Different types of boilers explained

What are the different types of boilers?

The three main types of boilers found in UK homes are:

• Combi boilers
• Conventional (heat-only or regular) boilers
• System boilers

Each type comes with its own features and benefits depending on your home’s heating and hot water needs. There are also other, less common types of boilers—like back boilers, which are older systems usually installed behind fireplaces. These are rarely used in modern homes and are generally being phased out in favour of more efficient systems.

Combi boilers

Also known as combination boilers, combi boilers are one of the most popular choices as new boilers in modern homes. They combine a water heater and central heating boiler into one compact unit, which means you don’t need a separate hot water cylinder or cold water tank.

How do combi boilers work?

Combi boilers heat water directly from the mains when you turn on a tap. There’s no need for a storage tank—hot water is delivered on demand, so you get instant hot water without waiting for a cylinder to fill up.

Pros of combi boilers

• Compact and space-saving: Great for smaller homes or flats since there’s no need for a separate water tank.
• Instant hot water: You get instant hot water on demand, so no waiting around or worrying about running out.
• Energy-efficient: Only heats water as you use it, which could help cut down on your energy usage and bills.

Cons of combi boilers

• Not ideal for big households: They can struggle to keep up if multiple taps or showers are used at the same time.
• Relies on good water pressure: If your mains pressure is low, you might not get the best performance.
• No hot water back up i.e. cylinder, should your boiler breakdown

Conventional boilers

Conventional boilers—also known as heat-only or regular boilers – often require both a hot water cylinder and a cold water storage tank, usually placed in the loft. Conventional boilers can also be connected to an unvented cylinder, which allows use of water straight from the mains, so a cold water tank isn’t always needed.

How do conventional boilers work?

Conventional boilers use a cold water tank to store and send water to the cylinder where the boiler heats the water and sends it to the radiators and taps as needed. 

Pros of conventional boilers

• Great for larger homes: They’re perfect if you’ve got lots of people or multiple bathrooms, as they can keep up with high hot water demand.
• Compatible with older systems: A good option if your home already has existing pipework and radiators that are part of an open-vented system.
• No stress with multiple taps: Because they store hot water in a cylinder, you can use more than one tap or shower at the same time.

Cons of conventional boilers

• Takes up more space: You’ll need space for both a hot water cylinder and a cold water tank, often up in the loft.
• Hot water isn’t always ready: Once the cylinder runs out, you’ll have to wait for it to heat back up.
• Installation can be tricky: If your home doesn’t already have this setup, getting it installed can be a bit more involved.

System boilers

System boilers feature elements of both combi and conventional systems. They take water directly from the mains, like combi boilers, but also store hot water in a cylinder, similar to conventional boilers.

How do system boilers work?

A system boiler normally operates alongside either an open vented hot water cylinder or an unvented hot water cylinder to deliver hot water throughout your home.

System boilers take water directly from the mains and heat the water that’s stored in a hot water storage cylinder. This is then used for central heating, as well as showers, sinks, and other hot water needs.

Pros of system boilers

• Perfect for homes with multiple bathrooms: The hot water cylinder stores hot water, so several taps or showers can be used at once without pressure drops.
• No need for a cold water tank: If you choose a system boiler with an unvented cylinder it can free up space in the loft, making it ideal for homes without attic storage.
• Easier to install: Many of the key components are built into the boiler, which can make installation quicker and simpler.

Cons of system boilers

• Needs space for a hot water cylinder: You’ll need a cupboard or dedicated area for the cylinder.
• Hot water isn’t always instant: Once the cylinder is empty, you’ll have to wait for it to reheat.
• Not the most efficient for low usage: If your household doesn’t use much hot water, you might end up heating more than you really need.

What boiler do I need?

Still unsure which type of boiler is best for your home? Let’s recap:

• Combi boilers are best for small to medium-sized homes with one bathroom and moderate water use.
• Conventional boilers suit large homes with high hot water demand and existing traditional systems.
• System boilers are ideal for larger homes where space is a premium which will allow for a sealed heating system to be installed.

When choosing the right boiler for your home, you’ll need to consider the size of your home, as this will directly affect the size of the boiler that you need. You’ll also need to take into account how many people live there and how often you use hot water.

Expert gas boiler servicing you can rely on

No matter which type of boiler you choose, keeping it running smoothly is key to a warm, comfortable home—and that’s where we come in.

At HomeServe, our Gas Safe registered engineers are here to help with everything from regular servicing to emergency repairs. Book your Gas Boiler Service today and let us handle the hard work, so you can enjoy peace of mind all year round.