Tired of feeling the pinch when it comes to heating your home? We hear you! With the cost of heating only expected to rise, it's time to consider upgrading your boiler. Buying a boiler that's more efficient has the potential to save you a significant amount of money each year - even if you live in a smaller home.


At Toolstation, you'll find three different boiler types: combination (combi), system and heat-only boilers. All three can be powered with gas, electricity, or liquid petroleum gas (LPG). The right boiler for you will depend on a range of factors, including the size of the building, the space available for a heating system, the number of bathrooms you have, the mains water pressure, and even the type of boiler you already use.


When you’re buying a boiler, make sure you get it properly installed by a qualified tradesperson – such as a Gas Safe Engineer. 

Types of Boiler

You'll find three main types of boiler: combi, system and heat-only. Combi boilers heat water on-demand within the boiler, while system and heat-only boilers store hot water in cylinders in advance.

Combi Boilers

Combi Boilers

Combi boilers are a single unit which provide water for hot taps and showers, as well as central heating. Cold water is taken from the mains and heated within the boiler unit. They’re easy to install and often have high water pressure, as they rely on the water pressure from the mains supply.


Combi boilers don’t rely on water tanks, making them ideal for smaller houses and flats short on space. Because water is heated by the boiler itself, you get hot water on demand – no worrying about the hot water running out when you’re showering! New gas combi boilers can also be up to 98% efficient, meaning only 2% of the energy you’re paying for is wasted.


Combi boilers are ideal for smaller properties like two-bedroom flats or terraced houses. However, they may not be suitable for larger properties with multiple bathrooms or high hot water demands – as they heat water on-demand instead of storing it. And if you’re in an area with low mains water pressure, you may be better off with a system or heat-only boiler, as these will likely provide higher water pressure.


  • Compact and highly efficient

  • Easy to install

  • Hot water on demand

Things to Consider

  • Could struggle to keep up with demand of a larger property

  • Less suited to areas with low mains water pressure

Shop Combi Boilers
Heat-Only Boilers

Heat-Only Boilers

Heat-only boilers, also called regular boilers, are made up of three parts: the boiler, a hot water tank, and a cold water tank. They provide hot water to radiators and the two tanks which send water to taps or showers. They’re compatible with solar panels, and can also be fitted with an immersion heater meaning you can get hot water if your boiler fails.


If you have a larger property with many bathrooms or use a lot of hot water, heat-only boilers are a better option. They have a consistent supply in the tank and don't rely on water pressure from the mains supply. If you have low mains water pressure, a regular boiler is ideal because you’ll have a consistent supply from the tanks. At Toolstation, you'll find our heat-only boilers are electric powered.


The main consideration with heat-only boilers is how much hot water you use – if you use a lot, you could run out and need to wait for it to heat up again. If you don't use much, heating up water that may not be used could be a waste. Installation can also be complex because there’s lots of pipework – and the tanks require much more space and limit installation options.


  • Ideal if you have higher hot water demands

  • Consistent water pressure

  • Compatible with solar panels

Things to Consider

  • Tanks use a lot of space

  • Installation can be more complex

  • You could run out of hot water

Shop Heat-Only Boilers
System Boilers

System Boilers

A system boiler is essentially an updated version of a heat-only boiler, and made up of a boiler and a hot water tank. Rather than storing cold water in a separate cold water cistern, it’s instead supplied to the boiler via the mains. You can get hot water on demand and heat your radiators using the hot tank. System boilers are also compatible with solar thermal – energy created from solar panels.


System boilers are ideal for properties with multiple bathrooms that may be using hot water at the same time, as you won’t struggle with low water pressure. And, because you don’t need to worry about a cold tank, and most components are found within the boiler, installation is more flexible.


If you have an older central heating system, modern system boilers may be too powerful – as the system may struggle with higher pressures. These boilers may not be suitable if you live in a small terrace or flat, because you need room for the hot water tank. And like regular boilers, once the hot water has run out you’ll need to wait for it to heat up again.


  • Water pressure won’t drop if you have multiple bathrooms in use

  • Easier and fairly flexible to install

  • Compatible with solar thermal

Things to Consider

  • Old central heating systems may struggle with high water pressure

  • Require space for hot water tank

  • Hot water can run out

Shop System Boilers

Boiler Fuel Types Explained

Gas Boilers

Most boilers in UK domestic properties are gas powered. These boilers are connected to the gas supply via the national network and offer a convenient and reliable method to heat a home.


Gas is often cheaper than other types of fuel such as electricity, making it a more financially viable option – especially with the UK cost-of-living crisis and energy bills continuing to rise.


Whilst choosing gas as your boiler fuel may have lower monetary cost, it does come with an environmental cost – as these gases release carbon emissions into the atmosphere. Not only this, but gas as a fuel isn’t 100% efficient – at least 2% of the gas will be wasted, but this can go up to 30% for older boiler models.


  • Convenient and reliable

  • Often cheaper than electricity

Things to Consider

  • Carbon emissions released

  • Not 100% efficient, some energy will be wasted

Electric Boilers

Electric boilers are ideal for small properties, and larger energy-efficient buildings, such as new-build three-bed semi-detached homes. These are ideal if the building cannot be connected to gas, or for high-rise flats, and are very easy to install with no flue to consider.


Electric boilers are 100% efficient – meaning no energy is wasted whatsoever – and they don’t rely on combustion so there’s no risk of a hazardous gas leak. Because of this, they don’t need annual servicing by a gas safe engineer – meaning you’ll be saving money on check ups!


