lets-do-diy.com logo lets-do-diy.com stripes
Account login  |  Register
Bookmark This Page

    System boilers

    Summary: System boiler (sealed boiler system) guide, advantages of a system boiler and disadvantages of a system boiler.

    System boilers

    A sealed (unvented) boiler system provides the central heating and hot water for a cylinder. The more familiar open vented system, commonly found in homes, uses two water tanks usually located in the loft, and a hot water storage cylinder positioned in the airing cupboard. The sealed system is similar, but uses less space in the loft as it requires one less storage tank. A cylinder will be needed in the airing cupboard as with the older styled system. People often replace the older open vented system with this sealed version.

     System Boilers - lets-do-diy.com


    • A system boiler differs from other types as many of the components that are required for heating and hot water are built into the system boiler meaning that installation is much easier, faster and neater.
    • The sealed system is increasing in popularity largely because of its space saving benefits. There isn’t a need for a feed or expansion cistern, so less space is taken up in the loft. This is extremely beneficial for smaller sized homes.
    • This type of boiler also has an excellent flow rate for domestic hot water (DHW), which means that the flow of hot water is not reduced in any way, as can be the case with other boiler systems. This makes it beneficial for larger properties that need a good water supply.
    • The system easily allows for more than one hot tap/shower to run simultaneously.


    • Unfortunately this type of boiler does not provide instant hot water. The water will need a little while to heat up.
    • If too much water is used too quickly, the storage cylinder will run out. This will mean that the user will have to wait for the water to resupply and heat up. This may take some time.
    • The hot water cylinder will need to be housed in some kind of airing cupboard. This takes up space, which may be undesirable.

    Return to top of page
    Discuss Project

    Join an existing conversation or create a new thread related to Plumbing and heating in our DIY forum.