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What heating engineers really think of your boiler

Trusted heating engineers share their views on boiler brands including Baxi, Biasi, Vaillant and Worcester Bosch

Unlike buying a TV, where you can walk into the shop and pick one up off the shelf, the boiler industry relies on heating engineers recommending, sourcing and installing them. So it can be pot luck in terms of the brand you’re dealt and the price you pay, especially because engineers are incentivised by certain manufacturers. 

That’s why we asked 171 expert heating engineers to rate all the gas boiler brands available to buy in the UK – and our special formula means we’ve removed any bias from their responses.

They told us about everything from the build quality of each boiler brand and whether they would recommend it, to how easy it is to get hold of spare parts, how easy a common fault is to fix and how easy each brand is to service.

The results reveal a few clear favourites, and some manufacturers engineers think you should avoid like the plague.


Head here if you just want to know which are the best boiler brands. Or if you need a new system this winter, here’s everything you need to know before you buy a new boiler.


Availability of boiler parts and spares

If your boiler breaks down in the depths of winter and needs a new part, you’ll want to know you own a brand that heating engineers can easily get parts for, so you’re spared an an extra day or two of freezing showers and an uncomfortably cold house.

We asked each heating engineer how easy or difficult it is to get hold of parts and spares for each brand, and you can see the results below.

Many of the biggest boiler brands in the UK have established networks to get parts to you quickly. But you might struggle with smaller brands such as ATAG, Ferroli, Keston and Johnson & Starley.

Ease of fixing a boiler

We also asked heating engineers how easy they find it to fix a common fault. The fault in this instance was replacing a boiler’s domestic hot water heat exchanger.

Some manufacturers make this fault easier to repair than others, depending on where the part is located in the boiler.

Vaillant is the easiest boiler to fix, but Worcester Bosch, one of the biggest boiler brands on the market, languishes in the middle of the pack with more saying fixing a fault is difficult than easy.

Best boiler brands according to heating engineers

As well as answering the questions above, we also asked each engineer what they think of the build quality of each brand.

Almost nine in ten (86%) thought the build quality of the brand that came bottom on this measure was poor. That’s compared with 83% of engineers who thought the build quality of the highest-ranked brand was good.

To find out which brands our expert engineers think are built to last, and the ones they would recommend, look at our best boiler brands page.

The boiler brands rated in our 2019 survey

List of boiler brands in the 2019 survey

Our research

We sent Which? Trusted Traders an online survey in May and June 2019, and 171 completed the survey.

Heating engineers are often incentivised to install one brand over others, so in order to remove bias from the results we omitted responses from engineers who were either incentivised to install, or accredited with the brand.

So, for example, when you log in to our boiler reviews, and see a five-star recommendation for a brand, you’ll know that really is a strong recommendation as the engineers aren’t incentivised to give a positive review..

For our boiler reviews we combine the results from our engineers’ survey with the reliability and customer score ratings from our general public survey of people who have bought a boiler in the past six years.

The difference in reliability between brands is astounding, with the least reliable three times as likely to develop a fault as the most reliable brand.

If the worst happens to you this winter and you need to replace your boiler, make sure you buy one that’s reliable and liked by engineers and customers alike, by picking one of our Best Buy boiler brands.

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