Best Worcester Bosch Boilers for Energy Efficiency Re January 30, 2023

Best Worcester Bosch Boilers for Energy Efficiency

Worcester Bosch 8000 Life Style

What are the best Worcester Bosch boilers?

In this blog, we look at the best Worcester Bosch boilers for energy efficiency. Worcester Bosch manufactures some of the best boilers on the market and has an exceptional reputation. 

In recent times, energy efficiency has become more important than ever before. Not only does having an energy-efficient boiler help you reduce your energy bills, but it also significantly helps to conserve the environment. How? Energy-efficient boilers consume less power and have lower CO2 emissions, reducing both the impact of global warming and your monthly bills.

Condensing boiler technology has reached new heights in terms of energy efficiency. Today, boilers are lighter, quieter, smaller, and even include next-gen features such as Smart Learning thermostats and Weather Compensation. With these distinct technological advancements, you can now save a lot of the resources you would otherwise spend on energy bills. Boiler manufacturers are creating highly efficient products and as such, if you are looking to buy a new boiler, now is the ideal time!

One of the most popular boiler brands is, of course, the Worcester Bosch brand. Their products have won over the hearts of customers from across the globe and even won various awards for their high quality and efficiency. Here are the top 5 most energy-efficient Worcester boilers.

Worcester Bosch Greenstar 24i Combi Boiler

Worcester Bosch Greenstar CDi Classic Installer On Phone Garage

The Greenstar 24i is a unique combination boiler that boasts a reasonable 24kW output rendering it a perfect fit for small to medium properties. With this fantastic Worcester Bosch boiler, you enjoy:

  • Simple boiler controls with clear information display
  • Suitable for homes where the heating system includes a hot water storage cylinder
  • Choice of controls enables greater comfort and economy*
  • Can be used with Greenskies solar panels for energy and cost savings
  • Low energy pump reduces electrical usage
  • Large Condensesure style siphon built into the boiler – eliminates frost risk 

View the Worcester Bosch Greenstar 24i ErP data

Worcester Bosch Greenstar 25i Combi Boiler

This is a direct replacement of the remarkably popular Worcester 24i Junior boiler. The Worcester 25i Greenstar is a combi boiler designed to suit small properties. It can service one bathroom and three bedrooms comfortably. Despite its similarity to the former, it comes with a new magnetic flap that opens to reveal an outstandingly new layout. With a new digital display, this boiler is also compatible with the assortment of Worcester Comfort controls and the Wave.

What’s more, you can be confident of its efficiency as this product fully complies with the new ErP Directives as well as guaranteeing similar performance to that of the 25Si Compact.

View the Worcester Bosch Greenstar 25i ErP data

Greenstar 25i Combi Boiler Key Features:

  • SEDBUK A-rated (over 90% efficiency levels)
  • Compact dimensions
  • ERP compliance
  • Hot water and central heating temperature control
  • Increased efficiency in standby mode (3.5 watts)
  • Wall mounting frame that enables you to conceal pipework from public view
  • Inbuilt CondenseSure Siphon
  • Vertical pre-piping kit
  • Multi-directional flue options
  • Lowest CO2 and NOx emission levels

Worcester Bosch Greenstar 25Si Combi Boiler


Next on the list is the Worcester Greenstar 25Si, which boasts a central 24kW heating output. It is a perfect central and hot water heating solution with the ability to service smaller properties extending to a single bedroom and three bathrooms.

What is perhaps its most remarkable feature besides its outstanding efficiency rate is its size. Its compact dimensions make this the smallest Worcester combi boiler ever! What’s more, the Greenstar 25Si offers you exceptional performance levels and reliability, as with all Worcester products.

Boasting a SEDBUK A-Rating, this boiler can quickly achieve a remarkable efficiency rate of well above 90%. This way you can significantly reduce your energy bill.

Greenstar 25Si Combi Boiler key features:

  • SEDBUK A-Rated (90.5% efficient)
  • Compact dimensions
  • Jig and 7 pre-plumb connections that allow quick installation
  • Inbuilt LCD for fault diagnosis and current operation status
  • 5-year warranty
  • Lightweight (32.9kg)
  • EMS-BUS compatibility

Worcester Bosch Greenstar 12Ri Regular Boiler

If you are looking for an efficient regular boiler with the capacity to effectively service your hot water and low heating demands, then the Greenstar 12Ri boiler is your best choice. Nonetheless, regular boilers offer central heating only so you need to install a hot water cylinder within the system to facilitate hot water provision.

