Your guide to the different types of boilers.

It’s important to pick the right type of boiler system for your central heating system and hot water needs, and we’re here to help.

Types of boiler

What are the different types of boilers?

There are three main types of boilers that you can get in your home:

Each boiler type has advantages and disadvantages and the one that’s best for you will mostly depend on your current heating and hot water demands.

If it’s time to get a new boiler then it’s a good idea to consider whether you should stick with the type of boiler system you have or swap to a different type of central heating boiler.

What is a combination boiler (combi boiler)?

A combi boiler is a single stand-alone unit that generates all of the heating and hot water for your home. Unlike other boilers it doesn’t have a hot water tank or separate water cylinder.

Combi boiler

How does a combi boiler work?

A combi boiler uses an integral heat exchanger to heat water directly from the cold mains. This means it’s able to provide instantaneous hot water for your home.

Because combi boilers don’t require a separate water tank, they take up less space than the other two boiler types.

What are the advantages of a combi boiler?

  • Instant heating and hot water. You get it when you need it.

  • Space saving as no separate hot water tank. Ideal for smaller properties.

  • Easy installation. You only need to have one unit fitted.

  • High energy efficiency. Combi boilers are over 90% efficient.

  • Easier to maintain.

What are the disadvantages of a combi boiler?

  • Reduced water flow rates when you’re using hot water at two or more outlets. For example, two showers at the same time.

  • Don’t work well in homes with poor water flow rates and/or poor water pressure.

  • Not compatible with solar water heating systems.

Learn more about combi boilers and whether they’re right for your home.

What is a regular/conventional/heat only boiler?

A regular boiler (or heat only boiler or conventional boiler) only provides heating to your home. They connect to a separate hot water cylinder and a cold water storage tank.

Regular boiler

How does a regular boiler work?

Similar to a combi boiler, a regular or conventional boiler has a heat exchanger that warms water and then uses a pump to transport the water to a water storage tank. The hot water then flows through to the radiators to heat them or into your tap when you switch them on.

The cold water is supplied to your home using the cold water tank, which is typically in the loft/attic. It fills the boiler with the help of gravity.

What are the advantages of a regular boiler?

  • Work well with older heating systems as they don’t rely on mains pressure.

  • Suitable for homes with greater hot water demands as they provide a higher flow rate.

  • Lower replacement costs as regular/conventional boilers are generally the cheapest type of boilers to buy.

  • Can work with solar water heating systems to help lower your bills.

What are the disadvantages of a regular boiler?

  • Hot water isn’t always available on demand so you may need to wait to have a shower.

  • Regular boilers aren’t as efficient as combi boilers as heat is lost when the water is stored in the cylinder.

  • You’ll need plenty of space in your home to house the hot water cylinder and cold water tank.

  • May not be compatible with some newer central heating systems.

Learn more about heat only boilers and whether they’re right for your home.

What is a system boiler?

A system boiler combines a boiler and separate hot water cylinder to provide heating and hot water to your home. System boilers don’t have a cold water tank and many of the components like the pumps and valves that you’ll find separate with a regular (conventional boiler) are in-built with a system boiler.

System boilers are also referred to as closed-vent or system sealed boilers.

System boiler

How do system boilers work?

System boilers work with a hot water cylinder. They’re not “open vented”, which means there are no tanks in the loft and are essentially an updated version of regular boilers.

What are the advantages of a system boiler?

  • Good for properties that need a lot of hot water at the same time, for example multiple bathrooms.

  • No need for a cold water tank.

  • You don’t need any components in the attic, perfect if you’re looking to convert it.

  • Work well with underfloor heating.

What are the disadvantages of a system boiler?

  • The water flow rate depends on the main pressure. So if there’s low pressure in your area the water flow rate throughout your home will be worse.

  • You’ll need to have space for the hot water cylinder, for example an air cupboard.

  • If you use up all the hot water in the cylinder then it’ll take a while to reheat.

Learn more about system boilers and whether they’re right for your home.

Combi boiler

Combi boilers.

These are great if you live in a smaller home. They don’t need a separate hot water cylinder or cold water storage tank, so they could easily fit into a cupboard and don’t take up any of your valuable space under the stairs or in the loft (for example).

More on combi boilers.

Regular boiler

Regular boilers.

If you often use hot water around your home, then a regular - or “condensing” - boiler is probably best for you. They can take up more room than a combi as they often come with a cold water tank as a kind of back up but you’ll have a plentiful supply of water ready to be heated regardless of water pressure or any other issues.

More on regular boilers.

System boiler

System boilers.

Does your home have more than one bathroom? Then a system boiler is a good choice. They’re like a condensing boiler but with a large tank for storing extra hot water. Again, they take up more room than a combi boiler, but you have a constant supply throughout your home when you need it.

More on system boilers.

What is a condensing boiler?

Condensing boilers are designed to heat up your home and water as efficiently as possible and it’s a requirement that every new boiler must be condensing and have an A efficiency rating.

The difference between condensing boilers and non-condensing boilers is the amount of heat that they produce and that condensing boilers achieve over 90% energy efficiency.

What’s the difference between a combi boiler vs a condensing boiler?

Combi boilers are actually a type of condensing boiler so there’s no difference between them as combi boilers use condensing technology.

How do I know what type of boiler I have, a condensing boiler or non-condensing boiler?

If you’ve moved into a new property and you’re not sure if you have a condensing boiler, there are a few ways you can check:

  • Check the install date of your boiler. If you got a new boiler after April 2005 then the regulations will mean it’s condensing.

  • If your boiler has a metal flue then it’ll probably be non-condensing. Condensing flues are usually through an external wall or your roof.

  • If you see steam through an external wall or your roof and a white plastic pipe leading to a drain, then it’s most like a condensing boiler.

If you have a non-condensing boiler in your home then it may be time to get a new boiler, like an energy efficient Worcester Bosch boiler.

Get warm and cosy and save up to £475 on your annual gas bill.1

Plus if you’re an E.ON Next customer save £150 when you buy a boiler through E.ON. T&Cs apply.

Get a new boiler

1 An average household could save up to £475 on their annual gas bill. Savings information for boilers in the UK provided by the Energy Saving Trust, based on a detached house with a boiler rating of G.

Why choose a Worcester Bosch boiler?

They’re fast and economical to run.

Worcester Bosch boilers are A-rated for efficiency, guaranteed to be 94% efficient, helping you to reduce your energy bills.

Smart connected thermostats.

Control your central heating and hot water with the wireless Bosch EasyControl, plus get easy-to-understand graphs on gas consumption and how efficient your heating programmes are.

Awarded Best Buy by Which?

Our new Worcester Bosch boilers build on the award-winning Greenstar range, offering smarter and more powerful condensing boilers with advanced technology to maintain water pressure.

Find out more about our Worcester Bosch Greenstar boilers.