A combi boiler (combination boiler) provides both central heating and domestic hot water on demand, directly from the mains water supply. Unlike conventional boiler systems, a combi boiler doesn't require a separate hot water cylinder or a cold water storage tank in the loft, which makes them compact and ideal for properties where space is limited. Combi boilers are very popular in flats and houses with less hot water requirements since they deliver hot water instantly to taps and showers. Combi boilers are a good option for properties with one or two bathrooms.