• Blog
  • Combi vs System Boilers

  • Blog
  • Combi vs System Boilers

    Updated: February 17, 2024

    Choosing the right boiler for your home can be a tricky matter. The decision is not easy for sure because you will have to stick with your choice for several years. 

    To put it simply, one of the main differences between a combi and a system boiler is that a combi boiler does not require a hot water cylinder for storing hot water. So unlike a system boiler, a combi boiler can save you some space. 

    On the other hand, system boilers are more suited for homes with high water demand and homes with multiple bathrooms. 

    Sometimes the choice is easier to make. If you already have a combi boiler and it is enough for your home, then you can easily just replace your old one with a new one. And the same thing applies if you have a system boiler.

    What is the difference between a combi and a system boiler?

    A combi boiler is a compact unit that can provide hot water for heating and use. It takes water from the mains and has the ability to heat water on demand whenever a tap or a shower is turned on. So a combi boiler eliminates the need for a hot water cylinder. 

    A combi boiler can be cost effective because there will be no need to pre-heat the water. 

    System boilers take water directly from the mains supply. This water is then heated by the heat exchanger which can transfer energy from gas to water. After that, the hot water is transferred to a storage cylinder ready to be used. 

    So a system boiler does nor require a cold water tank but it does require a hot water cylinder. System boilers can meet high water demand and are perfect for large homes with multiple bathrooms.

    Read Also : Different Types Of Reliable Boiler Systems Explained 

    What are the advantages of combi boilers?

    How water on demand 

    Combi boilers are great when it comes to providing hot water on demand. On the other hand, system boilers have to heat the water first and then store it. 


    Combi boilers are quite efficient. They have an efficiency rate of at least 92%. As a result of this, your energy bills will be lower and it can also reduce your carbon footprint. 

    Compact in size

    If you don’t have much space in your home, then a combination boiler is the perfect choice for you. Combi boilers are compact in size and don’t take up much space. They can even be fitted inside a kitchen cupboard.

    Easy installation 

    Combi boilers are very easy to install since they do not require either a cold water tank or a hot water cylinder. This will save you both time and money.

    Read Also : 10 Important Tips Before Buying A New Boiler In 2024

    Combi Vs System Boilers
    Combi Vs System Boilers 4

    What are the disadvantages of combi boilers?

    • Combi boilers can struggle with high water demand. Having multiple taps or showers on at the same time may lead to one of them to go cold. A combi boiler is not recommended when you have more than one bathroom. 
    • Combi boilers require high pressure water from the mains. If you live in an area with low water pressure, then the water coming from your taps will also be at low pressure. 
    • An old plumping network might not be able to cope with high pressure water flow from your combi boiler. So your home might require new pipes before getting a combi boiler. 

    What are the advantages of system boilers? 

    Can save up space

    A system boiler does not need a cold water tank and as a result can save you some space. 

    Good for large homes

    A system boiler can provide water to several taps and showers at the same time. In short, it can meet a high level of demand for hot water. 

    Compatible with solar panels 

    System boilers can be paired with solar panels if you are looking for a green way to generate power. 

    Hot water on demand 

    System boilers have a built-in pump that can deliver hot water on demand once you turn on a tap or a shower. 

    Can be more efficient 

    By using an electric immersion heater, your system boiler can be made more efficient and less reliant on gas.

    Read Also : Best Condensing Boilers | Combi Boiler Models

    What are the disadvantages of system boilers?

    • When you use all the hot water stored in the cylinder, you’ll need to wait for the boiler to heat some more.
    • System boilers need a hot water cylinder so if you don’t have enough space at your home they might be inconvenient for you. 
    • If you live in an area with low water pressure, a system boiler might not be the best choice. What is more, if you have old radiators, they might not be able to cope with the high water pressure of a system boiler. 
    • Due to having more parts than a combi boiler, a system boiler might require more maintenance. 

    Read Also :System & Best Boilers In Uk Of 2024

    Which boiler is the best? System or combi?

    This question cannot be simply answered by choosing one of the two. Each one of these two types has pros and cons. Your choice would depend on your heating requirements and the size of your home. 

    While a combi boiler might be more efficient than a system boiler, a system boiler can meet a high level of hot water demand and is best suited for larger homes. 

    Combi Vs System Boilers
    Combi Vs System Boilers 5

    When should I get a combi boiler?

    If you live in a flat by yourself, a combi boiler can be the perfect choice because it is both efficient and compact in size. 

    Even if you live in a three-bedroom house with one bathroom, a combi boiler might still be a good choice for you. 

    When should I get a system boiler?

    If you Live in a large house that has more than one bathroom, then you should definitely consider getting a system boiler. A system boiler can meet a high level of hot water demand.


    Is a combi boiler very efficient?

    Combi boilers are very efficient. They can show 92%-98% efficiency.

    Do combi boilers use gas or oil?

    Combi boilers can use different types of fuel. They can run on gas, oil, LPG (Liquified Petroleum Gas), and electricity.

    Are system boilers suitable for large homes?

    System boilers are very convenient in large homes with high demand for hot water. 

    Are system boilers efficient?

    Yes, they are. System boilers can reach an efficiency rate of 94%.