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Boilers Explained: A Full Guide to Boiler Types, Brands, Prices

Boilers are vessels that heat water for a home’s taps, showers, and central heating system. Boilers use fuel such as gas, oil, or electricity to heat water. The most common types of boilers are combination boilers (known as “combi boilers”), system boilers, and conventional boilers.

Boilers Explained
Boilers heat water for the central heating system as well as showers and taps

Boilers comprise many components, which may differ between boiler types, makes, and models. However, the majority of boilers rely on the following five core components to operate.

  • Burner: A boiler’s burner turns fuel into heat inside the combustion chamber.
  • Combustion chamber: A boiler’s combustion chamber houses the burner and contains the flames produced as fuel burns.
  • Heat exchanger: The heat produced by the burner is transferred to the water via the heat exchanger.
  • Expansion tank: An expansion tank helps to maintain proper water pressure.
  • Controls: A boiler’s controls allow you to make adjustments to various aspects of a boiler’s operation, such as setting the indoor temperature.

Boilers use different types of fuel to produce heat, with the most common boiler fuel being gas, followed by oil, electricity, and hydrogen. Gas boilers draw on your domestic gas supply as a source of fuel while oil boilers require a storage tank in which the oil is kept. Electric and hydrogen boilers run on mains electricity and hydrogen, respectively. Boilers that operate on electricity and hydrogen are heralded as the most environmentally-friendly heating devices, although they are currently quite rare.

Combi, system, and conventional are the three primary boiler types. Combi boilers heat water directly and do not use storage tanks, making them perfect for smaller properties. Conventional and system boilers use an external storage tank to keep hot water ready for use. Conventional boilers additionally use external cold water tanks to supply water and maintain pressure in the heating and domestic hot water systems.

The five best boiler brands in the UK are Viessmann, Worcester Bosch, Alpha, Ideal, and Vaillant. Vaillant and Worcester are premium boiler manufacturers that make high-performance boilers loaded with additional features. Viessmann, Alpha, and Ideal are more affordable brands that offer a good balance between quality and price.

Boilers typically cost £500 – £3,000, excluding installation costs. The price of a new boiler depends on the manufacturer, output, boiler type, and additional features. Expect to pay extra for an external hot water cylinder for conventional and system boilers. Switching from one type of boiler to another increases installation costs significantly.

The right boiler for your property depends on how much central and domestic hot water output you need as well as your available storage space and budget.

Picking the right boiler installer is crucial as the poor installation is one of the leading causes of costly repairs. You’re able to reduce the risk of boiler repairs by getting an annual service and using a reputable installer.

Gas boilers are set to be phased out by the UK Government in 2025, under a law that makes it illegal to install gas boilers in new properties after that date. You are still allowed to keep your existing gas boiler, or replace it with a new gas boiler as long as you’re not doing so in a newly built home. Alternatives to gas boilers include air-source heat pumps, solar heaters, and electric boilers.

Below is our thorough guide to all the crucial information you need to know about boilers, including how they work, what they cost, how to fix them, and more.

How does a boiler work?

The way a boiler works depends on the boiler type. However, generally, all boilers burn fuel to generate heat, then transfer this heat to central heating and domestic hot water. Boilers rely on a set of core internal parts to generate and transfer heat to water.

What are the main boiler parts?

The five main boiler parts are as follows.

  • Burner: The burner converts fuel to heat by burning it. Normally, the heat is then transferred to the water via a heat exchanger.
  • Combustion chamber: The combustion chamber is a normally cast-iron container that holds the boiler’s burner. The temperatures produced by the burner are quite high, and the combustion chamber protects the rest of the boiler’s parts from the extreme heat.
  • Heat exchanger: The heat exchanger is a metal part that separates the burner from the water supply and transfers heat from the former to the latter. System and conventional boilers have a single heat exchanger, whilst combi boilers typically have two: one for central heating, and the other for domestic hot water.
  • Expansion vessel: The expansion vessel allows them to control pressure as the water inside heats and expands. The expansion vessel is able to hold any excess water to ensure that the rising pressure doesn’t damage the boiler’s components.
  • Controls: Controls allow you to adjust your boiler’s settings. Some boiler controls are external, like thermostats, while others are integral to the boiler.

