Heatable uses cookies to give users the best possible experience.

View Policy

Black Friday Boilers
We've knocked £100 off, everything.

COVID-19 Notice
We're still installing boilers, safely. Read more.

Types of Boiler Systems Explained (and what you'll need for your home)

Whether you're considering a combi boiler or a conventional boiler, it's super important for you to understand the differences. Here, you'll learn the pro's and con's of each, what they're good at, and what they're useless at.

There are three main types of boilers you can install into your home: combi boilersheat only (regular boilers) and system boilers

The one most suitable for you and your home largely depends on your current hot water demands, but it is also important to consider other factors, such as the age of your current heating systems and the pressure of your mains water supply. 

Should you stay with your current type of boiler? Or should you swap to a different type of central heating boiler? Let’s find out….

Need to know the cost of a new boiler, quick? Find out what replacement you need along with costs (takes 60 seconds).

Different boiler types

Combination (Combi Boilers): What are they? 

combi boiler provides both your heating and your hot water from a single unit, typically wall hung.


Want an exact price on a new boiler? Use our boiler quote calculator (no personal details needed).

They're the holy grail of heating and the UK's most popular type of boiler replacement.

So, how do combi boilers work? 

Combi boilers utilise a metallic heat exchanger to instantly heat hot water on demand, they achieve this via combustion e.g. by burning fuels such as gas or oil.

Heat Exchanger Combi Boiler

This is the biggest distinction of combi boilers, as unlike traditional boilers they do not require a separate hot water storage tank.

Instead, the hot water is heated immediately from a single unit. 

Learn all about combi boilers in our what is a combi boiler guide. 

Curious to know which boiler brand performed worst? Find out in our report of the worst boilers

Pros of combi boilers

Combi Boiler Pros

If you are looking for a boiler that's highly energy efficient, a combi (combination) boiler might be the solution. They can be used to heat the home as well as its water, saving you a wedge on heating bills. 

Their compact size makes them ideal for even the smallest of properties, and since they use the mains to heat water, you will not have to make space for a cumbersome water tank or cylinder. 

Another plus is that because they can instantly heat the water you need; you will not have to wait around for that hot, sultry shower.

Cons of combi boilers 

Combi Boiler Cons

There are a few drawbacks to consider.

Water flow rates are reduced when two or more outlets are being used at the same time.

So, if you have got a larger property with a few bathrooms (which may be used at the same time), a combi might not be the right choice for you. 

Ultimately, a combi boiler can only heat the water which gets fed to it from the mains. So, if your mains water pressure is low, your combi boiler won't work very well.

Combi boiler key points: 

  • The compact design makes them ideal for properties with limited space.  
  • Do not need a hot water storage cylinder.
  • Do not need a cold-water tank.

  • Typically, not suitable for larger properties with multiple bathrooms/or a high hot water demand.  
  • May not be suitable for areas that suffer from low mains water pressure. 

Looking to pay for your new boiler monthly? Refer to our boilers on finance guide for more info.

Heat Only (Regular Boilers): What are they? 

A heat-only or regular boiler has three main components – the boiler itself, a separate hot water storage cylinder and cold water storage tank.

The boiler supplies hot water to both the central heating and storage cylinder, so can provide both hot water and heating water. 

Heat Only Boiler Setup

How do heat only boilers work? 

Regular boilers work by feeding hot water directly to the central heating system i.e. the radiators and storing hot water within a hot water storage cylinder for on-demand use.

Coldwater is supplied to the boiler via a cold-watertank (typically located in the attic/loft), which fills the boiler with the help of gravity.  

Want an exact price on a new boiler? Use our boiler quote calculator (no personal details needed).

Pros of heat only boilers 

Regular Boiler Pros

Heat only boilers can provide a greater flow rate and as a result, are more suitable for larger properties with greater hot water demands e.g. those with multiple bathrooms. 

As they do not require water to be supplied at high pressure via the mains, they are a good option for older heating systems that may not tolerate the high pressure of a closed system. 

Alternatively, they are also a good choice for areas that have low water pressure mains supplies, that typically struggle to supply adequate water pressure required in combi and system boilers. 

Check our new boiler costs guide and use our boiler size calculator if you want to get a better understanding of how our fixed price boiler quote tool works. 

Cons of heat only boilers 

Regular boiler cons

A conventional boiler may not be compatible with some newer heating systems, and you might have to wait a while for the water to reach the right temperature. 

Also, bear in mind that you will need somewhere roomy to store the boiler's cylinder and water tank. Since the cold-water cistern needs to be installed directly above the boiler, this may also limit where you can install the boiler too. 

Having issues with your combi boiler? Read our boiler problems and solutions for quick troubleshooting guidance. 

Heat only boiler key points: 

  • Good choice for properties with multiple bathrooms and high hot water demands.  
  • Ideal for areas that suffer from low water pressure. 
  • Good choice for those with older/traditional heating systems that cannot tolerate high pressure. 

