Best gas and oil 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.

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

Gas boiler brands rated

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.  

Electric boilers – check out our brand new results for 2025 on brands including Ferroli, Heatraie Saida and Viessmann.

Small boiler brands

Big names such as Baxi, Vaillant and Worcester-Bosch dominate the boiler market, boasting thousands of customers. But there are plenty of smaller, lesser-known  boiler brands, including the likes of Biasi, Ferroli and Intergas.

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. 

Oil boiler brands rated

Not enough people in either our 2024 or 2025 boiler surveys owned oil boilers for us to score the brands on their feedback. The number of households with oil boilers has declined in recent years as other methods of heating, such as heat pumps and electric boilers, become more widespread.

However, you can read the results of our 2023 boiler survey of 881 owners and 198 boiler engineers below. 

Firebird and Worcester Bosch earned customer scores of five stars and three stars respectively, showing that their owners are very pleased. But do boiler engineers agree with them and how reliable will the boilers prove once installed?

Firebird oil boiler engineer and reliability scores

Owners rate Firebird oil boilers highly, but do the engineers that install, service and repair them agree? Plus, how likely are they to need a repair?

The Which? boiler survey reveals all you need to know about this popular brand. 

Log in or sign up to Which? to see the full results and find which are the best.

Worcester Bosch oil boiler engineer and reliability scores

Owners of Worcester Bosch oil boilers rate them highly, but what do the heating engineers that service them think of how well they're built, how easy they are to repair and how long they last?

Log in or sign up to Which? to see the full results and find which are the best.

Or, if you're looking for a gas boiler, Which? members can find pricing information and our experts' comments in our Worcester Bosch gas boilers review.

The cost of a new boiler will also include system cleaning and labour costs. 

Read our guide how much does a new boiler cost? to find out how much you should expect to spend.

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. 

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.