What fuel do boilers use?

Boilers use the following four fuel types.

  • Gas: Gas boilers are by far the most common. Gas boilers get their fuel from your gas mains.
  • Liquefied Petroleum Gas (LPG): Many gas boiler models are convertible to run on LPG, which is suitable fuel for households who are not connected to the nation’s gas grid.
  • Oil: Oil boilers are increasingly uncommon but have the advantage of not relying on the gas grid. Oil boilers require on-site fuel storage.
  • Electricity: Some boilers use electricity to heat water via an electric heating element. Electric boilers are not popular in the UK yet because of the high cost of electricity.
  • Hydrogen: Hydrogen is an emerging fuel for boilers. Hydrogen is more efficient and has lower emissions than alternatives like oil and gas. There are no fully-hydrogen-fueled boilers on the market, but some manufacturers like Viessmann and Worcester produce boilers that can run on a 20% hydrogen/gas mix.

Are gas boilers being phased out?

Yes, gas boilers are being phased out, albeit slowly. Recent UK legislation prohibits the installation of gas boilers in new properties starting in 2025. However, you do not need to get rid of your gas boiler if you already have one installed, and may replace your gas boiler if you do not live in a property constructed after 2025.

Can boilers work with solar power?

Yes, some boilers can work with solar power. Conventional and system boilers can work with two-coil hot water cylinders, the secondary coil of which can be connected to a solar power supply.

What kind of fuel does your boiler use?

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What are the different types of boilers?

The four different types of boilers are listed below.

  • Combi boilers: Combi boilers heat both central heating and domestic hot water on demand. Combi boilers do not have storage tanks to keep water ready for use, so their smaller footprint means combis are good for small homes and apartments. However, combis are not always able to keep up with high demand for hot water since they don’t have any water storage facilities and depend entirely on mains pressure.
  • Storage combi boilers: Storage combi boilers have the same functionality as a combi boiler and heat water directly. However, storage combi boilers have an internal storage tank that allows them to meet a higher hot water demand than a typical combi boiler could handle.
  • System boilers: System boilers heat central heating water directly and heat domestic hot water by passing that central heating water through a coil in an external storage cylinder.
  • Conventional boilers: Conventional boilers work like system boilers with an external storage tank for domestic hot water. The difference between system boilers and conventional boilers is that conventional boilers use external cold water tanks to store domestic hot water and central heating.

What are the best boiler brands?

The five best boiler brands are as follows.

  • Worcester Bosch: Worcester Bosch are a premium boiler brand known for advanced features, such as intelligent filling, weather compensation, and WiFi-enabled controls.
  • Viessmann: Viessmann are a German boiler manufacturer known for well-engineered components like burners and heat exchangers that use smart sensors to increase the boilers’ fuel efficiency.
  • Alpha: Alpha are a lower-cost boiler manufacturer that is nevertheless known for the quality of its products.
  • Ideal: Ideal offer boilers that have all the features a typical family are likely to need. Ideal is a British boiler manufacturer with good warranty periods of up to 12 years.
  • Vaillant: Vaillant are mid-market boiler manufacturer that maintains a good balance between quality and price.

How are boilers installed?

How boilers are installed depends on site-specific circumstances and the boiler type. However, below are the six core steps

  • Remove the old boiler: Installers first remove your old boiler and dispose of it properly.
  • Clean the system: The second step is to thoroughly clean out your existing system and heating pipework.
  • Repair pipework: Installers make any necessary repairs or changes to the pipework to accommodate your new boiler.
  • Fit the boiler: The fourth step in the boiler installation process is to fit the new boiler in its appropriate location.
  • Commission the system: The next step after installing the boiler is for installers to commission the new system, which entails verifying that all system components are working properly.
  • Register the boiler: The final step is to register your new boiler with your boiler manufacturer to activate your warranty. Some manufacturers require that you register the new boiler within 24 hours of installation.

