System Boilers
A system boiler is the term for a heat-only boiler. System boilers are a type of condensing boiler which occupy the middle ground between combi boilers and the regular boilers.
Unlike combi boilers, both system boilers work on the principle of storing hot water in a copper cylinder (usually in the airing cupboard). A system boiler will provide heating together with the power to heat water to be stored within the cylinder as part of a sealed system. Notwithstanding this system boilers differ from regular boilers in some fundamental respects.
The key difference with a system boiler is that all the major components are built in to the boiler. By building in components, which most other boilers situate outside the unit, system boilers can provide a compact and attractive installation. One noticeable difference is that a feed and expansion tank in the attic is no longer needed.