognize the vital role you play in the specification and installation of energy-efficient appliances in homes across the UK. We will continue to invest in our products, people, facilities and added-value services to ensure you have all you require to deliver only the best solutions to your customers’ requirements.”
Carl Arntzen, Managing Director, Bosch Thermotechnology Ltd.
Established in 1962, Worcester Bosch Group has delved into many different avenues over the years. From small engineering works to becoming market leaders in the boiler industry, they have built a good reputation for themselves across Europe. Worcester Bosch Group is leading suppliers of domestic boilers in the UK, their range includes a mixture of combi boilers, system boilers and regular boilers. But what makes Worcester Bosch boilers so popular with homeowners? Our experts discuss the Greenstar I combi boiler, Greenstar I System and Greenstar Ri (12kW to 24kw). The boilers mentioned are Worcester Bosch’s three best selling products, so for any more information just contact a member of our team today!
Greenstar i combi boiler
The Greenstar I combi boiler is ideal for smaller homes that have one bathroom, it has been installed in over 1 million homes across the UK. The latest model includes a simple user-friendly control that easily lets homeowners adjust all heating and hot water requirements at the touch of a button. The Greenstar I combi boiler can also guarantee zero risks of condensate pipe freezing in severe weather, which gives any homeowner or landlord about its high-quality longevity all year round.
Greenstar i System (9kW to 24kW)
Worcester Bosch’s most popular system boiler, the Greenstar I System is suitable for any small to medium-sized home. Its simple boiler controls display clear information that is easy to understand for any homeowner and gives more control. This product can be used with Greenskies solar panels, to ensure your home has a low carbon footprint, whilst also saving you money!
Greenstar Ri (12kW to 24kW)
The Greenstar Ri boiler is recommended for small and medium-sized homes as it’s a compact wall-mounted product. It can even be installed in a standard kitchen cupboard so that it can be hidden in your kitchen if you’re worried it won’t match your home aesthetic. It also has frost protection so there’s less risk of developing frost if installed in a garage or loft area. The Greenstar Ri boiler can be used with any existing hot water storage cylinder, so there’s no need for a replacement!
https://www.greenstarservices.co.uk/news/why-are-worcester-bosch-boilers-so-popular
Construction and Material:
SEALED HEATING SYSTEMS
If the appliance is fitted to a sealed heating system, which is pre-pressurized, your installer will advise you of the minimum and maximum pressure which should be indicated on the pressure gauge. Check regularly that the pressure is maintained and contact your installer or maintenance engineer if a permanent significant drop in pressure is indicated on the pressure gauge. If the system loses pressure it should be repressurized and the cause of the fall investigated.
CENTRAL HEATING SYSTEMS
During the first few hours of operation of the central heating system, check that all radiators are being heated at an even rate. If the top of a radiator is at a lower temperature than the bottom then it should be vented by releasing air through the venting screw at the top of the radiator. Ask your installer to show you how this
is done. If the boiler is fitted to a sealed system, repeated venting will reduce the quantity of water in the system and this must be replenished for safe and satisfactory operation of the appliance. Should water leaks be found in the system or excessive venting is required, then a service engineer must be contacted to inspect the installation and rectify any fault. Only additives that are compatible with aluminium may be used in the system. Any incompatible additive used will invalidate the guarantee.
CONDENSATE DRAIN
This is a condensing appliance and the terminal will, at times give out a plume of water vapour. This is quite normal. The appliance also produces quantities of condensate which is discharged regularly, by a syphon within the boiler, to drain.
CLEARANCES – VENTILATED COMPARTMENT
Your installer will have provided adequate space around the appliance for safety and servicing access. Do not restrict this space with the addition of cupboards, shelves etc. next to the appliance.
ROOM THERMOSTAT
A room temperature controller and programmer should be fitted to control the central heating. Refer to the instructions supplied with the thermostat for information on siting and setting.
THERMOSTATIC RADIATOR VALVES
It is recommended that this type of valve is fitted to all but one of the radiators (or at least those in the sleeping accommodation). The remaining radiator, which must be where the room thermostat is located, should be uncontrolled and must be left open.
BOILER CLEARANCES – UNVENTILATED COMPARTMENT
Space required for unventilated areas with a removable door or panel.
600mm clearance required to a fixed surface for servicing.
This space can be reduced to 50mm for one side only provided that the side clearances add up to the total of both the side measurements shown or more.
VENTILATION
This is a room sealed appliance and does not require any air for combustion from inside the property. If the appliance is fitted into a cupboard or a compartment is built around the appliance after installation, then the compartment must be separated from the boiler space by a perforated non-combustible partition as described in BS 6798. Notwithstanding the requirements of BS 6798 and BS 5440 there is no need for ventilation openings to be provided in the compartment because of the low heat loss from the appliance casing, if the clearances shown are maintained. Do not operate the appliance if the flue terminal fitted on the outside wall or roof is obstructed or damaged.
