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What Are The Different Types Of Boiler? An Ultimate Boiler Guide

Boilers are a vital part of your heating system, especially over the winter months. They heat up and send hot water to your radiators to warm up your home. All year round, they may be responsible for providing you with hot water itself. But what types of boiler systems are there? And what boiler do you have? It can be difficult to know which boiler is best for your home or water heating requirements, and whether you should stay with your current boiler or make a switch.

This guide is going to look at the different types of boiler and how they might benefit you in your home.

What Type Of Boiler System Do I Have?

It can be difficult to know the different types of boiler, let alone the boiler systems you have in your home. There are three main boiler types used in the UK:

  • A combi, or combination boiler
  • A heat only boiler
  • A system boiler

You can usually tell what type of boiler it is by looking at it. A combi boiler usually has around five pipes coming out of the bottom. A heat only boiler has two pipes coming out of the top of the boiler, and one coming down. A system boiler usually only has three pipes coming down, and there will be a hot water cylinder as part of the boiler. Once you’ve been able to identify your boiler, you can identify whether it is suitable for your current water requirements. 

Read on to find out more about these different boiler types.

The Different Types Of Boiler And Boiler Systems

There are many different types of boilers, but three main ones in the UK: the combi boiler, the heat only boiler and the system boiler. Each boiler fulfills a specific hot water requirement that should meet what your property and family need. This section will break down these three boiler types and explain their benefits to a home.

Combi Boilers

What Is A Combi Boiler?

A combi, or combination boiler, connects directly to the cold water supply and converts it to hot water on demand. If you turn on the hot water tap, run a hot shower or bath, then the boiler will convert that water to hot water and divert it to the desired location. Combi boilers are compact and don’t have a water tank like some other boilers, so take up less space. This makes them useful for smaller properties.

How Does A Combi Boiler Work?

A combi boiler will have a pipe that directly feeds into your mains cold water supply. If you run the cold tap, the mains cold water supply will directly supply water to your tap, bath or shower. If you run the hot tap, then water will be diverted from the cold water supply via your boiler. That means any hot water will have to go through your boiler first, providing hot water on demand. You won’t need to wait for your boiler to heat up to receive hot water directly from a tap.

Your combi boiler also directly heats up water from the cold water supply ready to heat up your radiators and central heating. Cold water is then returned to the boiler to be heated again. The heating is undertaken via combustion through oil or gas, which is why the water is heated immediately. Combi boilers are the most popular type of boiler replacement in the UK due to their ability to instantly heat water.

What Are The Pros And Cons Of A Combi Boiler?


  • A combi boiler heats water instantly, so you don’t have to wait for water to warm up
  • They are small and compact, making it easier to fit them in a cupboard or smaller space
  • Ideal for flats or smaller properties due to their size 
  • Many heating engineers are trained in combi boilers, making it easy to service


  • Combi boilers make it hard for two water outlets (e.g. two showers) to run at the same time
  • If your cold water mains supply is lower pressure than your combi boiler won’t work well
  • Less useful for larger properties as only certain units can be used in tandem

Key Takeaway

If you have a smaller property then a combi boiler is likely the right choice for you. You will have instant hot water on demand and find it easier to slot this boiler into your home. If you have a larger home or lower water pressure a combi boiler might not be right for your property.

Heat Only Boilers

What Is A Heat Only Boiler?

Heat only boilers are also known as a regular boiler. Unlike combi boilers, they connect to a water tank to provide hot water. They will usually have a hot water tank, a cold water tank, and the boiler itself. They feed heat directly to the radiators and have a separate hot water storage tank for instant use. The cold water tank is usually located in the loft or a higher floor, which then feeds down to the boiler.

You might have an old style boiler located in a chimney breast. This has an electric, natural or gas fire in front, and the heat from that is used to heat the boiler. You cannot directly replace this type of boiler and will need to look at heat only or alternative solutions when the time comes to replace your back boiler.

How Do Heat Only Boilers Work?

Heat only boilers work through a series of pumps, tanks and valves. The cold water tank will feed in water from the mains into a hot water tank, which is heated by the boiler. There is usually an expansion tank that will ensure the cold water tank has a constant supply of water available. The hot water tank will be used to supply water on-demand. Pumps will also help to send water to the radiators when central heating is required. These systems also have vents that need to be accessible from the outside, to let out waste air and draw in oxygen.

What Are The Pros And Cons Of Heat Only Boilers


  • Much better for large properties as water can be sent to multiple showers or units
  • More suitable for lower pressure water supplies or older heating systems 


  • They take up more space due to the water tanks, making installation more invasive too
  • They don’t give hot water on demand so you have to wait for them to warm up
  • You can run out of hot water if multiple people are using hot water in one go
  • They are less efficient than combi boilers as water can evaporate or be lost from tanks

Key Takeaways

The main benefit of a heat only boiler is that they are more suitable for large properties and areas with lower water pressure.

System Boilers

What Is A System Boiler?

System boilers are like heat only boilers, but they don’t require a cold water tank. They are closed vent systems that take water directly from the cold water mains to the boiler. All the pumps and expansion tanks are also internal, which makes them an upgrade from the space required by heat only boilers. If you are trying to decide on a heat only or system boiler, then it depends on the water pressure in your area.

How Do System Boilers Work?

System boilers work like combi boilers in that they heat up water directly from the cold water supply. However, they store hot water in a separate tank for on-demand use, which means multiple bathrooms or units that require water can be serviced in one go. System boilers rely on good water pressure from the mains to function.

What Are The Pros And Cons Of System Boilers?


  • They do not require a cold water tank, making them easier to install than heat only boilers
  • They take up less space than heat only boilers
  • System boilers can service multiple bathrooms or units at the same time
  • You can be more flexible with installation than with a heat only boiler


  • They still require an external hot water tank 
  • If the water pressure is low the boiler won’t work effectively
  • Their size may not make them suitable for smaller properties

Key Takeaways

System only boilers are great for larger properties with high water pressure. If you have lower pressure you might need to consider a heat only boiler. Their size makes them unsuitable for smaller properties.

What Type Of Boiler Do I Need?

The type of boiler you need depends largely on the size of your home, the number of bathrooms you have, the age of your central heating system and the water pressure in your local area. As a general rule you may find:

  • You need a combi boiler if you have a smaller property with decent water pressure and a modern heating system. They are easier to install, take up less space and supply hot water on demand.
  • You need a heat only boiler if you have a larger property with multiple bathrooms, older heating systems, and a poor water supply. A heat only boiler doesn’t rely on water pressure from the cold mains, so might be your best option if your local area has poor water pressure. If you have good water pressure and a larger property, you might consider a system boiler.
  • You need a system boiler if you have multiple bathrooms and decent water pressure. A system boiler is preferable to a heat only boiler as it requires less space to install. Unless you have issues with your water pressure, a system boiler might be the best option for a house with multiple bathrooms.

New Boiler Installation With Lloyd’s Gas

Lloyd’s Gas are expert boiler installers, ensuring that your boiler operates at up to 98% efficiency. We’re experienced in all boiler and property types, with decades of experience in boiler installation. Whether you’re in a smaller property that can benefit from a Vaillant combi boiler, or a larger property with heat only or system boiler needs, we can help. We can also offer free advice or consultation if you’re not sure if your older central heating system and water pressure is suitable for a combi or system boiler.

Do you need expert advice on whether you should replace or change your boiler? Contact us at Lloyd’s Gas for your free consultation.

We provide boiler installation services in Manchester & the surrounding areas, for more information on where our services are available, check out our service coverage page.

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