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How to buy the best boiler

By Matthew Knight

Expert advice on how to find the best boiler for your home. From picking the right size to the ideal type, we'll help you buy a boiler that won't let you down.

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A new boiler is likely to be one of the most expensive household purchases you'll make. So it's important to choose the right boiler from the right brand at the right price. Watch our video above to get top tips on buying the best boiler for you. 

The silver lining is replacing an old non-condensing boiler with a modern condensing system can improve your boiler's efficiency by more than 30%, saving you a substantial amount on your annual heating bill.

You can use our choosing tool below to help you select the best type of boiler for your home – whether it's a combi, heat-only or system boiler. 

Select a boiler type, then click the green circles to find out more.

We only award Best Buy boilers to the brands that are reliable, well loved by people who own them and are respected by heating engineers. 

Use our independent reviews to find out which new models we recommend as the best boilers

Gas boiler, oil or LPG boiler?

Most UK households have a gas heating system equipped with a gas boiler. But if you're one of the the estimated 4.3m households not connected to the UK's gas network, there are alternatives. 

These include fitting an oil boiler, liquid petroleum gas or LPG boiler, or a wood-burning stove fitted with a back boiler. 

See our oil boilers page for more information. If you want to know more about heating oil costs, go to our heating oil guide

Types of gas boiler

If you have a gas heating system with a gas boiler, you need to choose between:

  • Combi (combination) boiler, which provides heat for your radiators and domestic hot water on demand.
  • Heat-only (conventional) boiler. This will have a hot water storage cylinder and also a large cold water feed tank, usually in the loft.
  • System boiler This is much like a heat-only boiler, but it doesn't require the extra space you need for a cold water storage tank.

For more information, make sure you take a look at our guide to 5 things you need to know before you buy a boiler.

You should also ask your heating engineer for their opinion.

Boiler efficiency 

If you have gas central heating, your boiler will account for around 60% of your home's CO2 emissions*. This makes your choice of boiler a key priority if you're looking to cut your energy bills and carbon footprint.

Boiler efficiency is an integral part of our independent boiler reviews. You can filter our boiler reviews by efficiency rating, but the reality is that there's not much disparity when it comes to modern condensing boilers – most will be around 90% efficient. 

Replacing an old-fashioned non-condensing boiler with a modern condensing system can improve efficiency by as much as a third, and will save you a significant amount on your energy bills. However, in terms of choosing between new condensing boilers, there is little difference in how efficiently they produce hot water. The key to getting the most efficient new boiler is in picking the right type and size boiler for your home. 

*Source: Energy Saving Trust.

Getting the right size new boiler

Boiler sizing includes two things:  

  • The heating and hot water capabilities of the boiler  
  • The physical size of your boiler and whether it will fit in the space you have it destined for. 

The correct heating size of the boiler will be something unique to you and your home, as it depends on things such as how many bathrooms you have and how many people you live with. This is something your heating engineer can help you with, and they will be key to making sure you achieve your hot water and heating requirements. 

In our boiler reviews, we display each boiler's hot water and heating capabilities, and give an indication as to what type of home it's suitable for. We also display the boiler's measurements, so that you can figure out if it will fit in the space you have for it.  

It's always good practice to ask your heating engineer what size boiler they think best fits your requirements.

Buying a reliable boiler

We know that when it comes to buying a new boiler, reliability and dependability are by far the most important factors that will influence which boiler you'll buy. So we go to great lengths each year to separate the good from the bad brands in terms of reliability. 

We survey more than 10,000 boiler owners each year, so that we can tell you with great confidence which boiler brands will keep you warm all winter, and which might leave you with cold showers and freezing-cold radiators. 

The graph below shows how many boilers remained fault-free – as you can see, there's a big difference between the best and worst brands. After six years, you're almost twice as likely to have experienced a fault with the worst brand than the best. 

With the average cost of a single repair hovering around £210, you'll want to know which are the best and worst boiler brands before you buy that new boiler. 

The best boiler brands

Become a Which? member to unlock the tables below and discover the best boiler brands.

Best boiler brand overall

Reviewed -

This brands boilers have topped thecharts in our customer and engineers survey over the past few years. Its combi boilers are reliable and loved by those wh oown them and the engineers who fit and service them.

Most reliable boiler brand

Reviewed -

This brand of boilers has a peerless reliability record. It's also loved by its customers and heating engineers think its build quality is top notch.

Engineers' favourite boiler brand

Reviewed -

This brand is completely adored by expert heating engineers. They rave about its build quality and award it 5 stars on every measure in our Which? Trusted Trader heating experts survey.

Boiler installation 

Don't attempt to install a replacement boiler yourself - leave it to the professionals. You can find a qualified heating engineer on the Gas Safe Register (the gas registration scheme previously run by Corgi), or use Which? Trusted Traders as the best place to start to find a local, trustworthy heating engineer for your boiler installation. 

Always get at least three quotes and make sure they include all costs, including any call-out fees. Don't be taken in by any headline discount figures – look at the total price of the boiler and labour charges.

You may find that some installation companies, including services offered through British Gas and other energy companies, will suggest a replacement boiler for you rather than allowing you to choose your preferred model. This is because many heating engineers are incentivised to install particular brands. 

It's vital you check your heating engineer's recommendation against their peers - we have this data.

So it's vital that you check your heating engineer's recommendation against the views of their peers – which is where we can help. We surveyed 179 Which? Trusted Trader heating engineers to find out what they really think of the different boiler brands on the market. You can use our research to make sure you pick the best boiler brand for your home. 

Check out the best boiler brands, then make your wishes clear to the installer from the outset.

Heating controls

Heating controls let you take charge of when, where and at what temperature your heating is operating. It’s a good way of managing your heating costs, as you can ensure that your heating is only on certain rooms at certain times. 

When you come to replace your boiler, it may be a good time to install a heating control system. Find out more with our guide to the best boiler controls.


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