Worcester Bosch Combi Greenstar 4000 combi boiler review

The Worcester Bosch Combi Greenstar 4000 boiler comes with a 10-year guarantee. (Image credit: Worcester Bosch)

The Worcester Bosch Combi Greenstar 4000 is the newest addition to the Worcester Bosch combi boilers range and was designed with major improvements to the previous Greenstar i model, including a higher hot water output and quieter operation. The 4000 also features a new look: a sleek curved edge case, digital display and simple push control buttons. Removable side panels allow for easy servicing and the boiler is backed by a 10-year guarantee (when fitted by an accredited installer).

It’s compatible with the Bosch EasyControl system. This allows you to take full control of your home’s temperature via your mobile phone. You can even control your central heating remotely, so you can use energy efficiently. The system can be operated with voice commands via Alexa or Google Home, too.

Speaking of efficiency, the Worcester Bosch Greenstar 4000 has an efficiency of 94%, which means that only 6% of the energy used to heat the water in your boiler is lost.

That’s not the only energy-reducing feature this boiler has. The Greenstar 4000 combi boiler can modulate at 1:10, meaning you can reduce the power output to 10% of its maximum output during periods of low demand. This not only makes your boiler highly energy efficient (and cuts your fuel bills) but reduces the wear and tear on your boiler.

We also like the Greenstar 4000’s new ‘Quick Tap’ feature which eliminates the need to wait with a running tap for the water to come through hot. Simply turn your tap on and immediately turn it off to let your boiler know you need hot water. Within seconds, you’ll have flowing hot water.

According to Worcester Bosch, the Greenstar 4000 is the company’s most environmentally friendly boiler to date. It can modulate at 1:10, which means a 30kW model can run effectively at 3kW if needed, reducing energy wastage.

The Worcester Bosch Combi Greenstar 4000 is wirelessly compatible with the Bosch EasyControl thermostat (sold separately), which enables you to control the temperature of individual rooms in your home remotely via your phone, reducing energy usage even further.

• Guarantee options: Five-year standard guarantee. 10-year guarantee when installed by an accredited installer.
• Price range: From £1,200 to £2,500
• Efficiency rating: A
• Output rating: 25kW and 30kW

The Worcester Bosch Combi Greenstar 4000 boiler is compact and can be wall-mounted to save space in the home. (Image credit: Worcester Bosch)

Highlights: Worcester Bosch has been the winner of the Which? Best Buy Award for 10 years running.

Key benefit: Excellent energy-saving technologies, including wireless controls, ‘Quick Tap’ functionality and 1:10 modulation.

Fuel: Gas, hydrogen-ready (20% blend).

Flow rate: 10.2 litres per minute.

While we have a lot of positive things to say about the Worcester Bosch Combi Greenstar 4000 boiler, it might not be the best fit for your home and energy needs. Always consider the pros and cons before making a final decision.

Choosing the Greenstar 4000 has the following benefits:

• ‘Quick Tap’ feature: With the ‘Quick Tap’ feature, you will have hot water readily available without delay or running the tap, reducing water wastage and energy consumption.
• Environmentally friendly: This boiler is A-rated for energy efficiency (for both central heating and hot water). What’s more, 99.9% of the packaging used to transport and deliver your boiler is recyclable.
• Greater control: The Greenstar 4000 range is compatible with a wireless connected smart thermostat, the Bosch EasyControl. This enables you to keep an eye on your energy usage and control your central heating remotely, room by room. You can also use voice commands to manage your Bosch EasyControl thermostat with Alexa or Google Home Assistant. The Bosch EasyControl system is sold separately.
• 1:10 modulation: The Greenstar 4000 combi boiler can modulate at 1:10, which means you can reduce your energy output to 10% of its maximum output, reducing your fuel bill as well as wear and tear.
• Quiet operation: The Greenstar 4000 range has been awarded Quiet Mark accreditation. This means your boiler will operate quietly without disturbing anyone in your household.
• Simple Switch: You can upgrade your Greenstar i boiler to the Greenstar 4000 combi through Worcester Bosch’s Simple Switch program.

This boiler does have some drawbacks, including:

• Stock shortages: According to Boiler Central, there have been some supply issues related to the Greenstar 4000 due to microchip shortages. Given the popularity of this model, shortages may be likely.

Not suitable for large homes: The Worcester Bosch Combi Greenstar 4000 isn’t powerful enough to heat large homes with more than two bathrooms or ten radiators.

Simple displays will show you how well your boiler is performing. (Image credit: Worcester Bosch)

Combination (or “combi”) boilers provide hot water and central heating from a single, compact unit. Unlike a system boiler that isn’t fitted with a hot water exchanger and needs a cylinder to work, the combi boiler heats water directly from the mains whenever you turn on a tap.

This generally makes it more cost-effective because your water is heated instantly rather than being heated and stored in a cylinder. Water is delivered at mains pressure, which means you can enjoy hot, powerful showers.

Another bonus is that combi boilers are generally a lot more compact as they don’t require as much pipework or a separate hot water storage cylinder. This makes them ideal for smaller properties.

The Worcester Bosch Greenstar 4000 is a good option for smaller homes with limited space and energy requirements. However, it won’t suit properties with more than two bathrooms.

