Best 40kW Combi Boiler: 2025 Review & Price Guide

40kW combi boilers are compact units capable of providing central heating and hot water to a home without the need for a bulky water tank.

A 40kW boiler is considered a high-powered option, ideal for properties with above-average heating needs, like homes with two bathrooms, for example.

If you’re confident that a 40kW combi boiler is the right choice, check out our top recommendations and prices for 2025.

5 Best 40kW Combi Boilers

Before we get into the details, here’s a quick overview of our top recommendations:

Boiler model	Cost of unit	Cost including installation	Efficiency rating
Worcester Bosch Greenstar 8000	£1,495	£2,295 – £2,795	94%
Baxi Platinum Combi 40	£1,276	£2,076 – £2,576	92%
Ideal Vogue Max	£1,645	£2,145 – £2,645	91%
ATAG i40C	£1,500	£2,000 – £2,500	94%
Navien NCB	£914	£1,414 – £1,914	94% – 98%

1. Worcester Bosch Greenstar 8000+

The Worcester Bosch Greenstar 8000+ is brought to you by one of the leading brands in the UK. 

This model is the most powerful boiler in the Worcester Bosch range as well as the most stylish. Featuring a sleek design and top-of-the-range technology, the compact unit will look great in any home.

Key specs:

• Efficiency: 94% A-rated ErP
• Fuel type: Gas or LPG
• Dimensions: 780 (h) x 440 (w) x 365 (d)
• Hot-water flow rate: 15 litres per minute
• Warranty: 12 years

Top features include:

• Clear colour touchscreen display
• Wireless connectivity and compatibility with Bosch’s EasyControl smartphone app for remote heat control
• 1:10 modulation to efficiently match heating demands
• Greenstar Intelligent filling system: The boiler can automatically refill while maintaining optimum pressure
• Hydrogen-ready combi boiler: Able to handle potential future hydrogen level increases in your gas supply

Price: The Worcester Bosch 8000+ costs around £1,495 for the unit alone. Combined with installation costs, you can expect to pay around £2,295 – £2,795 in total.

Worcester Bosch has long been a firm favourite amongst UK homeowners. It’s an excellent choice for anyone looking for a modern, efficient, and future-proof heating solution. 

We especially love the sleek, contemporary design and user-friendly, convenient features.

With a lengthy warranty, this boiler offers reliability, efficiency, and peace of mind, making it our top combi boiler recommendation for larger homes.

2. Baxi Platinum Combi 40

Baxi boilers are well-respected and highly rated boilers. The Platinum is ideal for larger homes that want to prioritise efficiency and enjoy lower energy costs.

Although this is the most powerful combi boiler in Baxi’s Platinum range, its compact size means it can fit seamlessly into any environment. 

Noise needn’t be an issue, either, since it operates extremely quietly.

Key specs:

• Efficiency: 92% A-rated ErP
• Fuel type: Gas
• Dimensions: 780 (h) x 450 (w) x 345 (d)
• Hot-water flow rate: 16.4 litres per minute
• Warranty: 10 years

Top features include:

• Intuitive interface and optional mechanical 24-hour timer
• Wifi-enabled, the Baxi uSense 2 smart room thermostat allows heat control from any device
• Built-in anti-frost thermostat
• Super quiet operation
• Adey Micro 2 Filter included
• Easy fill top-up system

Price: The Baxi Platinum costs around £1,276 for the unit. Expect to pay around £2,076 – £2,576 for the boiler and installation together.

We like that this boiler packs a punch but remains small enough to fit in a kitchen cupboard – something you don’t see often in high-output boilers.

The anti-frost thermostat is useful if you plan to situate the boiler in a colder area of the home, such as the garage.

All in all, it’s a small but mighty unit.

3. Ideal Vogue Max

Ideal is known for making premium products. The Vogue Max range is no exception.

You can expect high-quality components used in this boiler for a long-lasting, reliable heating solution. 

Boiler replacement and repair needn’t be a worry, thanks to a choice of two extra-long warranties.

