James Elston

Published April 9, 2024

It is important to know what type of boiler you have, especially if the boiler requires repairs. There are three main types of boilers – combi, conventional/regular and system.

Each of these boilers will also have a different fuel source, such as electricity, gas, oil, biomass or LPG.

Whether you’re looking into a new installation, need a repair, or just want to understand your central heating system better, you’re in the right place! This article will briefly touch on different boiler types before providing you with information on how to identify what type of boiler you have. 

Identifying Your Boiler: A Cheat Sheet

Knowing about the different types of boilers will not only inform you whether you have the right type but can also help answer the question “What size boiler do I need?” if your current type is not meeting your hot water demands.

Below we’ll discuss the different boiler types as well as the different fuel sources that power boilers and heat up water.

Combi boilers

A combi boiler (combination boiler) is a fantastic choice for smaller homes due to its efficiency and compact size. These multitaskers take care of all your hot water and heating needs.

Thanks to their ability to save space, combi systems are a favourite in UK homes, particularly for new installations.

Unlike traditional systems, combi boilers draw water directly from the mains. This means they don’t need a hot water storage cylinder or a cold water tank, saving precious space in your home.


Check for five copper pipes emerging from the bottom of the boiler – this is a telltale sign. You’ll also notice that there is no external pump or hot and cold water cylinders. A combi boiler is usually small, compact, and is always connected to the water mains. 

System boilers

System boilers offer the best of both worlds: the efficiency and compactness of a combi boiler with the capacity to handle higher demands like a regular boiler.

A system boiler doesn’t need a cold water storage tank because most of its heating components are built into the system, making it a great choice for modern homes.

These boilers heat water using a heat exchanger and store it in a hot water cylinder, ready for use. The system distributes hot water to radiators for heating and taps as needed, ensuring a consistent supply.


Generally, you’ll see three copper pipes coming from the bottom of a system boiler unit, which is different from the five you’d find with a combi boiler.

A system boiler also has a hot water cylinder, where hot water is stored for use. This type of boiler does not have an external pump or expansion tank.  

Regular boilers

Regular boilers, also known as heat-only or conventional boilers, are a traditional heating solution in the UK, particularly for large homes.

These boilers, paired with a cold water tank and a hot water cylinder, are large enough to ensure there’s always enough hot water for everyone and the central heating system.

Water is supplied to the boiler from a cold water storage tank (usually in the loft) and is then heated and stored in a separate hot water tank (usually in your airing cupboard).


To spot a conventional boiler, check for two copper pipes at the top and one at the bottom of the boiler. The main giveaway is the presence of both a hot water cylinder and a cold water storage tank. A regular boiler also has an external pump.

Gas boilers

Gas boilers are the most common type of boiler in the UK. These boilers use natural gas piped to the home from the national grid. Gas boilers are highly efficient, especially thanks to modern condensing technology, which recycles the gases back into the boiler for heating instead of releasing them into the environment.

The boilers work by burning gas to heat water, which is then circulated through the home. 


You’ll notice a gas supply line connected to your boiler. There will also be an exhaust flue on the outside of your house, through which the boiler vents byproducts from the combustion process.

Electric boilers

It will come as no surprise that electric boilers use electricity to heat water. This is a much more environmentally friendly heating solution when compared to fossil-fuel-burning boilers. 

Electric boilers are very efficient, as almost all the electricity used is converted to heat. Because there are no requirements for a gas supply or flue, this type of boiler is often more compact. 

If you want to know more about electric boilers vs gas boilers, read our comprehensive guide.


Electric boilers lack a flue exhaust and fuel supply line. There will be an electrical connection that powers the heating elements. You can also identify an electric boiler by how quiet it is – it is much less noisy than its gas and oil counterparts.

Oil boilers

Oil boilers are less modern than electric and gas boilers. These boilers use oil as fuel, making them a great alternative solution for off-grid homes. 

Oil boilers tend to have a high heat output, so they’re great for larger homes or very cold climates.


An oil boiler will have an external oil storage tank connected to the boiler with a fuel line. The boiler will give off a distinct oil smell. 

Biomass boilers

Biomass boilers use organic materials for fuel. This can include wood chips, wood pellets or logs. These boilers are considered to be highly sustainable and environmentally friendly. 


Biomass boilers are generally larger than gas and electric boilers. They’ll have a large chamber for burning the fuel. The flue will emit visible steam or smoke when the boiler is in use. 

LPG boilers

Liquefied petroleum gas (LPG) boilers use LPG as the fuel to heat water. These boilers are often found in homes not connected to the national grid. 

They’re as efficient as gas boilers and produce less emissions than an oil boiler. 


You can identify this type of boiler by an LPG tank, which is either above or below ground, but always outside of the home. There will also be a fuel supply line connected to the LPG boiler and an exhaust flue. 

Boiler Conversion Possibilities

Considering a switch to a more efficient boiler system? Converting your existing regular boiler can be a smart move towards better efficiency and energy savings.

Many older boilers, particularly those with separate water tanks, can be upgraded to newer systems, like combi boilers or system boilers. These modern boilers are more energy efficient and can help save on electricity bills and reduce your home’s carbon footprint.

Upgrades can be as simple as adding advanced controls, like a smart thermostat, for better heat management or as comprehensive as replacing your boiler with a more efficient model.

Make sure you read our guide on the best smart thermostats if you’re considering one.

If you’re thinking about a boiler conversion or upgrade, it’s important to weigh your home’s needs and the benefits of new, efficient systems. Eco Happy is here to guide you if you have any boiler-related or upgrading queries.


How often should I service my boiler?

No matter whether you have a combi, system, or regular boiler, you should service your boiler annually. Regular servicing ensures it operates efficiently, identifies water or gas leaks, and maintains optimal performance.

Can I switch my boiler fuel type?

The only way to switch your boiler fuel type is to install a completely new boiler. For example, if you have an electric combi boiler, you’ll not be able to change the same boiler to work with gas – you’ll have to get a new gas combi boiler. 

What should I do if I can’t identify my boiler type?

Your boiler’s manual should provide you with information on the type of boiler you have. If you’ve lost the manual, you can always consult your boiler brand’s website or contact their customer service for assistance. Lastly, you can call out a heating engineer and have them come asses what type of boiler you have. 


Thanks to this handy guide, you will know what type of boiler you have!

Remember, knowing your boiler type is practical. It helps when you need a repair, want to purchase a new boiler, or just want efficient heating in your home.

If you have questions or need further advice, reach out to Eco Happy – we have all the eco-friendly boiler options you could want!

James Elston

Boiler Expert

James Elston is the top boiler replacement and heating expert at Eco Happy. He has over 20 years of experience in the industry, focusing on Gas Safe boiler installations and offering home-heating and energy-saving solutions to homeowners across the UK. From sourcing the most energy-efficient combi boiler to providing specialist heating advice, James ensures that Eco Happy maintains the highest standards and best customer service.

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