When should boilers be replaced?

Boilers should be replaced every 15 years on average. A typical boiler lasts 15-25 years before it stops functioning properly. However, boilers often lose performance and efficiency much earlier in their lifespan, driving up repair and energy costs. Replacing an inefficient old boiler even if it’s still operational gives you a chance to save hundreds of pounds per year in heating costs, according to the Energy Savings Trust.

How to choose a replacement boiler?

Choose a replacement boiler according to the following six criteria.

  • Central heating output: Central heating output is the heating capacity your boiler provides for the home’s radiators. You need a higher central heating output if you live in a larger property with more radiators, and vice versa.
  • Domestic hot water output: Domestic hot water output is the amount of heat your boiler is able to produce and transfer to the water that flows from your taps and showers. You may need a higher domestic hot water output if you live in a property with more people who may use several hot water taps or showers at the same time.
  • Storage space: Consider how much storage space you have available before you purchase a new boiler. Conventional and system boilers need more space than combi boilers because they have additional external tanks that you need to accommodate on your property.
  • Budget: Budget is another major factor in the decision to purchase a new boiler. Boilers with more output and features are more likely to be expensive. Luckily, most boiler brands have ranges of models to satisfy any budget, and financing is always an option (if you qualify).
  • Energy-efficiency: You may want to purchase a more energy-efficient boiler if you prioritize saving money on your monthly energy bill.
  • Extra features: Think about how much you value-added features like wifi connectivity and weather compensation when you purchase a new boiler.

How to choose a boiler installer?

Choose a boiler installer according to the following three considerations.

  • Budget: Consider your budget when looking at different boiler installers. Some boiler installers will charge higher or lower prices to install the same boiler.
  • Reputation: Make sure you go with a reputable boiler installer with good customer service and experience. A poor installation may save you money in the short run but will be more expensive in the long run if you have to pay more for repairs.
  • Type of installer: Boiler installers come in different shapes and sizes. Larger national boiler installers like British Gas are generally more expensive but come with a longer track record. Online installers can offer lower costs because they aren’t paying rent. Local mum-and-pop installers come between the two in terms of price and offer a local touch.

What are online boiler installation companies?

Online boiler installation companies are boiler installers who operate exclusively online and do not maintain a physical storefront. Online installers are generally newer companies that offer easy online tools to help you find the right boiler for your property. For example, Heatable are online boiler installers that offer significant savings for their customers because they have such a tiny overhead. You can see what boiler models Heatable recommend (along with fixed-price quotes) by filling out their anonymous questionnaire right here on your computer screen.

How much do boilers cost?

Boilers cost £500 – £3,000 (excluding installation) and these prices depend on the following four factors.

  • Manufacturer: The price of your boiler will depend on the boiler manufacturer. Premium brands tend to cash in on their reputation and charge you higher prices.
  • Heating output: Boilers with higher outputs are typically more expensive because they need larger, more powerful to facilitate the higher heating capacity.
  • Boiler type: The type of boiler you purchase has a big effect on your boiler price. Conventional and system boilers are generally more expensive than combi boilers, partly because using these boilers requires you to purchase hot and cold water storage tanks.
  • Additional features: Boilers with additional features, like WiFi connectivity, generally cost more than boilers with fewer extra features.

Installation typically adds between £1,000 and £2,000 on top of the boiler cost. How much you pay to fit a boiler depends on four factors. Firstly, installing a boiler of the same type as you already have costs less than changing boiler types. Switching one boiler type for another one adds to installation costs because such a swap generally entails changes to the pipework and any associated heating infrastructure. Secondly, installing the replacement in a new place costs more, as the engineers have to reroute the pipework from the existing location, which adds to the installation costs. Thirdly, your geographic location dictates how much you pay to fit a boiler. The capital region is the most expensive, whilst other cities typically have cheaper labour, and thus, cheaper boiler installations. Finally, the installer you choose has a direct impact on the costs of fitting a boiler. National companies charge higher fees to fit boilers than local trades and online installers.

