Best boilers 2023: Which? Best Buys and expert advice

A new boiler is likely to be one of the most expensive household purchases you'll make – usually when your current one breaks down and needs replacing.

So it's important to make sure you get one from a brand you can rely on. Read on for our advice on buying the best boiler for your home.

Already know what type you need? See our boiler reviews.

The best boiler brands

With the average price of a single repair costing about £200 (Which? boiler survey, 2022), getting a boiler from a reliable brand will cost you less to maintain over the years.

We ask owners how satisfied they are with theirs and if they would recommend it to a friend. We also survey 196 Which? Trusted Trader heating engineers to get their opinion on each brand. These are then combined to create a boiler brand's overall score.

Become a Which? member to unlock the tables below.

Tables last updated 14 September 2022.

Find out how they performed in our best gas and oil boiler brands and best combi boiler brands guide.

Video: how to buy the best boiler

When buying a new boiler, you need to consider what type you want, what size of boiler you need, whether your heating system needs anything doing to it while you're installing a new one, and which brand will be most reliable. 

Watch our video to help you decide which type is right for you.

Not sure if you need a new one? Look out for these five signs.

What type of boiler should I get?

Gas, oil and LPG

Most UK households are connected to the UK's gas network and so have a gas heating system equipped with a gas boiler. 

But for the 15% of homes not on the gas network (Energy Savings Trust, May 2021), there are alternatives such as fitting an oil boiler, liquid petroleum gas (LPG) boiler, or a wood-burning stove with a back boiler (which come with another set of environmental implications).  

Know the type of fuel you need? Read our gas boiler, oil boiler and LPG boiler reviews.

Combi, heat-only and system boilers

There are typically three different types of gas boiler to choose from: combination (combi), heat-only (also called conventional or regular) and system boilers.

• Combi boilers provide hot water on demand. Best suited for small flats or homes, with low water demands (eg one bathroom).
• Heat-only (regular) boilers require a cold water feed tank and hot water storage tank, usually installed in the loft. Best suited for larger homes with a high water demand (eg multiple bathrooms being used at the same time).
• System boilers are like regular boilers, but don't require a cold water feed tank and have more components built into the boiler body. Best suited for larger homes with poor water pressure and a high water demand.

Your heating engineer will be able to talk you through the different types and make a recommendation to suit your needs. 

Learn more about the pros and cons in our different types of boiler guide. 

Why is boiler efficiency important?

The 2021 Heat and Buildings Strategy from the Department of Business, Energy and Industrial Strategy reported 77.1 megatonnes of greenhouse gas emissions from UK homes – that's around 2,666kg per home, on average. In total, heating our homes accounts for around 17% of UK carbon emissions.

The UK is heading towards net zero carbon emissions by 2050. To achieve this, emissions will need to be reduced by 95%, to just 138kg a year per household by 2050 (Energy Savings Trust, 2021).

Since 2018, the government's Boiler Plus legislation has required that all newly installed boilers have a minimum ErP efficiency of 92%, plus time and temperature controls fitted.

But a boiler's efficiency depends on how it's working in your home. A boiler won't achieve its efficiency potential without compensation controls that adjust its flow temperature automatically. 

See our guide to which boilers are most energy efficient. 

Low-carbon heating systems

In order to reach the UK's net zero target by 2050, we'll all need to eventually install low-carbon heating systems. Many are available to install now, with schemes designed to financially reward people who use renewable energy to heat their homes.

Find out more about low-carbon heating, including how it works, the costs and if it's suitable for your home, in our guides on:

• Solar water heating Solar thermal panels that use heat from the sun to heat water to use in your home.
• Ground source heat pumps A network of water pipes buried underground, extracting natural heat from the ground that is then transferred to your home heating system. 
• Air source heat pumps Works in a similar manner to a ground source heat pump, but instead extracts heat from the air, which is then boosted to a higher temperature using a compressor.
• Electric central heating Reduces carbon emissions from your home (although, only zero carbon if the electricity is produced by renewables)

You can still reduce your carbon footprint with a gas or oil boiler in our top tips to reduce your heating bills.

Choosing the right size boiler for your home

Choosing the right size includes two things: its physical size (whether it will fit in the space you have designated for it) and its heating/hot water capabilities. The latter is measured in kilowatts (kW) and is often just referred to as 'boiler size'.

The correct boiler size will be something unique to you and your home, as it depends on many things, such as how many bathrooms or radiators you have and how many people live in your home.

However, the general rule is the more heat and hot water you use, the higher a kW boiler you'll need. Choosing the right size is something your heating engineer can help with. 

We give 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.  

