Greenstar 4000 System
When you buy a new boiler, you'll want to be sure that it will give you years of reliable service. And, you'll want to know that it's highly recommended by heating engineers - experts who work with heating systems every single day.
Only boilers that have a good reliability record, are loved by their owners and are highly regarded by Which? Trusted Trader heating engineers can earn our Best Buy recommendation.
Read on to find out how we review boilers.
Every year, we survey thousands of members of the public about their experiences with popular boiler brands.
Our most recent survey of boiler brands was carried out in May and June 2021. We surveyed more than 8,000 members of the general public, all of whom had installed a new gas or oil boiler within the previous six years.
We analysed their responses to give each of the main boiler brands an overall customer score and a brand reliability score.
We asked members of the public about their brand of gas or oil condensing boiler, including whether they had ever needed to have it repaired, and what faults (if any) they had experienced.
The Which? reliability score is based on the proportion of boilers that have had repairs. Scores are adjusted by age, so if, from our survey, a brand's sample is made up of older boilers it isn't unfairly penalised. Doing this ensures all brands are compared on an equal basis.
We need at least 50 responses per brand to calculate a reliability score, and therefore publish an overall score for a boiler brand.
We also asked boiler owners to assess how satisfied they were, and how likely they would be to recommend their brand of gas or oil boiler (regardless of their experience of getting the boiler installed). These two questions form the basis of the Which? customer score, which is included in our .
Which? Trusted Trader heating engineers have all been through a rigorous vetting procedure to prove their expertise and the quality of their work before they qualify for Trusted Trader status.
We ask these heating engineers whether they would recommend each brand of boiler, what the build quality is like, how easy it is to fix a common fault (replacing a domestic hot water heat exchanger) and how easy it is to get hold of parts and spares.
Sometimes engineers are incentivised by manufacturers to recommend their boilers. We filter out any of these responses, so you can be sure that our heating engineer scores for each boiler brand is independent and unbiased.
This enables us to give you a unique insight into the reputation of each boiler brand amongst heating engineers, and to find out whether you're likely to get hit with a higher repair bill.
We then combine these three scores together to get a brand's overall score:
We don't send individual boilers to a test lab for the following reasons:
However, all of our boiler reviews contain the full specification, any customer views and our own expert analysis to help you find the best boiler for your home.