James Elston

Published April 9, 2024

Choosing the best 30kW combi boiler is vital for homeowners as it can significantly impact the efficiency of their central heating systems.

The size and features are equally important, and energy efficiency, performance, and reliability should be considered. We encourage you to read about combi boilers to help you choose the right one.

This comprehensive guide from Eco Happy provides expert recommendations and insightful tips on the best 30kW combi boilers for 2024.


Affordable 30kW Combi Boilers

In the UK, boilers that cost around £815 to £1,550 for the unit itself fall into the affordable category. When installation costs are included, the affordable price range is around £1,500 to £3,000. 

These are the most affordable 30kW combi boilers on the market today:

1. Worcester Bosch Greenstar 2000 30kW – Best overall

The Worcester Greenstar 2000 is an affordable combi boiler from the Worcester Bosch range.


  • Efficiency rating: 93%
  • Band rating: A-rated
  • Flow rate: 12.3 litres per minute (L/min)
  • Warranty: 7 years
  • Hydrogen-blend-ready: Yes
  • Price: From £955
  • Total cost, including installation: £1,690 – £2,190

The Greenstar 2000 is designed to fit in smaller homes with 2-3 bedrooms. The compact design makes it ideal for kitchen or airing cupboards. The low noise level is one of its best features, which makes it an unobtrusive addition to any home.


Key features include an A-rating for energy efficiency and 93% heat and hot water efficiency, ensuring the model is eco-friendly and cost-effective. The Quick Tap water-saving feature is an incredible addition, contributing to water conservation.

As well as the warranty on the entire unit, there is also a 10-year guarantee on the primary heat exchanger. This is an excellent addition as aluminium heat exchangers can sometimes be vulnerable to rust and corrosion. 

2. Viessmann 050-W 30kW Combi Boiler – Most versatile combi boiler

This Viessmann combi boiler model is a fantastic option for medium-sized homes with a versatile central heating system.


  • Efficiency rating: 97%
  • Band rating: A-rated
  • Flow rate: 12.2 L/min
  • Warranty: 10 years on parts and labour
  • Hydrogen-blend-ready: Yes
  • Price: From £1,100
  • Total cost, including installation: From £1,900 – £3,500

The Viessmann 050-W model is compatible with LPG and is certified to run on a 20% hydrogen blend. The compact size and stainless steel heat exchanger contribute to its longevity and durability.

With an impressive 97% efficiency rating and low CO2 emissions, the Viessmann 050-W focuses on both environmental friendliness and cost savings.


Key features include a digital LCD interface to improve user-friendliness and a WiFi thermostat. The brand only provides extended warranties from 10 to 12 years if a Viesmann-certified technician installs the combi boiler. Overall, this combi boiler promises durability and peace of mind.

3. Ideal Logic Plus C30 30kW – Good value for a great price

This combi boiler from Ideal is an excellent choice for mid-range properties. It functions as a central heating boiler and water heater.


  • Efficiency rating: 94%
  • Band rating: A-rated
  • Flow rate: 12.4 L/min
  • Warranty: 7 years
  • Hydrogen-blend-ready: Yes
  • Price: From £1,500
  • Total cost, including installation: From £1,645 – £2,145


With an A-rated efficiency of 94% and a 7-year warranty, the Ideal Logic Plus C30 combi boiler provides peace of mind for homeowners. It has a backlit digital display, an integral filling loop, and a built-in automatic bypass valve.

One of the most noteworthy features is the outdoor sensor. This sensor can optimise the water temperature based on outdoor conditions, significantly improving the boiler’s efficiency.

While the standard Logic combi boiler model has a 2-year warranty, the Logic Plus C30 provides an extended coverage period, making it a more reliable choice for homeowners looking for a durable solution.

4. Ariston Clas One 30kW – Best for small homes

The Ariston Clas One offers a quiet, compact heating and water system, ideal for smaller spaces.


  • Efficiency rating: 90%
  • Band rating: A-rated
  • Flow rate: 14.5 L/min
  • Warranty: 8 years
  • Hydrogen-blend-ready: Yes
  • Price: From £1,650
  • Total cost, including installation: From £1,650 – £2,150

These combi boilers are compatible with solar and smart thermostats, including the Ariston Net system, for improved control options. This compact boiler is highly reliable and has various heating outputs, ensuring optimum performance.