In the tables below, see which is the right size boiler for you, according to the Heating Hub that provide independent and expert advice on heating systems.¹

It's always good practice to ask the engineer what size boiler they think best fits your requirements. Use the search tool below to find a local expert Which? Trusted Trader.

Buying a reliable boiler

Reliability is by far the most important factor that will influence which one you'll buy, so we go to great lengths to separate the good from the bad brands in terms of reliability.

In 2022, we surveyed 9,722 people who bought a boiler in the past six years and asked what year their boiler first developed a fault (if at all). From this we calculate how many boilers remain fault-free within the first six years.

As you can see in the graph above, there's a big difference between the best and worst. After six years, you're almost twice as likely to have experienced a fault with the worst brand than with the best.

Best boiler for a small flat

If you live in a small flat with one bathroom, then a combi boiler is the ideal choice. They don't need space for a hot water cylinder or a large cold water feed tank, which means the boiler doesn't take up much space.

We'd recommend a small combi boiler that has an output of less than 24kW. Make sure you select one of our Best Buy small combi boilers.

Find out if you're eligible for a free boiler or grant.

Best boiler for a two- or three-bedroom house

For a mid-sized family home, the choice will be between a mid-sized combi boiler or a small heat-only boiler. If you have multiple bathrooms and a large family with room to store a hot water cylinder and cold water storage tank, then the benefits of a heat-only boiler may start to outweigh the benefits of a combi. 

A trained heating engineer will be able to help you with your decision after conducting a survey. But make sure you get a Best Buy mid-size combi boiler or small heat-only boiler.

Best boiler for a four-bedroom house

For a larger home, the best choice is likely to be a heat-only boiler. You'll need space for a hot water storage cylinder and a cold water feed tank in the loft, but for a larger home with multiple bathrooms, a heat-only boiler is nearly always the best option.  

Depending on the size of your home and how well insulated it is, you'll need either a small or mid-sized heat-only boiler.

Best boiler for a home with low water pressure

If you live in an area with low water pressure, or if you live in a large home where you've converted the loft and don't have space for a cold water feed tank, then a system boiler could be your saving grace.  

System boilers don't require a cold water feed tank and also use a pressurised system, which makes low mains water pressure much less of an issue. 

Make sure you pick one of the best brands from our system boiler reviews.

Keep yours in tip-top condition by getting the best boiler service.

How to get the best boiler installation

Leave installation to the professionals. You can find a qualified heating engineer on the Gas Safe Register or use Which? Trusted Traders. 

However, even though you won't be the one physically installing it, there are still big decisions that need to be made. 

Read on to find out what you need to ask and tell your engineer when they visit to give you a quote, what you should expect from a proper installation quote and checks you can carry out after the new one is installed.

Getting a boiler installation quote

When you get a heating engineer to assess your home and give you a quote, it shouldn't be a quick conversation. A good installer should take the time to conduct a full survey of your home, learn about your heating and hot water requirements, and only then give you recommendation on the type and brand for your home. 

Here are six questions to think about:

1. How do you use your hot water? Do you regularly need hot water to be supplied to more than one tap or shower at the same time?
2. Do you have, or plan to have, a pumped power shower? Combi boilers aren't usually compatible with a shower that has a powerful electric pump, so you'll have to ditch the power shower if you go for this type or get a heat-only or system boiler.
3. Do your hot water demands change through the year? Do you regularly have friends staying over, or do you host large parties or Christmas gatherings? If there are going to be big spikes in your hot water demand, get a boiler that can handle this.
4. Are you planning any home improvements? Let your installer know if you're thinking about adding an extension, loft conversion, new bathroom or underfloor heating. Any home improvements you have in the pipeline may change their recommendation
5. Are you having any problems with your current heating system? Are radiators taking too long to warm up? Is the flow rate of your water poor? Tell your installer about any concerns or performance issues you have with your current system.  
6. What boiler brand do you want? Our 2021 boiler survey found the worst brand to be nearly twice as likely to develop a fault in its first six years than the best. Some engineers are incentivised to install boilers from particular brands, so be sure they're making a recommendation that benefits you, rather than them. 

We think a good installer will mention some or all of the following below.

