How often do you need to flush a Navien tankless water heater?

How often you need to flush a Navien tankless water heater is typically once a year, or every 6 months if you have hard water, which is standard for tankless water heaters to prevent scale buildup and maintain efficiency. Navien was founded in 1978 in South Korea, headquartered in Seoul, South Korea, makes Navien tankless water heaters with stainless steel heat exchangers that can accumulate calcium and magnesium scale from hard water, reducing efficiency and lifespan. Navien recommends flushing tankless water heater once a year for soft to moderate water hardness, and every 6 months for hard water over 7 grains per gallon, using white vinegar or descaling solution pumped through unit with isolation valves. Flushing involves turning off power and gas, closing water valves, connecting pump to circulate vinegar for 45 minutes, then rinsing. Annual flushing costs $100 to $200 if done by professional, or $20 DIY. Neglecting flushing causes error codes, reduced flow, and shorter lifespan from 20 years to 12 to 15 years. Navien has built-in scale detection that alerts when flushing needed. So flush Navien tankless once a year for normal water, every 6 months for hard water, to maintain efficiency, prevent scale, and extend lifespan to 20 plus years, with regular maintenance including cleaning inlet filter.