Navien Error Code E046: Outlet Thermistor Open/Short

The E046 code on your Navien unit means the outlet thermistor, a temperature sensor located on the hot water outlet pipe, is either open (infinite resistance) or shorted (near-zero resistance). This sensor tells the control board how hot the water leaving the heat exchanger is. When it fails, the board can't regulate the burner properly, so it shuts down the system to prevent overheating or damage. This is a common issue on Navien combi boilers and water heaters, especially after several years of use. For a homeowner, you'll likely see this error after the unit runs for a minute or two and then stops. The display will flash E046, and the unit will not heat water or run the central heating until it's fixed. The thermistor is a sensor mounted on the outlet pipe, often behind the front panel. While no gas or water leaks are associated with this code, you need a professional to replace the sensor to get your system back online. The fix requires removing the front cover, unclipping the sensor from the pipe, and installing a new one. Most homeowners should call a pro, but if you're handy, you can buy the right thermistor from a Navien supplier. Just be aware that mishandling the wiring can cause other issues.