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What is boiler financing?

Boiler financing is a payment plan that allows you to pay for your boiler in monthly installments rather than in a single up-front payment. Most boiler distributors offer financing to their customers, with varying options for APR, downpayment, and term length. The distributors are not lenders themselves, and the financing comes from a financial institution. Credit checks are required when you apply for boiler financing, and customers generally need a good credit history to qualify.

How to troubleshoot boiler problems?

You’re able to troubleshoot boiler problems by taking the following three steps.

  • Check the control panel: The first step is to check the control panel to see if any warning signs are flashing on the screen that may give you an indication of what problem your boiler is experiencing. Some boilers have a troubleshooting function in the boiler control panel.
  • Check the thermostat: The second troubleshooting step is to check to see if your thermostat is working properly and is turned on.
  • Check the fuse box: Another possible problem if your boiler isn’t working is that your home electrics have a blown fuse or tripped circuit breaker. Such problems could deny your boiler power.

How to prevent boiler problems?

You’re able to prevent boiler problems by taking the following two steps.

  • Purchase a boiler with a long warranty: Getting a boiler with a warranty of 7-10 years helps you avert boiler problems in two ways. Firstly, boilers with long warranties generally last longer without developing repairs, which is why their manufacturers feel comfortable with offering long warranty terms. Secondly, a long term means that you’re protected against steep repair costs if your boiler malfunctions while under warranty.
  • Get annual boiler service. An annual boiler service identifies boiler problems before they deteriorate and limit the amount you need to spend on repairs.
  • Get a reputable installer. A poor boiler installation is one of the primary causes of boiler problems. Working with a reputable installer is a great way to limit your risk of boiler breakdowns.

What is boiler service?

Boiler service is an annual inspection conducted by a GasSafe engineer to identify problems early and improve the performance of your boiler. An annual service is often a requirement of a manufacturer’s warranty. Boiler service and a gas safety inspection are mandatory if you’re a landlord with boilers in your rental properties. The cost of annual boiler service ranges between £80 and £100.

What is boiler cover?

Boiler cover is a type of coverage package that pays for and facilitates repairs when your boiler breaks down. Boiler cover providers often bundle their plans with other kinds of coverage, like plumbing, home electrics, home security, and pest control.

FAQs about boilers

The following are answers to some common questions about boilers.

What is a boiler used for?

A boiler is used to fulfill two functions. Firstly, a boiler is used to heat domestic hot water. Domestic hot water is the potable water you get when you run a tap or shower. Secondly, a boiler is used to supply heat to your central heating system. The central heating system includes your radiators, pipes, and towel rails, all of which circulate water that your boiler heats.

How does central heating work?

Central heating works by moving heated water through a network of domestic radiators. A boiler heats central heating water by burning fuel to produce heat and then pumps that water through your central heating system. The heat from this water makes the exterior of your radiators hot, thus, in turn, heating the air in your home. Conventional boilers have pumps that move central heating water through your home while combi boilers rely on the circulation of mains water to move central heating water through your radiators.

Is a boiler the same as a water heater?

No, a boiler is not the same as a water heater. Boilers heat water for both domestic hot water and central heating, while water heaters only heat water for use in sinks, showers, and baths. Water heaters are similar to combi boilers in that they heat water directly rather than storing it, but combi boilers have two heat exchangers to accommodate central heating as well as domestic hot water. Water heaters are most common in Northern America, where air-based heating is a more common way to warm a home.

Does a boiler give you hot water?

Yes, a boiler gives you hot water. Boilers use fuel to heat water for both domestic hot water and central heating.

Do radiators use a boiler?

Yes, radiators use a boiler. Radiators are connected to the boiler via your central heating system’s pipework. The boiler heats water and then circulates it through your home’s radiators.

Is a boiler for hot water or radiators?

A boiler is for both hot water and radiators. Most domestic boilers are able to serve both the domestic hot water and the central heating systems. Conventional boilers, for example, heat central heating water directly and then heat domestic hot water indirectly by passing a coil of central heating water through the domestic hot water storage tank. Meanwhile, combination boilers have two separate heat exchangers, which are used to heat the domestic hot water and radiator water separately.