A few standout features are the backlit display that is exceptionally easy to use. The Ariston Clas One has three temperature zones to control the heat output of the radiators and the underfloor heating and can meet your hot water needs. Overall, this incredible combi boiler is perfect for households looking for a versatile heating solution.

5. Baxi 830 30kW – Best all-rounder

The Baxi 830 Combi Gas Boiler is suitable for homeowners looking for a no-fuss heating solution.


  • Efficiency rating: 93%
  • Band rating: A-rated
  • Flow rate: 12.2 L/min
  • Warranty: 10 years
  • Hydrogen-blend-ready: Yes
  • Price: From £1,900
  • Total cost, including installation: From £1,755 – £2,255

With its ability to provide both heating and on-demand hot water, there’s no need for a cylinder or water tank. Additionally, the Baxi 830 boasts an efficiency rating of up to 93%.


One of the standout features is its user interface and wall-mounted design. Features like the Easy Fill filling loop and the Adey Magnaclean Micro 2 magnetic system filter make it even more attractive. This ensures easy maintenance and protection against any system clogs.

This 30kW combi boiler offers compatibility with Baxi uSense and the In Flue Outdoor Sensor, adding an energy-saving dimension to an efficient heating system.

6. Ideal Logic Max 30kW – Best for larger households

The Ideal Logic Max 30kW combi boiler is the best boiler for large houses with 15 to 20 radiators.


  • Efficiency rating: 89%
  • Band rating: A-rated
  • Flow rate: 12.4L/min
  • Warranty: 10 years
  • Hydrogen-blend-ready: Yes
  • Price: From £1,526
  • Total cost, including installation: From £1,826 – £2,326


The Ideal Logic Max 30kW boiler is designed to meet demands for energy-efficient heating solutions. It offers WiFi connectivity and can be easily integrated with smart thermostats. With an energy efficiency rating of 94%, it provides heating while keeping energy consumption in check. This boiler has an outdoor sensor that detects the temperature around your home and can adjust the indoor temperature accordingly.  

It has also been awarded the Quiet Mark certification, which means the boiler operates quietly. In addition to its compatibility with Ideal Controls and a built-in automatic bypass valve, it is backed by years of warranty coverage for parts and labour.

7. Vaillant ecoTEC Pro 30kW – Best for mid-sized homes

The Vaillant ecoTEC Pro 30kW Combi Boiler is a reliable heating solution designed to suit homes with 1 bathroom and 3 bedrooms.


  • Efficiency rating: 93%
  • Band rating: A-rated
  • Flow rate: 12.3 L/min
  • Warranty: 10 years
  • Hydrogen-blend-ready: Yes
  • Price: From £1,211
  • Total cost, including installation: From £800 – £2,600


One noteworthy aspect of this boiler is its controls, which go beyond hot water temperature controls and timers. Equipped with an integrated display, you can easily:

  • Monitor pressure levels
  • Access fault code information
  • Keep track of the hot water temperature

Control options include the vSMART thermostat, which provides users with flexible levels of control based on their preferences. Another key feature is the stainless steel heat exchanger that can handle high flow rates and is corrosion-resistant.

Finally, the Quiet Mark certification makes this 30kW combi boiler one of the most silent (and visually appealing) boilers on the market.

8. Viessmann 200-W 30kW – Best tech capabilities

This combi boiler is a technological marvel in the domestic gas boiler market.


  • Efficiency rating: 94%
  • Band rating: A-rated
  • Flow rate: 12.3 L/min
  • Warranty: 10 years
  • Hydrogen-blend-ready: Yes
  • Price: From £1,550
  • Total cost, including installation: From £1,500 – £3,500


The Viessmann Vitodens 5-inch touchscreen display makes it easy to see information like the temperature, boiler status, and energy input.

With the “energy cockpit” feature, you can keep track of your energy usage, further enhancing the boiler’s efficiency over time. This modern boiler also has WiFi capabilities. It is compatible with a smartphone or tablet, allowing remote control through a mobile app.

Overall, its impressive energy efficiency, smart integrations, and user-friendly touchscreen make it an excellent choice for heating solutions.

9. Vaillant ecoTEC Plus 838 30kW – Best flow rate

The Vaillant ecoTEC Plus 838 Combi Boiler combines performance and convenience. It provides hot water in just 5 seconds and is ideal for small to medium-sized homes where space saving is essential.


