A System boiler directly heats your central heating system and produces hot water for a storage cylinder. They work like a Regular (Conventional) boiler in that they need to store hot water, but unlike Regular boilers they take their water supply directly from the mains.
System boilers require a cylinder for storing hot water, however the major heating and hot water system components are built into the boiler itself, making it quicker and easier to install. In addition, there is no need for a tank in the loft, so it can be an option in a home with little or no loft space or where the space is earmarked for a conversion.
These boilers are also compatible with solar water heating systems, which deliver environmental benefits as well as lower energy bills.