1. How will you dispose of condensate? This pipework takes water from the boiler away to the drain. External pipework should be kept minimal, but if there needs to be some the installer should ensure its protected from freezing temperatures, in accordance with manufacturer's instructions
2. How is the boiler water treated? Heating systems build up sludge over time causing cold spots on radiators and long heat-up times. Systems require cleaning and flushing: a gravity flush for most, but a power flush if the system is heavily sludged. The cost of a power flush for a five-radiator system can range from £300 to £750, with an average cost of £481 (based on quotes from 24 Which? Trusted Traders, February 2022). When refilling your heating system post-clean, ensure the installer adds a chemical inhibitor to slow down the formation of sludge, corrosion and scale build-up.  
3. Do I need system filters/scale reducers? Installing a new boiler into a dirty heating system will lead to future reliability problems. Filters typically cost between £70 and £200 (Screwfix, 2021), and prevent sludge and debris entering your boiler, prolonging its life. Scale reducers are useful for hard-water areas and again help prolong the life of the boiler. Ask your installer if you need them.
4. How big will the plume be? This is the water vapour leaving your boiler flue. Ask the installer how big a plume you're likely to get and where it will be situated. Will it bother neighbours? If needed, the plume can be taken away using an additional pipe.
5. Do I need radiators replacing? Older ones may be inefficient or have internal corrosion, so they might need replacing. Ask the installer for advice.
6. Any additional energy-saving measures? Since 2018, Boiler Plus legislation requires each new gas combi boiler installations to include at least one of four energy-saving measures: flue gas heat recovery, load-compensating thermostats, weather-compensating thermostats or smart heating controls. Get your installer to advise, or read more about boiler controls and thermostats.

New boiler installation costs can typically be anywhere from around £1,400 to £7,000, so we recommend getting at least three quotes to ensure you're getting the best deal. Don't be taken in by any headline discounts, look at the total price for the boiler and labour charges.   

Some installation companies might suggest a replacement boiler rather than letting you choose your preferred model. This is because many heating engineers are incentivised to install particular brands.

So it's vital that you check your heating engineer's recommendation against the views of their peers. We surveyed 153 Which? Trusted Trader heating engineers in June 2021, to find out what they really think of the different boiler brands on the market. Read our boiler brand reviews to find out what they said.

What is Boiler Plus?

The UK government introduced the new Boiler Plus legislation in 2017 to govern new gas boiler installations. Since 2018, the regulation requires that all new gas boiler installations in England:

• Regardless of type, must have a minimum ErP efficiency of 92%
• Must have timer and temperature controls included
• If it's a combi boiler, additional energy-saving measures must be installed:

1. Flue gas heat recovery system This reuses heat from your boiler that would otherwise be wasted, increasing its efficiency.
2. Load-compensating thermostat This adjusts radiator temperature to be hotter when your home is cold and cooler when your home is close to the desired temperature.
3. Weather-compensating thermostat The same as load-compensating, but instead based on the temperature outside the property.
4. Smart heating controls With automation and optimisation functions so you can control your heating remotely through a smartphone

This is all to make gas boilers as efficient as possible, reducing their environmental impact and saving money on your bills. 

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

Thinking of getting smart heating? Read our smart thermostat reviews and smart radiator valve reviews.

What should be included in a boiler installation quote?

Quotes should be clear and correctly itemised so you can clearly see what your money is paying for. However, we've seen many installation quotes that are difficult to understand. 

Here's what you should look for:

1. The brand, model and price of the boiler being installed There should be an explanation on why it's been recommended, with reference to its type (combi, heat-only or system) and size.
2. Extra heating controls These should be costed for and listed separately.
3. Location There should be an explanation of whether the new boiler will remain in the same place as the previous one, or if it needs to be moved. For the latter, it should explain why.
4. Water treatment Cleaning is required, but the method will depend on how dirty of heating system is. The installer should advise you on this.
5. An overview of labour costs This can vary depending on the amount of work that needs doing. Expect it to be higher if the new boiler needs installing in a different location. 
6. System balancing/Post-installation costs It should be mentioned by the engineer that they will make the necessary checks after installation, such as checking that your radiators are balanced and are working.
7. Explanation of the warranty This should detail what needs to be done to maintain the terms of the warranty your boiler comes with, for example getting annual service.

Checks after your boiler installation 

After installation, your engineer should complete a series of safety and performance checks to make sure it's working correctly. 

The results should be recorded in the back of the instruction manual; this forms part of the benchmark process that's important for the warranty. You should also make sure your engineer registers it with the manufacturer to activate the warranty.

If, after these checks, you notice cold spots on radiators or they're taking a long time to heat up, this could be a sign that your system hasn't been balanced or cleaned properly, so you should contact the installer immediately.

Ready to get a new boiler installed? Read our guide on how much a new one costs.

Which? Trusted Trader boiler installers

Getting the best boiler installation depends a lot on the installer you choose for the job, so pick a Which? Trusted Trader, all of whom have passed our stringent standards to become accredited. 

To replace a gas boiler, the installer must be Gas Safe registered, so ask to see a registration card or check the Gas Safe Register. 

Choose a Which? Trusted Trader for an unbiased, expert opinion.