  • Efficiency rating: 93%
  • Band rating: A-rated
  • Flow rate: 15.9 L/min
  • Warranty: 5 years
  • Hydrogen-blend-ready: Yes
  • Price: From £1,408
  • Total cost, including installation: From £2,208 – £2,708


The combi boiler features stainless steel heat exchangers, a modulating low NOx burner and fan system, and a wide modulation range of up to 1:6, ensuring exceptional performance. Like other Vaillant brand boilers, you can get an extended warranty of 7-10 years if a Vaillant-certified installer is used.

Premium 30kW Combi Boilers

Premium combi boilers are often more expensive but feature even more advanced technology, including modulating burners, smart controls, and the latest stainless steel heat exchangers. These innovations also contribute to higher energy efficiency, resulting in lower energy costs.

1. Viessmann Vitodens 100-W 30kW – Best ErP rating

The Viessmann Vitodens 100-W is one of the few combi boilers that is suitable for a medium-sized home with 10-15 radiators.


  • Efficiency rating: 98%
  • Band rating: A-rated
  • Flow rate: 15.6 L/min
  • Warranty: 5 years (can be extended to 12 years)
  • Hydrogen-blend-ready: Yes
  • Price: From £2,230 – £2,730
  • Total cost, including installation: From £2,230.00 – £2,730.00


The Viessmann Vitodens 100-W combi boiler includes a flame lift detection system, two-stage frost protection, and Quiet Mark accreditation. It is also compatible with the auroTHERM air-to-water heat pump system, making it a versatile solution for homeowners who value reliability.

One notable feature of this system boiler is its Lambda Pro technology. This technology ensures adjustment of the gas valve to maintain efficiency and burn rate.

In addition to the LCD touchscreen display, the boiler includes integrated WiFi, allowing users to access control and diagnostic capabilities remotely. This means you can seek Viessmann’s support for fault diagnosis without on-site assistance. 

Additionally, the display provides information on failed components, potentially reducing costs associated with fault diagnosis.

2. Worcester Bosch Greenstar 4000 30kW – Best for low water pressure Areas

The Worcester Bosch Greenstar 4000 is a good choice for medium-sized homes with warranties lasting up to 12 years.


  • Efficiency rating: 94%
  • Band rating: A-rated
  • Flow rate: 12.3 L/min
  • Warranty: 10 years
  • Hydrogen-blend-ready: Yes
  • Price: From £2,265 – £3,125
  • Total cost, including installation: From £2,000 – £2,500


This boiler’s high ErP rating of 94% demonstrates its commitment to energy efficiency and modern living, especially with its compatibility with thermostats and mobile devices.

What sets it apart is the Quick Tap water-saving technology, making it more appealing for those in low water pressure areas. Features include WiFi connectivity and Bosch’s EasyControl thermostat.

The Greenstar 4000 offers a range of accessories, including the EasyControl RF Key, Compact remote PRV kit, and system filters.

3. Worcester Bosch Greenstar 8000 Style 30kW – Best warranty

This combi boiler carries on the brand’s efficiency and stylish design tradition. As a replacement for the Greenstar CDi model, it boasts an impressive ErP efficiency rating of 94%, contributing to reduced carbon emissions and lower heating costs.


  • Efficiency rating: 94%
  • Band rating: A-rated
  • Flow rate: 12.3L/min
  • Warranty: Up to 12 years
  • Hydrogen-blend-ready: Yes
  • Price: From £2,845
  • Total cost, including installation: From £2,100.00 – £2,600.00


These energy-efficient combi boilers meet the demands of busy families with high water demands. This wall-mount boiler is compact in design and can easily fit into kitchen cupboards.

Its smart filling system ensures that the pressure is maintained optimally. The combi boiler also seamlessly integrates with wireless control technology such as the Bosch EasyControl thermostat, offering users an efficient experience.

With its display and advanced features, the Greenstar 8000 Style perfectly represents Worcester Bosch’s dedication to delivering technologically advanced heating solutions.

How We Chose The Best 30kW Combi Boilers

Here are the methods we used to determine the best 30kW combi boilers currently on the market.

Customer reviews

We thoroughly analysed customer reviews of 30kW boilers on review sites like Trustpilot. We looked out for boilers with four or five-star reviews, and we also searched for keywords that matched our criteria for a good boiler such as “energy efficiency” and “great warranty”. 

