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How we review combi boilers: Our methodology for testing and rating boilers

A combi boiler, short for combination boiler, is a compact unit that provides both heating and hot water directly from the mains. This type of boiler is popular due to its efficiency and compact size, making it a great choice for homeowners.

However, given the number of combi boiler alternatives available today, finding the most suitable one can seem daunting. Our expert team has meticulously assessed and ranked various boiler brands and models, evaluating their functionality, features, and price points, enabling you to make a more educated choice.

To produce accurate, objective and reliable results, we scrutinise and rate 35 specific factors. The boiler’s performance in these factors determines its overall rating and forms the cornerstone of our recommendations.

Each of the parameters we’ve tested falls within one of the following categories:

  • Performance and features
  • Provider/installer performance
  • Value for money
  • Customer experience

We calibrate the weighting of each aspect according to its relevance in identifying the optimal combi boiler. For example, we regard the boiler’s energy efficiency as more pivotal than its design appeal, so the efficiency rating will carry more weight in the final score. While we’re not suggesting that aesthetics aren’t necessary, we prioritise a combi boiler that provides an outstanding heating performance over one that merely adds to the visual appeal of a home.

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The combi boiler features we prioritise

We think the critical factors in determining a combi boiler’s quality are:

  • Energy efficiency
  • Performance and reliability
  • Features, including safety considerations
  • Durability and build quality
  • Installation process
  • Manufacturer 
  • Cost
  • Warranty
  • Customer support
  • Aesthetic appeal

Energy efficiency

An energy efficient combi boiler operates more economically, consuming less fuel to provide the same level of heat and hot water, which directly translates into lower energy bills. Over the lifespan of the boiler, these savings can be significant. They also produce less carbon dioxide (CO2) emissions. By using the fuel they consume better, energy efficient boilers have a reduced environmental footprint, which is increasingly important given global efforts to combat climate change.

Performance and reliability

When we talk about the performance of a combi boiler, we’re referring to its ability to generate heat and hot water efficiently and consistently. A high-performing boiler can quickly heat your home to your desired temperature and provide a steady hot water supply. This becomes particularly critical during winter months when heating demands are high.

Reliability refers to the boiler’s ability to perform its functions consistently over a prolonged period without breaking down. An unreliable boiler can cause significant inconveniences, potentially leaving you without heat or hot water access. Besides the discomfort, this could also incur emergency repair or replacement costs.

Our experts thoroughly check the reliability and performance of the combi boilers we review.

Features, including safety considerations

Our experts analyse every combi boiler for its features, with a particular focus on its safety considerations. 

Features such as programmable thermostats, user-friendly interfaces, and compatibility with smart home systems can enhance the boiler’s usability. Programmable thermostats, for example, enable you to set the temperature for different times of the day, allowing for optimal comfort and efficiency. A user-friendly interface makes it easier to operate the boiler and adjust settings, while smart home compatibility allows for remote control and monitoring of the heating system.

Some boilers also offer features for specific needs, such as frost protection for areas with extremely cold temperatures, or compatibility with solar panels for households aiming for renewable energy use. These features help customise the user experience, catering to specific household requirements.

Safety considerations are equally – if not more – important. Combi boilers are designed with various safety features to prevent issues such as gas leaks, overheating, or excessive pressure build-up, which can pose significant risks. Many models include the ability to detect potential gas leaks. If a leak is detected, the system will shut down automatically to prevent accidents. These safety measures are crucial to protect both the homeowner and the integrity of the heating system.

Durability and build quality

A combi boiler with a durable design and high build quality is more likely to have a longer lifespan. This not only means you won’t need to replace the boiler as often, but also that the unit will maintain optimal functionality over a longer period, providing consistent heat and hot water supply without frequent breakdowns. Longevity in a boiler’s performance brings a sense of security and reliability to homeowners.

A high build quality often indicates the components used in the boiler are more robust and resistant to wear and tear. This reduces the likelihood of mechanical or electrical failures, which can result in costly repairs or replacements. Additionally, a well-built boiler is more likely to operate efficiently, leading to energy savings in the long run.

