Category - Boilers
Guide author photo

Will Scholfield, Engineer

15 May : Updated 15 May ● 8 min read

Worcester Bosch Greenstar 4000 - boiler review

Worcester Bosch boilers are one of the UK's most trusted, best-selling boiler manufacturers, and for good reason. The company makes some of the most reliable and efficient boilers on the market.

If you're looking for a new boiler, you can't go far wrong with a Worcester Bosch boiler, and one of the brand's most popular models is the Greenstar 4000.

Launched in 2021, the Greenstar 4000 comes in combi and system boiler models, and replaced the Greenstar i - Worcester Bosch's best-selling boiler.

Here, we take an in-depth look at the Greenstar 4000, exploring its cost, reliability, energy efficiency, performance and ease of use to help you decide whether this boiler is the right choice for your central heating system.

We've rated each section out of five stars, so at the end of this boiler review, we'll have a final score out of 25 stars. If you want to see our ratings now, jump to the results.

First, let's discover the key features the Worcester Bosch Greenstar 4000 has to offer.

Worcester Greenstar 4000: key features

The Greenstar 4000 comes in various sizes, including 25 and 30kW and is Worcester Bosch's mid-range boiler, sitting between the 2000 and 8000 models. The boiler's output and size are ideal for small and medium-sized homes.

A convenient feature if you're upgrading from a Greenstar i boiler is SimpleSwitch, which means the 4000 will fit into the existing area left by your old condensing boiler. This reduces disruptions and the time it takes to install the boiler.

Other notable specifications, that we explore in further detail below, include:

  • The Greenstar 4000 is one of Worcester Bosch's quietest combi boilers and has even been awarded Quiet Mark accreditation.
  • 10-year manufacturer-backed guarantee.
  • A-rated for efficiency, with a score of 94%.
  • Compatible with Worcester Bosch controls and third-party controllers, like Google Nest.
  • Accessible side panels enable the boiler to be serviced and repaired more easily.

Embed video:

Learn more about the Greenstar 4000

cover for videos

Worcester Greenstar 4000 review

With around 7 million boilers installed nationwide, Worcester Bosch is one of the most recognised and respected companies in the sector. But how does the Greenstar 4000 boiler stack up in key categories like reliability, cost and efficiency? Let's find out.

Worcester Bosch Greenstar 4000: Reliability

Worcester Bosch has built its reputation on producing highly reliable boilers, and the manufacturer-backed 10-year guarantee is a sign of the Greenstar 4000's quality.

If your boiler does require servicing or maintenance, the removable side panels mean all key components can be accessed quickly and efficiently, so if your engineer charges by the hour, this can save valuable time and money.

For further proof that Worcester Bosch is a reliable boiler manufacturer, the company is rated excellent on Trustpilot, with an average rating of 4.6 out of 5 from over 40,000 reviews.

The annual boiler report from Which? has also revealed that Worcester Bosch is the most reliable boiler brand on the market based on customer satisfaction, product quality and after-care. As a result, the boiler company has been endorsed as one of Which’s Best Buy Brands for the last 14 years. 

Reliability score: 5/5

Worcester Bosch Greenstar 4000: Efficiency

The Greenstar 4000 has received an ErP rating of A. So, if you want to upgrade your old boiler, a Greenstar 4000 could save you money on your heating bills and reduce gas consumption.

More specifically, the boiler's energy efficiency is 94%, so just 6% of the energy used to heat the water is lost during the heating process. If you equate this to money, that means for every £1 you spend on heating your home, just 6p is lost.

Another feature that helps to save energy and water is the Quick Tap addition. Turn your hot tap on and off to start the boiler up, leave it for 30 seconds before turning it back on, and you'll have hot water without running the tap and wasting water. This may seem like a small detail, but it can make a big difference when people all around the country are doing the same thing.

