Worcester Bosch 4000 boiler review

Worcester 4000 review

Worcester 4000 Review – Everything you need to know about Worcester’s 4000 boiler range

If you were to ask a boiler engineer which is one of the most installed boilers, we think you’d be on to a pretty safe bet to put your money on the Worcester Bosch 4000 boiler.

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With glowing reviews from homeowners and a consistent place in the Which? Best Buy choices, this leading boiler manufacturer places quality at the top of their company aims.

So, it came as a bit of a surprise when they decided to mothball their best-selling boiler, the Greenstar i. To take that bold decision, we knew that Worcester Bosch must have something special up their sleeve, and they did, in the form of the Worcester 4000.

This new model is available as both a combi and a system boiler range, and it was launched in May 2021. Need to know, right now, what this replacement offers above the Greenstar i?

Well, there’s a new technology, a sleek design, and a compact size. In fact, this new kid on the block has everything it needs to become Worcester Bosch’s latest top seller.

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Worcester 4000 boiler: Key features

  • A mid-range model
  • Quieter operation compared to the Greenstar i
  • Compatible with Worcester Bosch controls and products such as Nest, tado and Hive
  • An excellent choice for small to medium-sized homes
  • Easy access for servicing with its removable side panels
  • Maximum of a 10-year guarantee
  • ErP rating 94%: A-rated
  • Dimensions: 710 x 400 x 310

Worcester Bosch 4000 combi boiler review

For smaller homes with one bathroom, getting the best combi boiler with an instant hot water supply is a great choice. The Greenstar 4000 is available in two different power outputs.


A great choice for smaller homes with up to 10 radiators, the 25kW combi boiler provides a flow rate of 10.5l/min and a heat output of 25kW.


For larger homes with up to 16 radiators, the 30kW option is a better choice. That extra 5kW of power increases the flow rate up to 12.3l/min.

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Worcester Bosch 4000 system boiler review

For larger homes with more than one bathroom, you may find that a combi just isn’t able to provide the hot water you need. That’s when a system boiler comes in with its hot water storage cylinder.  

There are five different power outputs available for the 4000 system boiler as below:

  • 12kW
  • 15kW
  • 18kW
  • 21kW
  • 24kW

Worcester Greenstar 4000 efficiency

Boiler efficiency is high up on the list for both boiler manufacturers such as Worcester Bosch and every homeowner. When we have an efficient boiler, it burns less fuel, which, in turn, means that fewer carbon emissions are released into the atmosphere.

Energy efficient Worcester

This, in turn, is great news for the environment as carbon is believed to be a key reason behind climate change.

There’s another significant advantage too, in that your hard earnt cash isn’t going to going to be going up in flames in boiler inefficiency.

What does the efficiency level mean?

Both the combi and system models achieve an impressive 94% level of efficiency.

Efficiency levels are calculated by assessing how much of the fuel, so the gas, LPG or oil, is turned into usable energy and then how much is wasted during the heating process. 

At 94% efficiency, that means that just 6% of the energy used to heat the water is lost during the heating process. And you’ll see that 6% as the gases being emitted via the flue pipe. If we think about this in financial terms, for every £1 you spend on energy to heat your home, 6p of that is lost to the heating process.

All new boilers now need to be at least 90% efficient, but in the past, it wasn’t unusual for boilers to have efficiency levels of between 60 to 70%. If you currently have an old boiler, 40% of your energy costs could be wasted! Now is the time to get a new boiler quote.

ErP rating what is it?

All of the boilers in the 4000 range, both system and combi, achieve an ErP rating of ‘A’.

ErP stands for the Energy Related Products Directive. Launched by the EU, its main aim I to phase out all inefficient household appliances. The ErP makes it easier to know which products are more efficient, resulting in reduced carbon emissions and the opportunity to save on energy bills.

So, that means that boilers must be labelled with their certified efficiency level, and that goes from G, which is the lowest level of efficiency right up to A+++ for the highest efficiency.

The directive also introduced Ecodesign, a set of new regulations that manufacturers have to follow. This meant that those heating systems that didn’t meet the required standards had to be phased out by the boiler manufacturers.  

Worcester 4000 – Key features reviewed in detail

Simple switch

Do you want all the great features of a new boiler but none of the hassles of installation? Well, Worcester Bosch has done everything they can to make it as pain-free as possible with what they’ve called Simple Switch. That means that you’re looking at seamless swapping out for the following boilers:

  • Greenstar i Junior combi (2005 – 2013)
  • Greenstar i Junior combi (2013 – 2015)
  • Greenstar Si combi (2005 – 2013)
  • Greenstar i ErP (2015 – 2021)
  • Greenstar i System (2005 – 2015)
  • Greenstar i System ErP (2015 – 2021)

Quick tap

When you turn on your hot water tap, what do you do while you wait for the heated water to appear? Wait impatiently? Run your hand back and forth through the water, waiting for that flow to go from cold to lukewarm and then finally to hot? And all the time that cool water is running into the waste pipe.

Quick Tap allows you to turn your hot water tap on and then immediately turn it off. That tells the boiler that you need hot water. Wait for just twenty seconds, turn the tap back on, and you’ll have hot water flowing straight away.

