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  • System Boilers

    Updated: February 10, 2024

    What is a system boiler?

    Nowadays, people in the UK are advised to use a combi boiler for their hot water needs. But system boilers can, sometimes, be a better option for certain situations.

    Firstly, let’s take a look at what a system boiler means and see how they work. In addition to looking at some of the main reasons why a system boiler might be your best choice. Get a quote for a System Boiler Replacement without delay.

    The difference between system boiler and combi boilers

    To begin with, combi boilers have two functions. They provide you with hot water and they heat your home as well ,using a single unit. We recommend people who live in flats or homes with limited space to have a combi boiler. With a combi boiler, you wouldn’t have to worry about making space for the header tank or the hot water cylinder.

    However, combi boilers aren’t suitable for homes or flats with high hot water demand. What’s more, they are made to supply only one water outlet at a time. When there is need for hot water, your combi boiler would switch from heating to providing hot water. As a result, your central heating performance might be affected as well, as soon as you turn on your tap. Get a quote for a System Boiler Replacement without delay.

    On the other hand, a System boiler consists of a separate cylinder to store hot water. Hot water is kept in the cylinder despite the fact that the main heating and hot water system parts are put within the boiler. As a result, the hot water supply can support more than one taps and showers at the same time. That’s why a system boiler is the perfect option for homes with multiple bathrooms.

    What Is A System Boiler
    System Boilers 4

    The difference between system boiler and regular boilers

    The system boiler can be easily mistaken with the regular boiler (also known as a traditional or a conventional boiler) due to the separate hot water storage cylinder. However, there are some primary differences. Furthermore, a regular boiler might need a header tank to draw water from and to keep water levels in the radiator. While a system boiler is a sealed system that only has a cylinder.

    That’s why people sometimes prefer to go with a system boiler. Although in some cases a regular boiler can be more suitable to the needs of a certain household. Especially for those who live in areas with low water pressure or homes with old radiator systems which wouldn’t be suitable for high water pressure of a system boiler.

    The Advantages of System Boilers

    A large supply of hot water

    Generally, with a system boiler you can store large quantities of hot water to use later on. This is very useful when you are using multiple taps, showers and radiators at the same time.

    The ability to use solar energy.

    Without a doubt, connecting the correct cylinder to the system will enable you to use solar panels. This is not only environmentally friendly but it is also cost-effective and will save you some money.

    Needs less space than a regular boiler

    Of course, system boilers are easier to install and need less space than regular boilers. Moreover, they do not need an expansion tank or external expansion vessels

    Economical and fast

    Lastly, system boilers consist of a pump. As a result, they respond fast and have more economic running cost.

    Important things to consider in System Boiler

    There are also some drawbacks to installing a system boiler that you should keep in mind. Here are a few of them:

    System boilers need more space than combi boilers

    Although they take less space than regular boilers, they still require more space than combi boilers because of the external cylinder. Overall, this can be a huge problem in smaller homes when it comes to installations.

    Read more: New Boiler Cost

    Busier times means more patience

    Firstly, your cylinder will be sized in advance to cover your household need of water (usually 50 litres of hot water stored per person). However, in times when you have more visitors than usual and your use of hot water is doubled, your hot water storage may run dry. As a result, you will have to wait 30-40 minutes while your boiler is reheating the cylinder again.

    Read more: Electric Boilers v Gas Boilers

    What Is A System Boiler
    System Boilers 5

    Finding what you need

    In order to find the most suitable boiler for your home and needs you should take the time to compare different models. The question remains as to what to look for and what to compare.

    Output rate

    The output rate is the power of the boiler measured in kilowatts (kW). Because regular boilers consist of a central heating output rating, you will know how many radiators the unit is able of heating up.


    You can know the efficiency rating of a boiler from how much of the converted fuel is used to the maximum. Wthout a doubt, less energy is wasted when the efficiency rating is higher.

    Possible Cost

    To begin with, there are many options to choose from. Options that will suit your budget that is to say. The prices of a regular boiler can range from £500 to £2,000 (not including the cylinder and the installation cost).


    Boilers always come with a warranty by the manufacturer that will cover any problems that may happen after the installation. Each boiler has a different warranty that will cover certain things and not others. They also differ on the time they offer.

    Heating controls

    It’s important to have good heating control over your boiler in order to keep your energy use low. Now you can use your smartphone or tablets to control your boiler.

    Customer reviews

    Without a doubt, you would like your boiler to be reliable and to heat your home for years to come. Reading reviews left by homeowner is highly helpful. These kinds of feedbacks will make you familiar with certain problems and issues of certain boilers before buying your own.

    Engineer reviews

    Of course, heating engineers are experts in boilers. Their insight can help you find what kind of boiler you need. So always make sure to take the time to read what they have to say.

    Read more: Best Heat Only Boilers

    types of Gas Boilers

    The cost of installation

    A lot of factors can impact the cost of installation. These might be:


    Installation Complexity

    How much rates the installer would charge

    Your place of living (for instance, London can be more expensive).

    Generally speaking, having a boiler installation might cost you between £800 – £1,500. Here is an idea of how much it might cost you.

    Read more: Types Of Reliable Boiler Systems 

    ModelBoiler priceApproximate boiler price with installation
    Baxi 800£900 – £1,000£1,400 – £2,000
    Vaillant ecoTEC Plus£1,000 – £1,250£1,500 – £2,250
    Ideal Vogue Max£1,000 – £1,250£1,500 – £2,250
    Worcester Bosch Greenstar i£900 – £1,100£1,400 – £2,100
    Viessmann Vitodens 200-W          £1,250 – £1,500£1,750 – £2,500

    The right size for you

    When we talk about boiler size, we do not mean its dimensions, but rather its power output. The unit of measurement, used for system boilers, is the kilowatt (kW).

    To clarify, the higher the output of your boiler, the more powerful it will be. Nonetheless, it’s never a great idea to get the boiler with the highest output rating. A too high output rating would increase your energy bills. And a too low output rating will not meet your demand.

    Through counting the number of bathrooms and radiators in your home, you can find the most appropriate output rating. This nformation can also help you have an idea of the level of demand for domestic hot water and central heating.

    With this purpose in mind, we advise you to get a quote from a Gas Safe registered engineer. If you have a brand in mind, then you should check their website and guidelines. A lot of manufacturers, nowadays, offer advice on their websites.

     Here is a table to guide you through what you need to know:

    No. of bathroomsRadiatorsRecommended Output
    1109-15 kW
    2-31518-26 kW
    3+2027-40 kW

    To point out, small homes with one bathroom and little or no space for a cylinder should consider getting a combi boiler.

    Read about:

    Best Condensing Boilers

     Important Tips Before Buying A New Boiler


    Do system boilers run out of hot water?

    This factor is determined by the capacity of your hot water cylinder. You should consider how much water you need for taps, baths and showers when choosing the right size. However, you should keep in mind that the size of your cylinder will rely on the space available.

    How do system boilers function?

    Firstly, a heat exchanger heats the water. Then it moves energy from the gas jets to the water. Once the water is heated, it is moved to the hot water cylinder where it will be stored. Even when you are using multiple taps and showers, a constant supply of hot water is always available.

    How much space is required for a system boiler?

    There are many things to consider but one of the most crucial points is how much space do you need for a system boiler. In general, a system boiler is larger than a regular boiler so you need to make sure that you have sufficient space. What makes a system boiler bigger is the fact that it has a pump and an expansion tank.