Key specs:

• Efficiency: 91% A-rated ErP
• Fuel type: Gas (LPG conversion kit available separately)
• Dimensions: 740 (h) x 445 (w) x 330 (d)
• Hot-water flow rate: 16.4 litres per minute
• Warranty: 10 or 12 years

Top features include:

• Full-colour large LCD with plain text and graphics
• Text support for fault modes
• Service timer
• Comes with an Ideal System Filter 
• Compatible with Ideal remote control systems
• Anti-frost thermostat

Price: The Ideal Vogue Max costs around £1,645 for the unit only. With installation, expect to pay around £2,145 – £2,645.

This is definitely a premium option. However, you’re getting excellent quality from an established UK manufacturer.

We especially like that the boiler’s controls and display are user-friendly and easy to interpret. This is important if you worry about maintaining your boiler effectively.

4. ATAG i40C

ATAG is a renowned Dutch company supplying heating solutions to the UK. Although it’s not as well known as Ideal or Worcester Bosch, don’t let that put you off.

The ATAG i40C is part of its high-quality combi range featuring exceptionally high-efficiency ratings and ultra-long warranties.

Key specs:

• Efficiency: 94% A-rated ErP
• Fuel type: Gas
• Dimensions: 700 (h) x 440 (w) x 355 (d) 
• Hot-water flow rate: 16.2 litres per minute
• Warranty: 10 years standard (extendable up to 18 years)

Top features include:

• Built-in weather compensator to maximize efficiency
• Wifi enabled and controllable via the ATAG ONE smartphone app
• ATAG iCon stainless steel heat exchanger (with a lifetime guarantee)
• LCD easy-read display
• Built-in frost protection
• Bottom-up modulation for quiet operation

Price: The ATAG 140C comes in at around £1,500 for the unit alone and costs about £2,000 –  £2,500 installed.

This is a great boiler for large homes with higher hot water and heating demands. Its robust and high-quality features mean it’s a unit that will stay with you for the long term.

It’s also a perfect option for those who appreciate a long warranty. 10 years is standard, but it can be extended to an incredible 18 years. That’s a lot of peace of mind!

5. Navien NCB

Navien is a relatively new player in the UK market and has been supplying boilers to homeowners since 2014. 

The brand is noted for its affordable prices. While it’s cheaper than other boiler manufacturers, it still provides high-quality and reliable units that will keep your home warm and comfortable.

Key specs:

• Efficiency: 94% A-rated ErP or up to 98% with Smart Plus
• Fuel type: Gas and LPG
• Dimensions: 695 (h) x 440 (w) x 408 (d) 
• Hot-water flow rate: 16.9 litres per minute
• Warranty: 7 years

Top features include:

• Extended venting up to 20m 
• Smartphone compatible and wifi enabled for remote heating control
• IPX4 rating for water leak prevention
• Smart weather forecasting and geofencing for efficiency savings
• Smart Plus control pack included
• Stainless steel heat exchanger

Price: The Navien NCB costs £914 for the unit only and between £1,414 – £1,914 installed.

The price of the Navien NCB is very attractive and this is our top recommendation for budget shoppers. We also can’t ignore the whopping efficiency rating of 98% when used with its Smart Plus control pack. 

So, not only do you save money on the cost of the boiler, but you will save on your energy bills, too.

How To Choose The Best 40kW Combi Boiler

When choosing a 40kW combi boiler, there are a number of things to consider.

Efficiency

Energy efficiency is the top factor when looking to reduce your energy bills and lower carbon emissions. 

There are three areas to look at when considering energy efficiency:

• ErP (Energy-related Products) rating: Aim for an A-rated boiler with at least 90% efficiency.
• Condensing technology: Modern condensing boilers recover heat that would otherwise be lost.
• Modulation ratio: Look for a high modulation ratio of 10:1. This improves efficiency by adjusting boiler output to match demand.

Size of home 

A 40kW combi boiler is best suited for:

• Large detached or semi-detached homes with 3-5 bedrooms
• Multiple bathrooms (2+ showers)

A high kW boiler ensures you get continuous and strong water pressure when multiple taps or showers are in use. Find out more here about showers and combi boilers.

If your home is smaller, a 30kW or 35kW combi boiler may be a better choice to avoid excessive energy consumption.

Warranty

A long warranty indicates confidence in the boiler’s durability. Therefore, you need to consider:

• The minimum warranty period. We recommend choosing a boiler with a warranty of at least 7 years, though many premium models offer 10-12 years.
• Availability of parts. Some brands have better UK support networks for easier repairs. For instance, Worcester Bosch is manufactured in the UK and has an excellent support network.

