Method for preventing coagulation in exhaust pipe of boiler

A method and an apparatus are provided for preventing coagulation in an exhaust pipe of a boiler is provided. The method includes operating the boiler and executing a combustion stroke, determining if an ambient air temperature measured by an ambient air temperature detecting sensor is equal to or lower than a first temperature, shifting a 3-way valve to a hot-water location if the measured ambient air temperature is equal to or lower than the first temperature, executing an extinction stroke of a burner if the temperature of space heating water reaches a second temperature, and operating a circulation pump and a blower to exchange heat in a heat exchanger and to discharge warm air through an exhaust pipe, thereby preventing coagulation in the exhaust pipe of the boiler.