Does a boiler use gas when the heating is off?

Yes, a boiler uses gas when the heating is off for two purposes. Firstly, most boilers keep a pilot light burning to ignite the main burner when you need to use it. This pilot light only consumes a negligible amount of gas. Secondly, your boiler uses gas when the heating is off if it needs to heat your domestic hot water.

What are the 3 types of boilers?

The three types of boilers are as follows.

  • Combi boiler: A combi boiler is a boiler that heats water directly for domestic hot water and central heating. Combi boilers do not store any hot water ready for use.
  • System boiler: A system boiler heats water for central heating directly and indirectly heats domestic hot water by passing a coil full of hot central heating water through a separate domestic hot water storage tank.
  • Conventional boiler: A conventional boiler works in a similar way to a system boiler except it uses a separate cold water tank to maintain water pressure.

What is a combi boiler?

A combi boiler is a type of boiler that heats water directly as you need it and does not require a cylinder to store domestic hot water. Combi boilers are generally the most affordable, space-efficient, and energy-efficient boilers on the market. However, combi boilers struggle to keep up with the hot water demands of larger households.

Which boiler is the best?

Which boiler is the best depends on the following three considerations.

  • Your property size: A combi boiler is well-suited to smaller properties because it does not use separate storage tanks that take up space.
  • Your hot water demands: Larger households are likely to use more hot water so it makes sense to get a boiler with a higher domestic hot water output. Combi boilers may struggle to keep up with larger households so it may be a good idea to consider a system or conventional boiler.
  • Your number of radiators: Homes with more rooms and radiators need a boiler with a higher central heating output.

What is the most popular boiler in the UK?

The most popular boiler in the UK is the combi boiler. Combi boilers are widely used because their small size makes them perfect for smaller homes and apartments. Combi boilers are more affordable and more energy-efficient than conventional or system boilers.

How long should a boiler last?

A boiler should last 15-25 years. You can extend the life of your boiler by using a reputable installer and getting annual service to identify faults as early as possible.

What is best to replace a gas boiler?

An electric boiler is best to replace a gas boiler. Electric boilers run on mains electricity and use an electric heating element to heat water instead of a burner. Electric boilers work a lot like electric stoves.

Which boilers are the most efficient?

Combi boilers are the most efficient boilers because they do not waste energy to keep a tank of water hot throughout the day. Combi boilers only use the energy needed to heat the exact amount of water you need.

Is it wise to buy a new gas boiler now?

Yes, it is wise to get a new gas boiler now. Gas boilers will be phased out starting in 2025 in the UK, but it is perfectly legal to install a new gas boiler in 2024. Gas boilers are the most common type of boiler on the market so it will be easy to find the perfect gas boiler for your property.

Should I replace my 20-year-old gas boiler?

Yes, you should replace your 20-year-old gas boiler. Most boilers last 15-25 years, so a gas boiler that has been in your property for 20 years or more is likely to rack up higher repair costs and be less energy-efficient than newer models.

Should I change my boiler to a combi?

Whether you should change your boiler to a combi depends on the following five factors.

  • Your hot water demands: Combi boilers may struggle to keep up with the hot water demands of larger households.
  • Your number of radiators: Combi boilers can meet the central heating demands of most properties but a conventional or system boiler may be a better choice for larger homes.
  • Your property size: A combi boiler is well-suited to smaller properties because it does not use separate storage tanks that take up space.
  • Energy efficiency: How much your value energy efficiency will be a big factor in your decision to get a combi boiler. Combi boilers are generally more energy efficient than conventional or system boilers because they do not keep a tank of hot water warm throughout the day.
  • Your budget: Combi boilers are generally less expensive than conventional or system boilers. However, switching from one boiler type to another also comes with additional costs depending on the nature of your system. Contact a boiler installer like Heatable to get an idea of whether switching to a combi boiler is likely to be more expensive than replacing your boiler with a conventional or system boiler.