PUMP ANTI-SEIZURE
If there has been no heating demand for 24 hours the boiler will run the system pump for a few seconds to reduce the possibility of pump seizure during long periods of inactivity, which is usually more frequent during the summer months.
Research & methodologies used behind the in-depth analysis of Worcester Bosch Greenstar Ri Boilers:

- 300mm adjacent to a boundary line.
2. The dimension below eaves, balconies and car ports can be reduced to 25mm, as long as the flue terminal is extended to clear any overhang. External flue joints must be sealed with suitable silicon sealant.
3. 1,500mm between a vertical flue terminal and a window or dormer window.
4. 1,200mm between terminals facing each other.
5. Vertical flue clearance, 300mm adjacent to a boundary line.
6. 600mm distance to a boundary line, unless it will cause a nuisance. BS 5440:Part 1 recommends that care is taken when siting terminal in relation to boundary lines.
7. 600mm minimum clearance from a skylight to a vertical flue.
8. Vertical flue clearance, 500mm to non-combustible building material, and 1,500mm clearance to combustible building material.

9. 300mm above, below and either side of an opening door, air vent or opening window.
10. 600mm diagonally to an opening door, air vent or opening window.
11. 300mm to an internal or external corner.
12. 2,000mm below a Velux window, 600mm above or to either side of the Velux window.
13. 400mm from a pitched roof or 500mm in regions with heavy snowfall.
14. 500mm clearance to any vertical structure on a roof, 600mm to room sealed flue or 1,500 to an open flue.
15. 200mm below eaves and 75mm below gutters, pipe and drains.
16. The dimension below eaves, balconies, and carports can be reduced to 25mm, as long as the flue terminal is extended to clear any overhang. External flue joints must be sealed with suitable silicone sealant.
17. Flue clearance must be at least 300mm from the ground. Terminal guards must be fitted if the flue is less than 2 metres from the ground or if a person could come into contact with the flue terminal.
18. 600mm distance to a surface facing a terminal, unless it will cause a nuisance. BS 5440: Part 1 recommends that care is taken when siting terminals in relation to surfaces facing a terminal.
- • Installations in car ports are not recommended
- • The flue cannot be lower than 1,000mm from the top of a light well due to the build-up of combustion products
- • Dimensions from a flue terminal to a fanned air inlet to be determined by the ventilation equipment manufacturer.
Stories From The Real-World Use Cases

Before resetting your boiler, make sure your system is actually calling for heat. You will need to check:
Controls and thermostats. First, check your boiler thermostat. This will be a dial on the boiler with numbers or possibly a ‘min’ and ‘max’ setting. This should be set fairly high. Next, check your overall room thermostat. There are many designs but most will include a dial and a digital readout. If the dial has been turned down too low (e.g., to below 18 degrees) then your system will only request heat when the temperature of your room drops to below that level – which may not happen often.
Next, check the control panel for your heating and boiler (you may need to retrieve the instructions manual). If the heating and hot water are set to ‘off,’ your boiler will not come on. If it is set to ‘timed,’ it will only come on between the times you set.
Next, check the pressure gauge. In many Worcester Greenstar boilers, this will be behind a flap at the bottom. Check that the pointer is in the green zone and is around 1.5 bar. If it is in the red (low or high) you will need to call a Gas Safe registered engineer.
Please note, iIf you have an older system with a tank in the loft, the pressure is maintained automatically and you probably won’t find a gauge.
Finally, check the gas supply to other appliances in your home (gas fire, cooker, etc.) If these are not working either and your gas supply is set to be on, you should call your gas supplier for advice.
Top Reviews:
- Name: Brian Turnbull
- Date: 20th February 2014 at 2:33 pm
- Feedback in Detail:
A Worcester Greenstar 15Ri boiler was installed in my home by British Gas on the 4th of November 2013.
Now, after 4 months, I have found this boiler & its installation has been well above my original expectations in terms of efficiency, design/appearance & temperature control.
A first review of energy cost savings has now been completed & I have been surprised at the difference between this product & my previous outdated boiler.
Congratulations all round.
- Name: Ian Edwards
- Date: 17th August 2015 at 9:56 pm
- Feedback in Detail:
I have just installed one Greensted 18i best thing I ever did. Would recommend to anyone.
- Name: Colin Paterson
- Date: 4/12/2020
- Feedback in Detail:
All the plumbers who quoted for the job recommended Worcester! Even the boiler suppliers recommended them. Hence, we chose Worcester even though they were the most expensive. Boiler been installed now for one year and no problems. That’s all you want from a boiler, particularly approaching the winter!
