What is the working principle of a multi-point water heater or combination boiler?

A multi-point water heater or combination boiler operates on the principle of heating water on demand. This means that when a faucet or draw-off point is opened, the unit activates and heats water instantly as it flows through the system. This design eliminates the need for storing large quantities of hot water, making it efficient for household use.

In contrast, options that mention storing hot water or requiring an external hot water tank refer to traditional storage water heaters that accumulate hot water for later use, which is not the case with a combination boiler. The option stating that the unit heats water using electricity only is also inaccurate, as many combination boilers are powered by gas and are designed for immediate hot water delivery rather than relying solely on electricity. Thus, the correct choice emphasizes the on-demand heating capability that characterizes multi-point water heaters and combination boilers.