  • Since they require a cistern tank, they demand more space and limit boiler installation options. 
  • A cistern in the attic is prone to freezing during winter and if it leaks can be problematic. 

Is your boiler leaking or losing pressure? Use our quick and easy tool to get your fixed price boiler replacement

System Boilers: What are they? 

System boilers are essentially an upgraded version of the regular or heat-only boiler. They can provide both hot water on demand and heating water for your radiators. 

How do system boilers work? 

System Boiler

Just like a heat-only boiler, they have a separate hot water tank, except that it is unvented. 



Need to know the cost of a new boiler, quick? Find out what replacement you need along with costs (takes 60 seconds).

All parts such as the pump and expansion vessel are internal too, which also means it does not require a cold-water cistern tank and water is supplied to the boiler via the mains. 

Pros of system boilers 

System Boiler Pros

Just like heat only boilers, there large hot water storage cylinder means they are ideal for properties with high hot water demands.  

Since they have all their components internalised and do not require a cold-water cistern, it means that they do not require as much space as a heat-only boiler. It also means there is more flexibility with the installation location. 

System boilers do not require any components in the attic, it also means that you do not have to worry about any potential leaks or freezing during the winter months. 

Cons of system boilers 

System Boiler Cons

The hot water flow rate within the home largely depends on the pressure of the mains supply, so if t’s low, the flow rate within the home will be limited. For this reason, they are not ideal for places that suffer from low water pressure. 

The high-pressure nature of this system means that it may not be suitable for properties with older systems. 

System boilers need a hot water storage cylinder and so if you are swapping it for a combi boiler, you will need to find adequate storage space. 

System boiler key points: 

  • Recommended for properties with multiple bathrooms/hot water outlets. 
  • Does not require a cistern tank in the loft. 
  • Internal components make installation easier.  

  • May not be suitable for areas that suffer from low water pressure. 
  • May not be suitable for older central heating systems that cannot tolerate high water pressures. 
  • If you are swapping from a combi, you need to consider where you will store the hot water tank. 

Want to have your boiler moved to a different location? Check out our "cost of moving boiler" guide.

Boiler Type Frequently Asked Questions

Boiler Type FAQ's

Are you still curious about some aspect of choosing a new boiler? It’s not surprising for such a complex piece of engineering, here are some of the most frequently asked questions: 

What is a condensing boiler?

No matter what type of boiler you are thinking of having installed, the law says that it must be a condensing one.

All condensing boilers are at least 90% energy efficient, can harness excess energy to heat your home, are better for the environment and will help to reduce your heating bills.

Condensing isn't a 'type of boiler' as such, it's more of a technical attribute.

What size boiler do you need? 

When considering boiler size, it typically refers to the boiler’s power output and not the dimensions of the boiler. A boilers power is measured in kilowatts per hour (kWh), so put simply, the greater the kW, the greater the capacity of the boiler to meet your properties hot water and heating requirements. 


Want an exact price on a new boiler? Use our boiler quote calculator (no personal details needed).

Typically, boiler manufacturers will offer their boiler’s in a range of different sizes. Your boiler installer will determine what size you need from the number of radiators in your house. 

For instance, if you live in a small bungalow, then a small combi boiler is probably going to be recommended. However, if you live in a home with many rooms, all containing radiators, then a large-sized boiler will be required to meet the heating demands.  

Want to save money and energy on your heating bills? If so, you should consider installing one of the best smart thermostats.  

Types of Boilers Final Words 

The type of boiler that is most appropriate for your home will depend on a variety of factors, including your hot water demands, property size and available water pressure.  

With that said, the majority of UK homes use gas combi boilers, with regular and system boilers following behind. 

Whatever type of boiler you decide to install, you can buy any of them including installation via Heatable. 

Use this clickable form to get a fixed price on the screen instantly.

At Heatable, we fit new boilers from as little as £1,545, all over the UK.

What's more, as we've already covered, our boilers come with warranties which are up to 10 years long. That's loooooong.

What's even more, we're able to offer low monthly payments with boiler finance, and even interest-free options.

Get a fixed quote on a new boiler installation in 60 seconds, here.

More advice

New boiler deals

Buy your new boiler, better

Get a fixed price on a Which? Best Buy in minutes

Heatable is registered in England and Wales No. 08804726 (VAT No. GB205805920 ). Trading address is 1 Station Road, Great Sankey, Warrington, Cheshire, WA5 1RH. Heatable acts as a credit broker (not as a lender) and offers credit products through a panel of lenders. Heatable is authorised and regulated by the Financial Conduct Authority (reference no. 805259).

[1] Price based on a like for like combi swap in a 2 bed, 1 bathroom terraced home with a standard flue

[*] Installation dates are subject to installer availability

[ยน] only available on combi boiler installations

Financial Support: If you are in receipt of certain benefits, you may be entitled to claim a free boiler grant.