- Name: Mr. Draycott
- Date: 3/12/2020
- Feedback in Detail:
The old boiler went bang and had a new Worcester boiler fitted. It’s brilliant, really pleased with it. Smaller and more efficient. The house is loads warmer and the water get much hotter than before. Went for the more expensive option but well worth it. It’s also very quiet as well. We had the magnetic filter put in as well. Worth every penny.
- Name: AI
- Date: 3/12/2020
- Feedback in Detail:
It has been a good unit. Very efficient and easy to use. Since installation last year we didn’t need to touch it at all. Hopefully the 8 years warranty would take care of any future problem (no problem at all now).
Our Installer done a great job with it. Over all very happy.
https://www.trustpilot.com/review/www.worcester-bosch.co.uk?stars=5&aspects=boiler
FAQs:
Will this boiler suit my home?
– The output rating of 18 kW is ideal for homes with 1 bathroom and a low heating and hot water demand but being a regular boiler might not make it an ideal choice for smaller properties.
Is a regular boiler right for my home?
– Regular boilers directly heat the central heating system and also produce hot water for a cylinder. As a hot water cylinder is needed, often fed by a cold water storage cistern in the attic, regular boilers aren’t suitable for smaller properties.
How efficient is this boiler?
– A seasonal efficiency rating of 92% and ErP A-rating for heat makes the Greenstar 18Ri a highly efficient unit.
Are there any options with this range of boilers?
– As well as this 18-kW model, the Greenstar range also includes boilers with many other outputs: 9 kW, 12 kW, 15 kW, 21 kW and 24 kW. The 9 kW, 12 kW and 15 kW models are all suitable for smaller homes with 1 bathroom that don’t have a high demand for heating and hot water. Meanwhile, the 18 kW, 21 kW and 24kW units can meet the heating and hot water demands of medium-sized homes.
What are the key features of the Greenstar 18Ri?
– Greenstar Ri boilers include frost protection, a simple boiler control for maximum control and full compatibility with Worcester Greenskies solar panels.
Could this boiler save me money?
– Thanks to being highly efficient, the Greenstar 18Ri will help to reduce energy bills and being compact and lightweight will keep installation costs to a minimum. It’s also compatible with Worcester Greenskies solar panels for further savings.
Where can this boiler be installed?
– As a wall-mounted compact boiler, the 18Ri can be installed within a standard cupboard to save space around the home. Plus, a frost protection feature means it can be installed in a loft or garage too.
How long is the warranty period?
– Available with a 5-year warranty as standard, that can be extended to 10 years when installed by a Worcester Accredited installer, you’ll be well covered by Worcester Bosch.
How efficient is the Greenstar 21Ri?
– If you’re looking for a heating system that could help to lower your energy bills then the Greenstar 21Ri is a great option thanks to a 92% efficiency rating and ErP A-rating for heat.
Is the output rating suitable for my home?
– The 21kW output rating makes the Greenstar 21Ri ideal for installation in homes with 10-15 radiators and 1-2 bathrooms.
Does the Greenstar Ri range include any other outputs?
– This range of regular boilers are available in a number of different outputs, including 12 kW, 15 kW, 18 kW and 24 kW in addition to this 21-kW model.
Is a regular boiler suitable for my home?
– A regular boiler should be installed into properties as part of an open vent heating system. This means that in addition to the boiler there will also be a cold-water tank in the loft and a hot water cylinder.
How long is the warranty period?
– A 5-year warranty is available as standard which can be extended to 7 or 10 years when certain terms and conditions are met.
What are the key features of the Greenstar Ri?
– Greenstar Ri boilers feature simple-to-use controls and can be paired with Greenskies solar panels. Plus, if you choose to have the boiler fitted into a garage or loft area, then the frost protection feature will prevent it from freezing during the winter months.
How big is this boiler?
– Thanks to compact dimensions of 600 x 390 x 270mm (HxWxD) the Greenstar Ri can be installed into a standard kitchen cupboard.
What’s the output rating?
– The Greenstar 24Ri has a 24-kW output rating, making it most suitable for smaller/medium sized homes that don’t have such a high demand for heating and hot water.
How efficient is the Greenstar 24Ri?
– A seasonal efficiency rating of 92% makes the Greenstar 24Ri a highly efficient boiler that also has an ErP A-rating for heat.
Is a regular boiler right for my home?
– Regular boilers (conventional or heat-only too) heat the central heating system directly and produce hot water for a cylinder. Due to needing a hot water cylinder, which is often fed by a cold-water storage cistern located in the attic, regular boilers aren’t suitable for smaller properties where space is limited.
Does this range come with any options?
– The Worcester Bosch Greenstar Ri range includes a number of models with varying outputs to help find the ideal unit for most homes. As well as this 24 kW model, there are also 9 kW, 12 kW, 15 kW, 18 kW, and 21 kW boilers available.
