A combi boiler is a type of heating system that provides both hot water and central heating from a single unit. It heats water directly from the mains supply, which means there is no need for a separate hot water tank. This makes it a space-saving option, ideal for smaller homes. Combi boilers are efficient because they only heat water when needed, reducing energy waste. They are popular in many countries due to their convenience and lower installation costs compared to traditional systems that require separate components for heating and hot water.