Customer reviews are a great source of knowledge about boilers as they come from people who have real experience using the products. They also tend to be very honest about the pros and cons, which gives us a rounded picture of the boiler’s strengths and weaknesses. 

Independent testing bodies 

Another one of our go-to sources are independent testing bodies like the Energy Saving Trust, BEAMA (British Electrical and Allied Manufacturers Association), and Which?. These objective bodies carry out tests on boilers and provide impartial results and reviews. 

They use standardised procedures that analyse important criteria like efficiency, power, and reliability. By assessing these test results, we can gain in-depth knowledge of how well a boiler performs and decide if it’s good enough to make our list.

Why Choose A 30kW Combi Boiler?

For combi boilers, the kilowatt (kW) rating mainly determines the amount of hot water it can deliver.

If you choose a combi boiler that’s too small, it may be unable to keep up with your heat and hot water demands. On the other hand, a boiler that’s too large will be less efficient and more expensive to run.

If you’re asking yourself “What size boiler do I need?” and “Will a 30kW combi boiler be sufficient?“, you need to take the following into account:

  • Your property’s size
  • The insulation level
  • How much heating your home requires
  • Efficiency and cost

When is a 30kW combi boiler the ideal choice?

The 30kW boiler output is suitable for a medium-sized home with moderate heating requirements and 10-15 radiators. It provides warmth without wasting energy if your property has balanced heating and average hot water demands.

The Benefits of 30kW Combi Boilers

  • Sleek design: One attractive feature of 30kW combination boilers is their stylish design. Many modern boilers are small enough to be mounted on the wall if they do not need a hot water tank.
  • 30kW combi boiler cost: A 30kW boiler is a cost-effective heating solution for a 3- to 4-bedroom house. Select one that suits your heating needs and reduces energy costs rather than overspending on a larger combi boiler unit.
  • Smart technology integration: Most modern 30kW combination boilers have WiFi capabilities, allowing control through a device like your smartphone. This smart technology enables monitoring and adjustments, improving user convenience and energy management.
  • Versatile: These combi boilers are versatile and suitable for small (1-2 bedrooms) to mid-sized properties, making them a flexible option for heating your home.

Top Features To Look For

Combi boilers should include the following key features:

Energy efficiency ratings

A boiler’s energy efficiency rating uses the letters A to G, accompanied by a percentage. For instance, a boiler with an energy efficiency rating of 90% means that 90% of the fuel’s energy is used to produce heat while the remaining 10% is wasted. When a boiler has higher efficiency ratings, it shows that it is better at converting fuel into heat.

The ratings can be found on a sticker on modern combi boilers or the boiler pack. Alternatively, check the boiler efficiency database to find the following ratings:

  • A – 90% and over
  • B – 86-90%
  • C – 82-86%
  • D – 78-82%
  • E – 74-78%
  • F – 70-74%
  • G – below 70%

Flow rate

Another crucial factor to consider is the flow rate of the new combi boiler, which measures how much water it can deliver per minute. Choose a boiler with a flow rate that matches the hot water needs of your household. 

For example, the flow rate for a 3-4 bedroom house should be 12-15 litres per minute. Flow rates are typically measured in litres per minute (L/min) or gallons per minute (GPM).

Fuel type

Consider the fuel type when selecting a boiler – options include gas, propane, and oil. Choose the most convenient and cost-effective fuel source based on your location. However, most modern combi boilers offer the flexibility to transition to hydrogen.

A hydrogen-blend-ready combi boiler is a gas-fired boiler that can burn 80% natural gas and 20% hydrogen and is readily available. Although no 100% hydrogen-ready boilers are on the market yet, hydrogen-blend-ready boilers can adapt to hydrogen fuel quickly.

Condensing technology

A condensing combi boiler is recommended as they are more energy efficient. Condensing boilers use heat from flue gases that would otherwise be wasted. This can result in long-term energy savings.

Compatibility with smart thermostats

Look for compatibility with thermostats when choosing a combi boiler. Most modern combi boilers allow for control and programming through smartphone apps and are compatible with some of the best smart thermostats on the market.


Take a moment to check the warranty provided by the manufacturer. An extended warranty period can offer peace of mind. This will indicate that the manufacturer is confident in the durability and reliability of their products.