You may want to consider the Greenstar 8000 Style combi boiler if you have a larger home with higher energy needs. This boiler comes with higher power outputs than the 4000: 30kW and 45kW. Like the Greenstar 4000, the 8000 Style is available as either a combi or system boiler. You can expect to pay around £1,400 for this boiler (unit only including VAT), so it’s more expensive. However, this model comes with a 12-year guarantee when installed by an accredited installer, which is two years longer than the Greenstar 4000’s longest available guarantee.

Alternatively, you might want to look at the Vitodens 111-W. It’s a lot more powerful than the Greenstar 4000, meeting the heating demands of up to 15 radiators with its 34kW domestic hot water (DHW) output. It comes with a long 12-year warranty period if you have it installed by an approved installer. Prices start at £1,575.

We have also heard very good things about the Vaillant ecoTEC Green iQ 835 combi boiler, which has a 94% efficiency rating, an A rating for heat and hot water and a number of eco-friendly features designed to save you money on your energy bills. You can expect to pay around £1,425 for this boiler (excluding installation).

Worcester Bosch Greenstar 4000 boilers are considered mid-range in terms of pricing and performance. While installation costs can vary, you can expect to pay the following for your boiler:

The Worcester Bosch Combi Greenstar 4000 boiler has a control panel that makes it even easier to use. (Image credit: Worcester Bosch)

The Greenstar 4000 comes with a simple and easy-to-access control panel. It comes with intelligent filling, which means that if pressure is lower than it should be, the filling valve will restore it to the correct level. If the drop in pressure is due to a leak in the heating system, the control panel will tell you.

Have your boiler serviced at least once a year to avoid running into any issues. If your boiler is out of warranty, it’s a good idea to opt for Worcester Bosch’s service plan to ensure you’re covered. You should also bleed and balance your radiators at least once a year to keep your heating system in top condition.

“Worcester Bosch is a huge household name in the boiler game for a reason . . . reliability!

If you ask most people what the best combi boiler is, the Worcester Bosch group will come up every time. Worcester Bosch covers quite a range of boiler types and features, which means that they are suited to plenty of different situations. However, they are also consistent in terms of quality, so there is not any risk of a certain model being extremely poor or unreliable.”

• Iheat.co.uk

“We must admit that we were more than a little surprised when Worcester Bosch decided to replace their top-selling boiler replacement range. But now that we’ve seen the specification for the 4000, it all makes much more sense. This is a boiler that’s been carefully designed to give you all the functionality you need while still being incredibly user-friendly to use and providing high levels of efficiency. . . . We think it’s got a huge amount of appeal for small to medium-sized homes.”

• Boiler Central

“The Greenstar 4000 is a brand new arrival to the Worcester Bosch range of combi boilers, designed to replace the best-selling Greenstar i range. The Worcester Bosch 4000 offers everything the i range did, but with some major improvements, including a quieter operation and a higher hot water output. The 4000 benefits from a new, sleek curved edge case, user-friendly digital display and easy-to-use push control buttons, a major improvement on the boring square boxes of old.”

• Heatable 

“I installed a Greenstar 4000 30kW Combi NG boiler in Sep 2021. Smart-looking efficient boiler. Fits nicely in the gap next to the kitchen wall units. Worcester Bosch gave me eight years guarantee as it was installed by an approved installer. Boiler did develop a small internal leak six months later due to a faulty AAV (automatic air vent) but Worcester Bosch dispatched an engineer within a day and rectified the fault. I am pleased with its performance so far. Good customer service. I am giving four stars only because the boiler developed a fault.”

• Vince, Trustpilot 

“Very pleased with the boiler, easy-to-navigate menu, and it’s saving us money which is essential at the moment.”

• Norman, Trustpilot

“Having a Worcester Bosch boiler installed was the best money I have ever spent. Heating bills are so much cheaper now, they are so reliable. After experiencing so many other boilers in various houses and the money I have had to pay out for repairs etc. I wish we had changed to Worcester Bosch if I move again I am getting one fitted straight away. I love Worcester Bosch.”

• Susan, Trustpilot

The Worcester Bosch Greenstar 4000 combi boiler is a low-maintenance, easy-to-install and easy-to-use combi boiler with a fair guarantee, energy-saving technology and a decent flow rate. Its modern design and quiet operation make it perfect for smaller homes where your boiler may need to be on display, while the optional EasyControl add-on lets you control your boiler remotely.

Worcester Bosch does not manufacture the cheapest boilers on the market, but the Greenstar 4000 combi starts at a fair £1,200. This makes it an accessible choice for many homeowners. 

The 25kW model is a good choice for smaller homes with 10 radiators or less, while the 30kW is recommended if you have two bathrooms.

Our methodology

To compile this Worcester Bosch Combi Greenstar 4000 boiler review, we read hundreds of professional and customer reviews from sites like Trustpilot, and looked at technical documentation, professional write-ups, brochures and media sites. We then rated this boiler against the following criteria for a total score of 100 points:

• The warranty period offered by the brand, for a total of 10 points;
• The overall reputation of the brand based on online reviews, for a total of 15 points;
• Trustpilot reviews, for a total of five points;
• Awards and accolades (eg, Which? Best Buy Awards), for a total of five points;
• Customer service performance, for a total of 10 points;
• The price range, for a total of 15 points;
• Efficiency ratings, for a total of 15 points;
• Installation and maintenance network and reviews, for a total of 15 points; and
• Overall performance (temperature, maximum flow), for a total of 10 points.