It is built using a unique condensing technology that can effectively reduce your hot water and heating bills by between 15 and 20% annually; and if you are changing up from a much older G-rated boiler, the efficiency levels get even better at 30%. Imagine that!

Greenstar 12Ri Regular Boiler Key Features:

  • Over 90% efficient (SEDBUK A-Rating)
  • Light – 22.6Kg
  • Reversible return and flow pipes
  • Flexible installation courtesy of compact dimensions
  • Warranty: 5 years

Worcester Bosch Greenstar 15i System Boiler

It would be an injustice to complete this list without including yet another amazing product – the Greenstar 15i boiler. This boiler is ideal for small properties like bungalows and flats.

It offers A-rated efficiency, compact dimensions, and low-lift weight allowing you to effectually save a lump sum on your annual heating expenses while still delivering great reliability, even under the coldest conditions. Its high efficiency can reduce your annual heating bills by between 15 and 20% annually, with an even higher figure if you are replacing the traditional G-rated boilers.

Greenstar 15i System boiler key Features:

  • 700mm h x 330mm d x 400mm w
  • Pump and integrated expansion vessel
  • SEDBUKA A-rated (90.1% efficient)
  • A low-lift weight of 25kg
  • Compact dimensions allowing flexible installation
  • 5-year warranty

Worcester Bosch Greenstar 2000 Combi Gas Boiler

The Worcester Bosch 2000 series is a new addition to the Worcester Bosch family. It is a budget-friendly boiler range that combines sleek exterior designs with a powerful and reliable interior and not to mention excellent aftercare.

The Worcester Bosch Boiler 2000 is an A-rated model for energy efficiency. It has a seasonal efficiency rating of 93% for both central heating and hot water. This can save you money over the years. 

The Worcester Bosch 2000 series is only available as a combi boiler. It comes in two sizes; 25kW and 30kW. The 25kW model is perfect for small to medium-sized homes, such as flats with one bathroom.

On the other hand, the 30kW model is more powerful, it can cope with a higher demand for hot water. This makes it ideal for medium-sized homes with 2 bathrooms.

If you have a large home with over 15 radiators or two bathrooms that will be used simultaneously, then the 2000 series probably won’t have the power you need for your system.

The Worcester Bosch 2000 series is the quietest boiler manufactured by Worcester Bosch with an ERP rating of 43dB, which is quiet for an appliance. So if the boiler is located in a living area such as the kitchen, then this is an excellent option.

Greenstar 2000 key features:

  • ErP rating 93%: A-rated – This means that 93p in every £1 you spend on using your boiler is paying for the energy that is keeping you warm. 
  • Bosch engineered quality at an affordable price. The total cost of buying and installing the 2000 boiler is between (£1750 – £1850 including VAT) – incredible value for money!
  • The perfect size to fit in small places such as kitchen cupboards.
  • It is the quietest Worcester Bosch combi boiler (43dB), now you can enjoy your work-from-home midday naps!
  • Features Worcester Bosch innovative Quick Tap water-saving feature, which is activated with a quick opening and closing of a hot water tap. This helps to reduce water wastage in your home. 
  • Peace of mind with a 10-year guarantee on the primary heat exchanger.
  • Dimensions: 700mm x 300mm x 400mm.

Worcester Bosch Greenstar 4000 Combi Gas Boiler

The Greenstar 4000 is perfect for small to medium-sized homes with one bathroom. It features a modern new design, an easy to use full-colour text display and it’s quiet too. 

The Greenstar 4000 has a wide power range (25kW and 30kW) to meet all of your heating and hot water needs, whilst doing so efficiently.

In efforts to become more planet-friendly, the original polystyrene packaging used to package Worcester Bosch boilers has been replaced with recyclable cardboard. They have also ensured that all plastic packaging has been replaced with compostable bags which can be used in your garden or as a food waste bin. Although their packaging has been changed, their delivery still remains 5* by undergoing intense transport tests to make sure that your boiler is still protected and the new packaging is robust and keeps your boiler safe.