Comparing The Best 30kW Combi Boilers: What Sets Our Top Picks Apart 

  1. Viessmann Vitodens 100-W 30kW: Erp: 98%; Warranty: 5 years (12 years extended); Price: £2,230
  2. Viessmann 050-W 30kW combi boiler: ErP: 97%; Warranty: 10 years; Price: From £1,100
  3. Worcester Bosch Greenstar 8000 Style 30kW: ErP: 94%; Warranty: 12 years; Price: From £2,845
  4. Worcester Bosch Greenstar 4000 30kW: ErP 94%; Warranty 10 years; Price: From £2,265 – £3,125
  5. Viessmann 200-W 30kW: ErP: 94%; Warranty: 10 years; Price: From £1,550
  6. Worcester Bosch Greenstar 2000 30kW: ErP: 93%; Warranty: 7 years; Price: From £955
  7. Ideal Logic Plus C30 30kW: ErP: 94%; Warranty 7 years; Price: From £1,500
  8. Baxi 830 30kW: ErP: 93%; Warranty 10 years; Price: From £1,900
  9. Vaillant ecoTEC Pro 30kW: ErP 93%; Warranty 10 years; Price: From £1,211
  10. Vaillant ecoTEC Plus 838 30kW: ErP: 93%; Warranty: 5 years (7-10 year extended); Price: From £1,408
  11. Ariston Clas One 30kW: ErP: 90%; Warranty: 8 years; Price: From £1,650
  12. Ideal Logic Max 30kW: ErP: 89%; Warranty: 10 years; Price: From £1,526

Installation Process And Costs

A Gas Safe engineer must install combi boilers. Not only is it a legal requirement, but it is a safety issue as well. Attempting DIY installations can lead to gas leaks or water damage. Trained installers adhere to safety protocols to ensure that gas appliances are correctly connected, ventilated, and operated safely, reducing potential hazards.

On average, it costs around £1,500 – £3,000 to have a 30kW combi boiler installed by an engineer. The cost can vary greatly depending on the specific requirements of your property and the complexity of the installation. 

How Often Should You Service A 30kW Combi Boiler?

Maintaining your combi boiler is always cheaper than replacing it. A Gas Safe registered engineer should carry out the maintenance. This should be done annually to ensure your combi boiler operates smoothly. Skipping a service could void the warranty on your boiler. 

A typical combi boiler service takes around one hour to complete. Once done, you will receive a service report or certificate containing details of the repair or checks.

Landlords should also take note of the boilers installed in their rental properties. It is a legal requirement for a landlord to receive a CP12 certificate, which is a safety certificate issued by Gas Safe engineers after inspection. This certificate must be renewed annually, and properties can’t be let without it.


How long does a combi boiler last for?

As long as it’s properly maintained and serviced, your combi boiler should last for around 15 years. However, the longevity of a combi boiler can be affected by several factors such as its usage levels, the quality of its installation, and the quality of the boiler itself. 

What are the disadvantages of a combi boiler?

The most common complaint from users is the decline in water pressure. Combi boilers draw directly from the main supply, causing water pressure to drop when multiple appliances use hot water at the same time.

What is better than a combi boiler?

Conventional boilers are a great alternative to combi boilers. Many households opt for unvented condensing boilers since they offer main-pressure water and work well for both small and large families.

Final Thoughts

Choosing the best 30kW combi boiler is essential for homeowners who want to optimise their heating systems and reduce overall energy usage. Both the Vaillant ecoTEC Pro and Ideal Logic Max are options that meet this requirement. However, when it comes to selecting the “one”, it ultimately depends on preferences and specific needs.

The Viessmann Vitodens 100-W and Worcester Bosch Greenstar 4000 are also worth considering, as these powerful combi boilers offer a combination of features, energy efficiency and extended warranty coverage. Contact Eco Happy and we’ll provide you with a quote on the best 30kW combi boiler for your home.

James Elston

Boiler Expert

James Elston is the top boiler replacement and heating expert at Eco Happy. He has over 20 years of experience in the industry, focusing on Gas Safe boiler installations and offering home-heating and energy-saving solutions to homeowners across the UK. From sourcing the most energy-efficient combi boiler to providing specialist heating advice, James ensures that Eco Happy maintains the highest standards and best customer service.

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