Category - Boilers
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Will Scholfield, Engineer

31 Jan : Updated 17 May ● 7 min read

What is a system boiler?

Most households rely on their boiler to give them heat when they need it, whether this is in the form of hot water or central heating. There are so many choices in terms of boilers that it can be difficult to decide which is the right one for you and your home. These are the main terms you may have come across in your search:

In this guide, we’ll focus on the system boiler. What is a system boiler and how do they work? How do they compare to the other different boiler types?

What is a system boiler?

This type of boiler works similarly to a regular standard boiler. It heats your central heating system by producing hot water for a storage cylinder. However, unlike standard boilers, the water supply is taken directly from the water mains.

How does a system boiler work? Cold water from the mains enters the boiler first. The heat exchanger will heat up the water and as it heats up, the water is then transferred into the hot water cylinder. Here is where it will stay until it is required. Because there is a larger amount of hot water available, multiple taps or showers can be used at once - a steady supply of hot water is readily available.

A system boiler has a separate hot water storage cylinder so, naturally, it can sometimes be difficult to tell the difference between this type of boiler and a regular standard boiler. Although, it’s important to remember that a system boiler only requires a boiler and a cylinder. Your regular standard boiler needs header tanks in a loft space to provide hot water to the cylinder and to keep the water in radiators to a sufficient level.

This reason alone means that system boilers are the go-to choice when deciding between this type and the traditional type. A regular boiler may be more suitable for those with different needs, such as homes with older radiators or those areas with a low water pressure.

What do you need to consider?


    As with any new boiler system, you need to consider the factors that may prevent you from having one. The main issue is space.

    If you have a lot of cupboard space available in your home or even an airing cupboard tucked away that you don’t use regularly - then this can be the perfect place to have your hot water cylinder. Something so bulky is best hidden out of the way, so if you’re struggling with space, maybe a different type of boiler system would be better suited to you and your household. However, a system boiler is great for homes without a loft space or with a loft conversion as a header tank is not needed.


    Boilers these days are very efficient. However, it’s worth noting the fact that with a system boiler, you will lose some heat from the hot water cylinder itself. To help prevent this from happening, it’s important to correctly insulate your cylinder to stop that excess heat from escaping.

    System boilers are really efficient at providing almost instant hot water for your showers and taps and due to this, it’ll be much easier to help control the water consumption in your home. There is a limitation of hot water you can store because of the cylinder’s capacity, so if you want more hot water after you’ve emptied the cylinder, you’ll have to wait for it to be heated up.

    It’s important to make a note of how much water you use to determine whether a system boiler would make for a more efficient boiler for you.

    What are the advantages of system boilers?

    System boilers come with a long list of advantages to ensure you have the best experience.

    Easy installation.

    Boiler installation of a system boiler is much quicker and easier than a regular boiler. A lot of the heating and hot water components are built into the system, meaning that it can be more compact; you’re not having to install anything into the loft space, taking up much less room.

    Hot water on demand.

    Your system boiler’s water tank means that you’ll have hot water in an instant. You can use multiple taps or have more than one shower running at once without any water pressure reduction. Bigger households can really benefit from this as well as homes with more than one bathroom.


    Even though the heat cylinder will lose heat if not properly insulated, a system boiler is quick to respond to your needs and has lower running costs than some other types. Look at the different types of insulation for your water tank and you’ll be making your system much more economic in the process.

    Strong water pressure.

    With a system boiler, you’ll have a mains water supply, so the water coming out of taps and showers will be high in pressure compared to a regular boiler. As already mentioned, you’ll not notice a difference if multiple taps or showers are being used at once.

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    How to convert system boiler to combi

    If you currently have a system boiler set up in your home and you’re not sure it’s working for you, it may be the right time to make the switch. However, it may also seem daunting. You may have lived with your current setup for so long that you’re comfortable with the way things are running and may not want the hassle of changing. Everyone feels like that, but in fact, switching could save you a lot of time, money and energy in the long run.

    Converting to a combi boiler from a system boiler, or another type of setup may sometimes be worth it – it completely depends on your needs. If you could do with the space and you have a regular boiler with a water tank in the loft, then switching would be an advantage.

    When you’re settled on the decision to switch from your system boiler to a combi boiler, you should firstly compare boiler prices and get a quote. Getting a price from our team is hassle free and will give you an estimate of boiler and installation costs. If you need to talk to someone about your options, you can always speak with an expert through our web chat feature to ask any questions.

    To be able to convey your boiler needs to an expert for their opinion, it’s worth working out your water and heating patterns and the amount of water you think you use. A heating expert will ask you questions in order to pick out the right boiler system for you. If you’re not sure, an expert will try and estimate this based on the information you tell them. When you have agreed an installation date and the time comes around, here are some of the things a professional will do on installation:

    • The existing heating and hot water system will be drained and the old or existing boiler and tanks will be removed, along with any controls/thermostat.
    • Your system will be converted to combi which can sometimes take an extra day depending on what your current system is.
    • The new combi boiler and filters will be installed and a chemical flush will be performed on the whole system.
    • Smart wireless thermostats will be installed and configured to the new boiler.

    Depending on the type of boiler you have currently, changing boiler types, especially to a combi boiler, can be quite difficult and time consuming. Only those engineers who are Gas Safe Registered should do a job like this, so don’t try and do it yourself! Costs can vary, so get in touch with our team for a quote.

    What is a system boiler? It could be an efficient and space-saving setup.

    It’s important to talk to the right engineers before making any decisions on the future of your heating set up. An expert can help you to determine which new boiler is the perfect fit for your home. If you’re wondering whether a system boiler is the one for your household or if you’d like an expert’s opinion or advice on any other boiler type, contact our engineers today through our website’s live chat feature.

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