Based on the design of the famous, best-selling boiler on the market, the Worcester Bosch Greenstar i, Worcester Bosch have created a new and improved version, raising the bar with ease and speed of installation, commissioning, and servicing. The exterior of the 4000 series is very similar to that of the Worcester Bosch 8000 Life and Style boiler range, but it is significantly cheaper. This means you are getting all the great features and benefits of the Worcester Bosch Greenstar i, but with a little added spice!

Additionally, Worcester Bosch’s entire gas boiler range is able to run on a 20% hydrogen blend – so you can be confident it will run on mains gas for its lifetime. If you’d like to know more about hydrogen boilers, take a look at our blog.

Greenstar 4000 key features:

  • ErP rating 94%: A-rated.
  • A wide power range helps to reduce gas consumption and lower energy bills.
  • 100% planet-friendly packaging.
  • Innovative ‘Quick Tap’ water-saving function helps you reduce water waste.
  • The modern new design comes with an easy to use Full-text colour display LED screen.
  • Operates extremely well in low water pressure areas, ensuring powerful and warm showers.
  • One of the quietest combi boilers available (45dB).
  • Features wireless connectivity with the Bosch EasyControl.
  • Reminder settings, fault history and drain-down function.
  • Easy access to drain valve and pressure gauge.
  • Simple Switch option.
  • Instantaneous hot water, always available.
  • Suitable for small to medium homes.
  • Dimensions: 724mm x 400mm x 310mm.

Worcester Bosch Greenstar 8000 Combi Gas Boiler

WB 8000

Whilst looks aren’t everything, this boiler is the best looking of the bunch, so if your boiler is in a visible area then this big iPad-looking boiler is the one for you. Described by Worcester as the ‘Beautiful Beast’ it certainly lives up to its name. It’s by far the best-looking boiler out there and it’s the most powerful wall-hung boiler on the market, meaning there’s no need to hide it in a kitchen cupboard!

Worcester Bosch Life 8000 key benefits:

  • ErP rating 94%: A-rated
  • More power – outputs up to 50kW for combi and regular.
  • Easier installation, servicing and maintenance.
  • Robust and simple to fit.
  • Reduced lift weight compared to the CDi Classic.
  • A new clean, modern design.
  • Full wireless connectivity with the Bosch EasyControl.
  • Same pipe connections, flue and fixing points for ‘simple switch’ with CDi Classic.
  • 10-year guarantee (when purchased through WarmZilla)

Worcester Bosch Style 8000 key benefits

All the benefits of Life, plus: 

  • Stunning, design-led product aesthetics for contemporary homes.
  • A high-quality blend of precision engineering and class-leading heating and hot water performance.
  • Full-colour text display for simple diagnostics.
  • Innovative and intuitive boiler control display.
  • 10-year guarantee (when purchased through WarmZilla)

About Worcester Bosch

Worcester Bosch is a leading manufacturer of high-quality boilers. 

When it comes to heating and hot water solutions, Worcester Bosch is a well-known and respected brand in the UK and around the world. With over 50 years of experience in the industry, Worcester Bosch has established itself as a leader in the design, manufacturing, and distribution of high-quality boilers and controls. Whether you’re a homeowner or a landlord, Worcester Bosch has a solution to meet your needs.

At the heart of Worcester Bosch’s success is its commitment to innovation, quality, and customer satisfaction. The company invests heavily in research and development to ensure its products are at the forefront of the latest advancements in heating technology. This dedication to innovation has resulted in a range of boilers that are not only efficient and reliable but also easy to install, operate, and maintain.

Worcester Bosch offers a wide variety of boilers to suit every need, from compact combi boilers for small homes to larger system boilers for larger properties. Whether you’re looking for a high-efficiency model to save on energy bills or a condensing boiler for enhanced performance, Worcester Bosch has you covered.

In addition to its boilers, Worcester Bosch also offers a range of controls and accessories, including thermostats, programmers, and zone valves. These controls are designed to work seamlessly with Worcester Bosch boilers, providing optimal heating performance and comfort. They are also easy to use and feature intuitive displays and user-friendly interfaces.

Worcester Bosch is proud to offer excellent customer service and technical support to its customers. The company’s knowledgeable and experienced team is always on hand to answer any questions or provide assistance with installation and maintenance.

In conclusion, Worcester Bosch is a trusted and reliable choice for anyone in need of a high-quality boiler. With its commitment to innovation, quality, and customer satisfaction, Worcester Bosch is a brand you can trust to provide a solution that meets your needs and exceeds your expectations.

