What are the differences between a regular boiler and a system boiler?

When it comes to relying on a hot water storage cylinder, then both systems are very similar. Both of them keep a store of hot water ready for your use. However, the main difference is that a system boiler draws water directly from the mains. While, a regular boiler will take its water supply from a tank in the attic. In short, with the system boiler you do not need a cold water tank high up in the attic.