The 9 kW, 12 kW, and 15kW boilers are suitable for smaller homes with 1 bathroom and low demand for heating and hot water. Meanwhile, the 18kW and 21kW boilers can meet slightly higher demands.
Will this boiler save you money?
– Thanks to being highly efficient, the Greenstar 24Ri will help to reduce your energy bills. Plus, its compact size and light weight will lower the initial costs of installation.
Save even more money by pairing it with Worcester Greenskies solar panels.
Where can the Greenstar 24Ri be installed?
– As a compact wall-mounted boiler, Worcester Bosch have designed this boiler to fit within a standard kitchen cupboard. The inclusion of a frost protection feature means that it can be installed into a loft or garage too.
What are the key features of the Greenstar 24Ri?
– The Greenstar 24Ri comes with many features and benefits including simple boiler controls to give maximum control over the unit and the ability to pair it with Worcester Greenskies solar panels.
How long is the warranty?
– Available with a 5-year warranty as standard, which can be extended to 10 years when installed by a Worcester Bosch accredited installer, you’ll have peace of mind that you’re getting a highly reliable unit that won’t let you down.
How efficient is the Greenstar 30Ri?
– A seasonal efficiency rating of 93% makes this a highly efficient boiler that also has an ErP A-rating for heat.
Will this size boiler suit my home?
– An output rating of 30kW makes this Worcester Bosch boiler perfect for larger homes with 2+ bathrooms and a higher demand for heating and hot water.
What options are available in this boiler range?
– There’s plenty of choice when looking to install a Worcester Bosch Greenstar boiler. You not only have to install a gas boiler; LPG is also available. In addition, there are multiple output ratings in addition to this 30-kW model, including: 12 kW, 15 kW, 18kW 24kW and 27 kW boilers.
Where can this boiler be installed?
– Thanks to featuring flexible flues, the Greenstar 30Ri can be installed just about anywhere and being a compact wall-mounted unit means it can be installed within a standard cupboard, out of sight.
Will this money save me money?
– This boiler can save you money thanks to its high-efficiency rating allowing you to reduce your energy bills. As well as this it is an easy to install boiler allowing you to save the much-needed money on installation costs as well as saving you time
Is a regular boiler suitable for my home?
– Regular boilers directly heat the central heating system and also produce domestic hot water for a cylinder. As they need a hot water cylinder, often fed by a cold-water storage cistern in the loft, regular boilers aren’t suitable for smaller properties or homes where space is limited.
What are the key features of the Greenstar 30Ri?
– Features of the Greenstar 30Ri include frost protection to reduce freezing during the cold winter months, simple boiler controls for maximum control, and the ability to be paired with Worcester Greenskies solar panels.
How long is the warranty period?
– Greenstar 30Ri boilers are available with a 5-year warranty as standard with the option to extend this to 10 years when installed by a Worcester Accredited Installer.
DID YOU KNOW?
- It is also the smallest Worcester boiler; with compact dimensions that enable it to fit easily into a kitchen cupboard. The Greenstar RI should be used in an open-vent heating system that uses a hot water storage cylinder, plus it is fully compatible with the Greenskies Solar Panels.
- To reset the boiler: ► Turn the Central heating temperature knob anticlockwise to the “RESET” position and hold for approximately five seconds and then turn the knob back to the original temperature setting.
https://www.worcester-bosch.co.uk/support/literature/download/release/6720644685/12680
- The green light on a Worcester RI indicates the burner is operating. We’ve been called out to various boilers where the green light was off, but the rest of the boiler was working correctly.
- As a rough guide most apartments and smaller houses, with up to 10 radiators will require a 24-25kw boiler. A 28-30kw would be installed for a medium to large 3-4 bed house with up to 15 radiators, and a 33-35kw and a 40kw would be for a large house with anything up to 20 radiators.
https://www.traderadiators.com/blog/what-size-boiler-do-i-need
- Worcester Bosch continues to be the best gas boiler brand. Its customers are the happiest of any brand’s customers.
https://www.worcester-bosch.co.uk/products/boilers/which-best-buys
Conclusion:
Even though some might describe its controls as a little basic, the Greenstar Ri Regular is really easy to use and can be installed in around 4 hours or less. In addition to being a practical option if you have a lower demand for heating and hot water, this boiler is perfect if you live in an area where the mains water pressure is low.
It’s good to know that this appliance can capture wasted energy and re-use heat – and it can even cut your carbon footprint and energy bills in the meantime. You should also know that Worcester Bosch has won Which? ‘Best Buy’ for its gas boilers, so that should give you some confidence about the quality of this boiler’s efficiency and performance.
We should mention that this boiler might not be the best choice for homes with high ceilings and minimal insulation but like we said earlier, a responsible Gas Safe engineer should be able to help you determine which boiler will best suit your needs.