The boiler's power can be reduced to 10% of its output to maximise efficiency further, through a process called modulating. So, if you have the 30kW boiler, it can automatically reduce the power to 3kW. Modulating the performance in this way means that when there is little or no demand for the boiler, e.g. during the summer months, you won't be wasting electricity or money on unnecessarily high energy bills.

Read more about how efficiency ratings are calculated in 'Boiler efficiency: a complete guide'.

Efficiency score: 5/5

Worcester Bosch Greenstar 4000: Performance

To maximise performance, the Greenstar 4000 has an optional extra intelligent filling valve that adds boiler pressure to keep your system at the optimal amount.

The boiler's intelligent filling system doesn't stop there, as it will notify you if the boiler is losing too much pressure so you can call a Gas Safe engineer to come and inspect the problem before it gets worse.

One of the things that makes the Greenstar 4000 such a good choice for smaller homes is its flow rate. The 25kW option provides 10.5L per minute, making it an excellent choice for those with one bathroom and up to 10 radiators.

If your home has higher hot water demands, i.e. more than one bathroom, the 30kW option can provide 12.3L per minute and comfortably service your home.

Is a frozen condensate pipe an all too common occurrence with your current boiler? Well, 
Worcester Bosch has thought of this, too. The Greenstar 4000 is specially designed to avoid freezes when the temperature drops, so you and your home can remain toasty and warm whatever the weather.

If your current boiler is struggling in the cold weather, discover how to fix a frozen boiler condensate pipe in our guide.

Another key performance benefit to the Greenstar 4000 is that it's less noisy than its predecessor, the Greenstar i. The combi version of the 4000 operates at just 45 decibels - about the same loudness as a library, and they're known for being very quiet. This quieter operation makes the Greenstar 4000 one of the quietest combi boilers on the market, so if you're fed up with your old boiler clunking and banging, this could very well be the upgrade your ears desire.

Performance score: 5/5

Worcester Bosch Greenstar 4000: Cost

When you're looking for a new boiler, cost is typically one of the significant factors you're going to consider. Compared to some brands in the boiler industry, the Worcester Bosch range carries a premium price tag, but the quality of the products certainly justifies this.

When shopping for a new appliance, it's important to note that the cheapest boiler upgrade may not be the most suitable for your home. Instead, you need a boiler that can handle the demands of your home and offer good value for money.

To select the right boiler, enter your postcode to begin. We ask for a few key details about your current heating system and the size of your home, then recommend suitable boilers for you. It's that easy.

With BOXT, you can have a Worcester Bosch Greenstar 4000 installed as early as tomorrow, so what are you waiting for? Get a boiler quote now

Additionally, when you get your new boiler installed by BOXT, everything’s included in the price, like a wireless room thermostat and magnetic system filter, so you can manage your boiler's heat output while the filter keeps the system clean. We’ll also carry out a chemical flush as standard to ensure your central heating system is clear of any dirt, debris, rust, and other contaminants.

Cost score: 4.5/5

Worcester Bosch Greenstar 4000: Ease of use

With a full-colour LCD display panel, the controls of the Greenstar 4000 are easy to follow and programme. While the ease of use may not be at the top of your list of boiler must-haves, it is a crucial consideration, especially if something goes wrong.

Plus, it's compatible with a range of thermostats to schedule your boiler's heating for optimal performance and comfort.

Ease of use score: 5/5

Final scores

As we have explored above, Worcester Bosch boilers are some of the most reliable on the market, and the Greenstar 4000 heating systems continue this trend as one of the best boilers available.

With a final score of 24.5/25, the energy-efficient Greenstar 4000 is a fantastic option for your next boiler. And, if you're thinking of upgrading, look no further than BOXT.

Buy a Worcester Bosch Greenstar 4000 from BOXT

If you need a new boiler installed at your home, look no further than BOXT. With a quality range of combi and system appliances, including the Worcester Bosch Greenstar 4000 and installation as quickly as tomorrow, you could soon be saving on your energy bills and reaping the benefits of a new boiler.


Share this post