Worcester Bosch aftercare

Straight off the bat, Worcester Bosch is not only known for providing thousands of households with reliable and efficient central heating systems, but they also provide the best aftercare there is, and here’s why.

Worcester Bosch prides itself on its superb customer aftercare. It is something that you can clearly see throughout their excellent Trustpilot reviews, and that’s what earned them their 4.6 stars. If you’re not sold yet, read what their customers said about them:

“My choice of boiler was influenced by personal experience of Worcester Bosch. I have visited the factory, seen their impressive training facilities and production line. This is a good quality brand, made for decades in Britain. The 10 year guarantee backs up this reputation and was also important in my choice. The boiler has now been installed for 12 months.” 

“Our old boiler of nearly 20 years a Worcester was due for replacement. This boiler had given us great service during that period with very few problems..It was a no brainer to replace it with another Worcester and we opted for the green star far so good definitely hotter and without a doubt more energy efficient by far than the old boiler.”

Other ways to increase energy-efficiency

We’ve already written a great article with 7 tips for maximising the energy-efficiency of your boiler, but we’ll briefly cover them here.

  1. Regular Servicing
    The best way to ensure your boiler is performing efficiently is for it to have its MOT every year. A heating engineer will clear the filter and check it over to make sure it’s performing as it should.
  2. Turn it on
    It may sound strange but turn your heating on once a week during the summer. Like a car, your boiler is a complex piece of machinery that benefits from regular use. When the weather starts getting colder and everyone switches their boiler back on after a long rest is the busiest time of year for heating engineers.
  3. Keep it clean
    When you’re doing your spring clean don’t forget to give your boiler a little dusting. Like any machine, if it gets a lot of dust inside it, bad things will happen. Keep those vents clear too.
  4. Bleed your radiators
    If your radiators are colder at the top, it means there’s a good chance you have air in your system. This means your boiler is working to harder to heat your home as the radiators aren’t as efficient as they could be. Bleeding rads is simple and effective.
  5. Check your water pressure
    Have a look at the pressure gauge on your boiler, it should be around 1.5bar. If it’s lower it may need to be repressurised. Always take a look at the manufacturer’s guide just to be sure, not all boilers are the same.
  6. Insulate your pipes
    Help retain heat in your system by lagging pipes, it’s cheap to buy and over time will make a bit of difference to your energy-efficiency.
  7. Buy a new boiler
    All good things must come to an end. If your boiler is getting on a bit or you’re having to shell out on repairs more often than you’d like – it may be time to replace the old boiler. Replacing an old back boiler for a modern condensing A-rated boiler can save hundreds of pounds a year on your heating bill.

Smart thermostats

Another great way of saving money and increasing energy efficiency in your home is by using a smart thermostat. These devices are connected to your boiler and connected to your home internet. They allow you to control your heating from your smartphone, tablet, or Alexa.

Forgot to turn your heating off? Just log into the app on your phone and you can do it from anywhere in the world. Smart thermostats give you more control over your heating and lead to savings on your heating bill.

We’ve already reviewed the Nest Learning Thermostat, which learns from how you use it – what rooms you occupy and when and adjusts your heating accordingly to save you money. Pretty clever eh?

If you aren’t sure what features a smart thermostat has to offer then here are 8 features of a modern smart thermostat to get you started.

Every WarmZilla boiler installation comes with a Salus smart thermostat as standard, they are a solid smart thermostat but they lack the advanced features of a Nest learning thermostat (which would add a bit more to the final price).


All the Worcester boilers above are high-performance appliances that would effectively help you save a significant amount of money on your annual energy costs.

All modern condensing boilers offer 90%+ energy-efficiency, compared to back boilers which you’d be lucky to see 70% efficiency.

Which boiler you require depends on the size of your home and what hot water and heating demand you have. If you have a 5 bedroom home with multiple bathrooms being used simultaneously then you will need a more powerful kW boiler to cope with demand.

If you want more help understanding the kW needs of your home then, we’ve written a useful article on what size kW boiler would be best suited for your home.

However, the beauty of the WarmZilla survey is that you don’t need to know anything about kW sizes – our survey will calculate exactly what size boiler you need based on your answers to some very simple questions.

So what are you waiting for? Get a fixed price quote on a new boiler in minutes.

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