Boiler size and installation space

Check the boiler’s dimensions to see if it fits in the desired space. Also, ensure that the existing pipework and flue placement align with the new boiler’s requirements.

If it doesn’t, you may have to consider moving its location, which will undoubtedly result in increased installation costs.

Hot water flow rate

A 40kW combi boiler is capable of delivering 14-16 litres per minute (LPM) of hot water.

Does this meet your household’s needs? Especially if multiple bathrooms are in use simultaneously.

Fuel type and compatibility

All 40kW combi boilers are mains gas fitted. However, some models can be converted to accommodate LPG.

You may want to consider a boiler compatible with hydrogen gas mixes (like the Worcester Bosch Greenstar 8000) to future-proof your investment.

Check out this article for a good alternative to gas boilers. For instance, if you don’t want to use gas, you can consider the oil boiler. 

Smart controls and features

Smart controls provide you with convenience and the ability to control your home’s heating remotely. Look for models that include wifi connectivity and smartphone apps.

Additionally, many combi boilers can automatically adjust heating based on outdoor temperature to avoid freezing.

Cost and installation

Choose a boiler that fits your budget but also provides high-quality features so it lasts the duration.

Expect to pay around £1,500 – £3,000 for a 40kW combi boiler from a reliable brand. Installation costs range from £500 – £1,500, depending on complexity.

Noise levels

If the boiler is installed near bedrooms, look for models with a low decibel rating (<50 dB) so you won’t be disturbed by the operating noises.

Frequently Asked Questions

How does a combi boiler work?

Combi boilers heat your home instantly and provide hot water on demand.

Combi boilers are connected directly to the mains water supply, therefore, when you turn on a hot tap, the combi heats water from the mains and then sends it directly to the tap. This eliminates the need for water storage tanks.

For larger homes with more than one bathroom, you need a combi boiler that has high domestic hot-water output ratings – typically 40kw or higher.

Want a combi boiler with the benefits of a system boiler? Check out the best storage combi boilers that have a built-in hot water cylinder.

You can also check out a list of the best combi boilers available right now.

How much do 40kW combi boilers cost?

The new combi boiler cost is around £1,500 for the boiler itself, with installation adding an extra £500 to £1,000.

All heating engineers have their own installation prices. They can vary depending on the boiler type, complexity, and location. Boiler installation in London is the most expensive.

Comparing multiple quotes is a great way to get the best deal for your combi boiler install. 

Read more about boiler replacement in the UK here.

Are storage combi boilers any good?

Storage combi boilers are a sort of hybrid between system and combi boilers. 

They combine the best of both as they have the instant hot water capabilities of a combi boiler, but also have a built-in hot water tank like a system boiler. 

This means they can deliver hot water to multiple taps. For an example of a storage combi boiler, check out our Viessmann Vitodens 111-w combi boiler review.

What is the most reliable combi boiler in the UK?

The most reliable combi boilers in the UK are produced by Viessmann, Ideal, and Worcester Bosch. They all stand out for their quality, reliability, and innovative technology.  

When choosing between the brands, it comes down to your preference for the features they offer. Therefore, it is recommended to compare boiler brands to find the right fit for you.

What is the most economical combi boiler in the UK?

One of the most economical boilers in the UK is the Baxi 400 Combi 2. 

It costs around £700 for the unit and is available in outputs of 24kW and 30kW.

For an economical boiler with a larger output (40kW), the Navien NCB is a great choice, costing only £914.

What is the number one boiler in the UK?

The Worcester Bosch Greenstar 8000 is widely considered the number one boiler in the UK. It stands out for its advanced features, excellent efficiency, and quality. It’s also regarded for its extra-long 12-year warranty.

This boiler is available in a range of outputs and costs around £1,500 for the unit plus installation costs.

Final Thoughts

Choosing the best 40kW combi boiler is an important decision for homeowners who need a powerful and efficient heating system. 

We hope you will find the right boiler for your needs from the list in this article. Whether you go for Worcester Bosch, Ideal, or another brand, you can be assured of the quality and reliability.

Make sure you consider various factors such as your home size, warranty period, cost, etc., because this will enable you to select the perfect model.
For more information about combi boilers and selecting one for your home, we welcome you to get in touch with the friendly Boiler Central team.