Best gas boiler brands

Every year we ask thousands of boiler owners how satisfied they are with their boiler and whether it's suffered any faults or breakdowns. 

From their responses, we work out which brands have the happiest owners and the lowest fault rates.

But this only makes up part of a boiler brand's overall review. We also ask heating engineers vetted by Which? Trusted Traders what they think of each manufacturer, including how well a brand's boilers are built, how easy they are to fix and service, and how easy it is to get spare parts. 

Some engineers are incentivised by brands to recommend their products. We filter out any responses from these engineers, and only use feedback from those with no commercial affiliation with particular brands — so you can be confident our engineer recommendations are unbiased and reliable.

We combine the engineers' scores with the brand's customer and reliability scores to reveal the best boiler brands.

We've collated the results in the tables below.

Looking for oil boilers or electric boilers instead? Head to our dedicated guides to the best oil boiler brands and the best electric boiler brands.  

Gas boiler brands rated

See which brands were ranked most highly by engineers and customers and which came top of our table overall.

Which? members should log in now to unlock the scores in the table. If you're not already a member, try Which? to unlock our boiler research and all our online reviews.  

Want an oil or electric boiler from a reliable brand? Head to our reviews of the best oil boiler brands and best electric boiler brands.

Small boiler brands

Big names such as Baxi, Vaillant and Worcester Bosch dominate the boiler market, boasting thousands of customers. Head to our individual brand review pages for each company, linked from teh table above, to see our full write-up of each one. 

There are also a handful of smaller, lesser-known boiler brands, including Biasi, Ferroli and Intergas, on the market. Our most recent boiler survey is based on boilers that have been installed in the past six years. Unfortunately, neither their owners nor the boiler engineers that have worked on models from these smaller brands rated them highly enough to feature further up in our survey. 

Biasi has the best reliability of the three smaller brands, based on our survey, although Ferroli and Intergas have average reliability.

Intergas does the best of the three, with boiler engineers being slightly more enthusiastic than owners. They said that the boilers are straightforward to service, but repairing them is sometimes tricky. The brand is reliable, so you shouldn't be troubled with too many faults, and 80% of owners are satisfied with their Intergas boiler.

Although they are reliable, the results of our latest survey show Biasi boilers aren't well liked by owners, and by engineers even less. Engineers don't have much positive to say overall, and particularly criticise build quality. Only 64% of Biasi boiler owners are satisfied with their purchase, which is in stark contrast to the best-liked boiler brand, Worcester Bosch, where 92% are satisfied.

Ferroli comes bottom of the table. Although its boilers suffer relatively few faults, boiler engineers really didn't rate them, saying the build quality is poor and that it's often tricky to find parts and to do repairs. Also, they generally aren't fans of the quality of help offered by the manufacturer to installers. The brand's customer score is low, too. 

What are the different types of boiler? Find out if a combi, heat-only or system boiler is the best type for your home.

Best boiler brands according to heating engineers

We don't just rate boiler brands for reliability and how satisfied customers are, we also gather the views of Which? Trusted Trader heating engineers. We ask them to rate boiler brands on various criteria, so you know if a brand makes boilers that are reliable, easy to fix and are well built. 

We've included their feedback in the table above, as well as in our individual brand review pages. 

How boiler scores are calculated

In May 2025, we conducted an online survey of 10,064 members of the public who bought a boiler in the past six years, and asked them about the boilers they own.  

The total score for both gas and oil boilers is based on: 

• Reliability (40%) How many boilers bought in the past six years developed a fault, factoring in time until first fault and severity. Fault had to be repaired by a trained plumber or engineer. 
• Engineer score (40%) Made up of 15% ease of sourcing parts, 15% ease of replacing common component, 15% ease of servicing, 10% manufacturer support, 20% build quality, 25% unbiased recommendations (barring incentivised engineers).
• Customer score (20%) How satisfied owners are and likelihood to recommend a brand. 

In May 2025, we also asked 225 Which? Trusted Trader heating engineers who work with boilers every day to rate the different brands. They told us their views on:

• The availability of parts and spares;
• How easy it is to fix a common fault (heat exchanger) on the brand's boilers;
• How easy it is to carry out a service on the brand's boilers;
• The build quality of a brand's boilers;
• The likelihood of them recommending the brand to a customer.

Some engineers are incentivised by brands to recommend their products; we filter out these responses.

The overall score for each brand is calculated by combining the reliability, customer and engineers' scores.

How we assess boilers - read on to find out more about how we assess boiler brands.

Which? Trusted Trader boiler installations

If you're ready to get a new boiler installed, use Which? Trusted Traders to find a reliable boiler installer near you.

For more expert advice, head to our guide to buying the best boiler.