When choosing an electric boiler, you need to make sure you pick the perfect size for your space. Choosing a boiler that’s too small will mean it’ll work too hard – and as electricity tends to come at a higher cost than gas, you may end up spending more money and won’t benefit from their efficiency. As electric boilers rely on a strong electrical connection, they may be less suited to homes with old wiring and lower voltage.


  • 100% efficient and carbon neutral if on a renewable tariff

  • Easy to install and no gas flue to consider

  • Zero risk of gas leak and no need for annual servicing

Things to Consider

  • Picking the right size is crucial to ensure 100% efficiency

  • Requires good electrical conection with good supply voltage

LPG Boilers

LPG stands for Liquefied Petroleum Gas, which is transported and stored in gas canisters near the boiler. These boilers are cheaper to purchase compared to oil and gas, around half the cost.


They’re also more compact, making them suitable for smaller homes.


Like oil, LPG needs to be stored in a tank nearby, and replacement fuel has to be ordered regularly – meaning you’ll need to keep a close eye on your usage. And whilst the cost of the boiler is lower, LPG is more expensive per kWh than oil and gas – so it’ll be pricier over time.


  • Compact, making them suitable for smaller homes

  • Cheaper initial cost than gas boilers

Things to Consider

  • Need to order fuel in advance

  • LPG is more expensive per kWh than oil and gas

Key Boiler Features

Smart Heating

Smart heating controls allow you to control your energy usage from your phone, tablet, or computer so you don’t waste money heating empty rooms. This can save you money on your energy bill in the long run.


A boiler can become ‘smart’ by linking it up to a smart thermostat, which allows you to control the heating in each individual room. Smart "learning" thermostats can also learn your daily routine and heating preferences. They turn on your radiators when you're likely to need them, making it easier to manage your energy use. Learn more about smart thermostats in our Smart Thermostat Buying Guide.


Most boilers can be made ‘smart’, including combi, system and heat-only models. However, check with the boiler manufacturer before investing in smart heating.

Boiler Size

When talking about the size of a boiler, it generally means the boiler’s kWh capabilities, rather than its physical size.


When you’re thinking about the size of the boiler you need, most people consider the number of radiators you have as a guide. For example, if you want a combi boiler and have 10 radiators in your home, you’ll need a 24-27 kWh boiler. However, if you’re using a heat-only or system boiler, you’ll want a 12-15 kWh model.


For combi boilers powering 10 to 15 radiators, you’ll want a 28 – 34 kWh model, but for heat-only and system boilers, you’ll want a 18 – 24 kWh boiler. If you have 15 to 20 radiators, you need a 30 – 40 kWh combi boiler, or a 32 – 40 kWh heat-only or system boiler.

Energy Rating

With energy costs rising rapidly, energy classification has become more and more important. Large appliances, including boilers, are given a rating from A to G, depending on how energy efficient they are. This way we can reduce the energy we waste and use more of it to efficiently heat our homes and offices.


All modern condensing gas boilers will be at least 90% efficient, which gives them an A rating – the highest energy rating an appliance can get. However, older non-condensing models (which are no longer sold) could be as low as 60%, which gives them the lowest energy rating of G.


If you’re still using an old non-condensing gas boiler, you’ll notice a big difference in the cost per year if you upgrade to a modern alternative!

Hydrogen Ready

As the UK makes an effort to be carbon neutral by 2050, the gas supply will be 100% hydrogen rather than fossil fuels before 2030. As a fuel, the only emissions hydrogen emits is water – making it very clean and environmentally friendly.


At Toolstation, you’ll find 20% hydrogen-blend ready gas boilers. These are prepared to use a 20% blend of hydrogen and 80% fossil fuels from as early as winter 2023, when the UK government hopes to begin reducing the reliance on fossil fuels.


Manufacturers are committing to keeping hydrogen boilers and hydrogen-blend ready boilers at a similar cost to standard gas boilers, so it’s a good idea to look out for these models if you’re looking to upgrade yours.

Condensing vs. Non-Condensing

A condensing boiler features an element that captures excess energy that would have otherwise been lost, by condensing water vapour within the boiler unit. Non-condensing boilers are older and don’t have this energy-saving feature. All boilers sold nowadays are condensing boilers in line with the law. These are at least 90% energy efficient, compared to old non-condensing models which could be as low as 60% efficient.


Upgrading your boiler from an old non-condensing one to a condensing model is not only better for the environment, but can harness extra energy to heat your home or office while potentially reducing your energy bills.


If you’re still using an old boiler, the investment in a new condensing unit may well be worth it for the energy and carbon savings you could make.

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Frequently Asked Questions

What is a combi boiler and how does it work?

How much does a new boiler cost?

What type of shower can you have with a combi boiler?

How do you install a boiler?

What is the best combi boiler?

What is a biomass boiler?

What is the best type of boiler?

What is a condensing boiler and how does it work?

What is a boiler flue?

Who qualifies for a free boiler grant?

What are the different types of boiler systems?

How much is an annual boiler service?

How long does a boiler last?

What is the optimum temperature to set a combi boiler?

What is a heat-only boiler?

How does a boiler heat water?

What is a system boiler and how does a system boiler work?

How efficient is my boiler?

How do you get a boiler certificate?

What is the most energy efficient boiler?

What size boiler do I need?

What is the alternative to a gas boiler?

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