Navien Error Code E407: Dom.Hot Water Outlet Sensor

The E407 error code on your Navien tankless water heater indicates a problem with the domestic hot water (DHW) outlet temperature sensor. This sensor is responsible for monitoring the temperature of the hot water as it leaves the unit and goes to your faucets. The Navien's control board uses this temperature reading to modulate the burner and maintain a consistent hot water temperature. If the sensor is faulty, disconnected, or reading an implausible value, the unit will shut down and display the E407 error to prevent overheating or other issues. Basically, the Navien doesn't know how hot the water is, so it's playing it safe by shutting down. This error can stem from a few different issues, ranging from a simple wiring problem to a failing sensor. Because the Navien relies on accurate temperature readings to operate safely and efficiently, it's important to address this error promptly. While some basic troubleshooting can be done, this error usually requires a qualified technician to diagnose and repair.