No more wasted time stood at the sink waiting for the hot water to arrive and much less wasted water.

Enhanced levels of efficiency

The Greenstar 4000 is the most environmentally friendly boiler available from Worcester Bosch. This is a boiler that can modulate at 1:10. That means that the power output can be reduced to 10% of its maximum output.

So, a 30kW boiler can drop down to 3kW when there are low demand levels on the heating system. Not only does it make the 4000 incredibly efficient, but it also means lower fuel bills and less wear and tear on the boiler.

Greater control

Taking control of our heating needs to be made easy, and that’s precisely what Worcester Bosch has done. With Bosch EasyControl, the Greenstar 4000 can be controlled wirelessly no matter where you are. It also allows you to track your energy usage. Drop the temperature even by just a single degree and then see the impact on your energy bill.

Then there are thermostatic radiator valves. Installed onto each radiator, they allow you to set the temperature for each individual room. Prefer your bedroom cooler and your living room warmer? Now you can have that with Bosch EasyControl; all set up from the app on your mobile phone.

If you have Alexa or Google Home Assistant, then you can also control the heating with voice commands.

99.9% recyclable product packaging

Yep, you read that correctly. The Worcester Bosch Greenstar 4000 comes in 99.9% recyclable packaging. This is a company that has already made a strong commitment to reducing the impact that they have on the environment. They’ve already achieved carbon neutral status, but it looks like that’s not good enough for them!

Full-colour text display

The LCD display panel combined with push-button controls make the 4000 much easier to programme and find information about the boiler status. This may seem like a relatively minor detail, but if your boiler isn’t working as it should, the last thing you want to deal with is confusing information.

Intelligent filling system

This is a feature that’s been carried through from the Greenstar i range. The intelligent filling system is a software programme that ensures that the boiler pressure is always at its most efficient level.

So, that means that if the pressure is lower than it should be, the internal filling valve will open, and it automatically fills the heating system to the correct level and then switches back off again.

If the pressure becomes too low, so maybe through a leak in the heating system, then it will alert you to the problem 

The intelligent filling is only available on the Greenstar 4000 combi boiler and not on the system version.

Quiet Operation

The Greenstar i was already quiet when it was operating, so it is pretty impressive for the 4000 to make even less noise. The combi version, for example, operates at 45dB. With a normal conversation being around 65dB and a vacuum cleaner being 75dB, the 4000 is not going to be annoyingly noisy.

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Is your boiler futureproof? The Greenstar 4000 is!

The UK is known for having a world-leading gas network, and because of that, we’ve all become very reliant upon it. In fact, 85% of homes and businesses use natural gas for their heating needs, including their hot water supply and for cooking.

The problem is that if we’re to tackle the climate emergency, then we need to dramatically reduce our household carbon emissions. But, to do that we need to stop using natural gas.

The Energy Savings Trust estimate that household carbon emissions just from our heating, need to drop from close to 3 tonnes a year right down to 138kg, and that needs to happen by 2050.

If a blend of gas and hydrogen is pumped through the gas grid, that could save nearly 6 million tons of carbon dioxide emissions every year. That’s the equivalent of 2.5 million cars being taken off the road.

Like all of the Worcester Bosch range of boilers, the Greenstar 4000 can already run on a 20% hydrogen blend. With a government commitment in place to make this happen by 2025, you’ll be able to relax knowing that there’s no need to make any alterations to your heating system.


The warranty that comes with a new boiler is there to give you peace of mind in your new purchase. Should anything go wrong, then you know that you can simply call the helpline, and an engineer will be dispatched.

However, there are some significant differences between the warranties offered by different boiler companies. And of course, there’s also the need to take a close look at the small print in the terms and conditions!

For the Greenstar 4000, Worcester Bosch offers a generous guarantee of up to ten years. So, that’s:

  • Standard guarantee – 7 years
  • Guarantee when a Greenstar System Filter is fitted – 8 years
  • Guarantee when a Greenstar System Filter is fitted, and payment made of £150 – You can get 10 years

Guarantee terms and conditions

As with all cover, whether that’s a guarantee or a warranty, it’s essential to understand the terms and conditions. For the Greenstar 4000, you need to ensure:

  1. The boiler must be installed and commissioned by a competent and officially certified installer such as a Gas Safe registered engineer
  2. The boiler must be registered within 30 days of the boiler installation
  3. The boiler is installed into a domestic home
  4. A gas safe engineer must service the boiler on an annual basis

Worcester Bosch Greenstar 4000 – Should you buy one?

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’re in no doubt that the 4000 will become the next top-selling boiler in the Worcester Bosch range.

So, is the 4000 the right model for you? We think it’s got a huge amount of appeal for small to medium-sized homes. However, getting a personalised quote is a great way of being provided with a choice of boilers that are going to meet your heating and hot water needs.

You can then ensure you get the best new boiler cost from Boiler Central, which are 5-star rated on Trustpilot with 1,000s of reviews.

Simply provide a few household details and we’ll do the rest for you, get a price online with our free quotation tool below:

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