Navien Error Code E407: Dom.Hot Water Outlet Sensor
How to Fix Navien Code E407
- Step 1: Turn the unit off and then back on again. This may clear a temporary error.
- Step 2: Check the wiring connections on the outside of the unit for obvious signs of damage or corrosion. Do not open the unit. If you see anything suspicious, call a technician.
- Step 3: If the error persists after restarting the unit, contact a qualified HVAC technician to diagnose and repair the problem.
How to Reset Navien Code E407
- Turn off the unit using the power button on the front panel.
- Turn off the gas supply valve.
- Turn off the circuit breaker supplying power to the unit. Wait 30 seconds.
- Restore power at the breaker, then open the gas valve.
- Turn the unit back on. If the error returns, the underlying issue needs repair.
Resetting clears the code from the display but does not fix the underlying fault. If the code returns after reset, proceed to the diagnostic steps above.
What Does Navien Error Code E407 Mean?
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.
Common Causes
- Faulty DHW outlet temperature sensor
- Loose or corroded wiring connections to the sensor or the main control board
- Wiring harness damage (rodent damage, physical stress)
- Main control board failure (less common, but possible)
- Scale buildup on the sensor, insulating it from the water temperature
Diagnostic Steps
| If... | Check | Expected |
|---|---|---|
| Unit displays E407 error | Measure resistance across the DHW outlet temperature sensor terminals at the main control board with the unit powered off and sensor disconnected. | Resistance should match the temperature/resistance chart in the Navien service manual. Typically around 10-12 kOhms at room temperature (25°C). |
| Sensor resistance is out of range or open circuit | Inspect wiring harness and connections between the sensor and the main control board for continuity and shorts. | No breaks or shorts in the wiring. |
| Wiring is intact | Check voltage at the sensor connector on the main control board with the unit powered on. | Typically 5 VDC. Refer to the Navien service manual for the exact voltage. |
| Voltage is present at the board, wiring is good, and sensor resistance is in range | Suspect a faulty main control board. | Replace the main control board and re-test. |
Applicable Navien Models
Source Documentation
Referenced in 2 official Navien technical manuals.
| Manual | Page | Reason | Action |
|---|---|---|---|
| Navien NCB-H Installation & Operation Manual | 129 | Dom.Hot Water Outlet Sensor | Contact technical support at 1-800-519-8794. |
| Navien NFC-H Installation & Operation Manual | 127 | Hot water outlet: thermistor open or short circuit | Auto RESET |
Recall Notices
Issued: December 20, 2018
Affected models: NPE-180A, NPE-180S, NCB-180E manufactured July 9 - October 14, 2018
LP gas conversion kits can cause units to produce excessive carbon monoxide.
Replacement Parts
| Part | OEM Number | Est. Cost | Where to Buy |
|---|---|---|---|
| DHW Outlet Temperature Sensor | 30012345A | — | Find Part |
| Main Control Board | 30008721B | — | Find Part |
| Wiring Harness | — | — | — |
Related Codes on Same Models
Other codes that affect the same Navien model families as E407.
| Code | Description | Severity |
|---|---|---|
| E001 | Ignition Failure | Warning |
| E003 | Abnormal Ignition | Warning |
| E004 | False Flame Detection | Warning |
| E012 | Flame Loss | Warning |
| E016 | Overheating | Warning |
| E030 | Exhaust Overheat Sensor | Warning |
| E031 | Inlet Thermistor Open/Short | Warning |
| E046 | Outlet Thermistor Open/Short | Warning |
| E047 | DHW Thermistor Open/Short | Warning |
| E060 | Fan Motor Abnormality | Warning |