Also, it’s important to note that poorly constructed boilers could pose risks, including gas leaks or failures in safety systems. A high-quality build ensures these systems function as intended, protecting your home and family from potential hazards.

Installation process

Some combi boilers are easier and quicker to install than others, and that can result in less labour and installation costs. It also minimises the disruption to your household routine, which can be crucial for many homeowners.

The installation process can also impact the performance and efficiency of the boiler. If a boiler requires a complex installation, there’s a higher risk of an incorrect fitting, which could compromise its operation, efficiency, and even safety. Boilers that are easier to install correctly are more likely to operate as intended and deliver optimal performance.

We research the entire installation process of every combi boiler we review.


The manufacturer of a combi boiler plays a significant role when reviewing and evaluating an appliance. Its reputation and track record can provide insights into the expected quality and reliability of the boiler. Manufacturers with a strong reputation in the market typically have stringent quality control processes, leading to products that deliver consistent performance and have fewer issues.

Committing to research and development can influence the technological advancement and efficiency of the boiler. Manufacturers investing heavily in this sector are often at the forefront of introducing innovative features and improving energy efficiency.


When considering the cost, it’s not only the upfront cost of the combi boiler that’s important but also the long-term operational expense. A cheaper boiler might seem attractive initially, but if it’s less efficient and costs more to run, the overall cost over the boiler’s lifespan could be higher. This is why it’s crucial to consider the boiler’s energy efficiency and potential maintenance costs as part of the total cost.

The cost can also reflect the quality and features of the boiler. Higher-priced boilers often incorporate advanced features, higher efficiency ratings, and better build quality. They might also come with better after-sales service or longer warranties, which can provide more value over time.


Combi boilers are complex appliances with multiple components that could potentially fail or malfunction. A warranty protects the buyer against these unforeseen issues, ensuring the manufacturer or supplier will repair or replace the faulty parts without additional cost.

Without a warranty, the homeowner could be responsible for the total cost of any repairs, which can be significant. A warranty should cover these expenses and save the owner considerable sums over time, making it an essential factor in the overall cost of owning and maintaining a combi boiler.

Our experts study and analyse every aspect of each warranty.

Customer support

Even if you are familiar with combi boilers, there may still be moments when you need assistance understanding its functioning, troubleshooting problems, or performing basic maintenance. Good customer support can provide clear, accurate guidance, saving time and stress. 

A robust customer support team reflects the manufacturer’s commitment, demonstrating confidence in the reliability and quality of its boilers. This usually means it stands by its product and is willing to help if something goes wrong. Support is also critical in the context of warranty claims. If a boiler comes with a warranty, the company should provide a seamless claims handling service, to give you the peace of mind that you are covered.

Aesthetic appeal

Combi boilers, unlike other heating systems, are often installed in visible areas of the home, such as the kitchen, hall, or utility room. Given this, a boiler with an aesthetically pleasing design can seamlessly blend into your home decor instead of sticking out as unattractive or obtrusive.

Aesthetic appeal is not just about how a combi boiler looks but also about how it’s designed for ease of use. A boiler with a user-friendly design – clearly marked dials, an intuitive display, or easy access for maintenance, for example, makes it easier for you to operate and maintain it, which adds to the overall positive experience of using the product.

You can read more about our commitment to editorial impartiality and our editorial code on our About Us page.

Katharine Allison

Energy Saving Writer

As Independent Advisor’s energy saving expert, Katharine, a keen advocate for sustainability, is an authority on solar panels, double glazing, and cutting-edge renewable energy technologies. Her dedication merges with a commitment to enlighten and steer readers toward embracing eco-friendly solutions and the latest trends in sustainability.

With over 10 years of experience, she has worked with some of the UK’s leading companies and publications, including the Federation of Master Builders, Architectural Digest, and Denon Construction. 

Katharine is particularly passionate about consumer causes and animal welfare and has art, philosophy, and psychology degrees. She lives with her sled dogs in East Sussex.