Also known as combination boilers, combi boilers are single units which eliminate the need for a cold water storage tank or a hot water cylinder. Instead, the water is pumped directly from the mains into the boiler and heated on demand, serving both your central heating system and your hot water taps and showerheads.
Because everything is contained within one unit, a combi boiler is far more space-efficient than some other alternatives. It’s also more energy-efficient, since you only ever heat the water that you use. This has made it the most popular option in the UK, especially in smaller homes and apartments. On the other hand, it’s not ideal for properties with many bathrooms and occupants, since it does not excel at accommodating multiple users at the same time.
Like combi boilers, system boilers draw their water straight from the mains supply. However, unlike combi boilers, they require a hot water cylinder to store the water they heat. This means that they are an ideal choice for properties with greater hot water needs, since there will always be enough stored hot water available for all.
While the presence of a hot water cylinder does make them slightly less space- and energy-efficient than a combi boiler, they do not require a cold water storage tank. What’s more, the fact that most of the components of the heating system are housed within the boiler unit makes them straightforward to install, while their compatibility with solar power panels is another draw for environmentally conscious consumers.