Both regular and system boilers store hot water in a cylinder, but they differ in their configuration::* **Regular boiler (conventional boiler):** The most traditional type of boiler system. It takes up considerable space due to the separate tanks..* **System boiler:** Stores hot water in a cylinder but has some key components built in, like the expansion vessel and pump. . This means it takes up less space and is easier to install than a regular boiler..The best choice depends on the size of your home and your hot water needs.