Navien Error Code E445: Abnormal Mixing Valve
How to Fix Navien Code E445
- Step 1: Power cycle the unit. Turn off the power to the Navien at the breaker for 30 seconds, then turn it back on. This may clear a temporary glitch.
- Step 2: Check the water pressure. Ensure that both the hot and cold water supply pressures are within the recommended range for your Navien model (typically 20-80 PSI). Low pressure can affect the mixing valve's operation.
- Step 3: If the error persists after these steps, contact a qualified HVAC technician to diagnose and repair the issue.
How to Reset Navien Code E445
- 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 E445 Mean?
The E445 error code on your Navien tankless water heater indicates an issue with the mixing valve. This valve is responsible for blending hot and cold water to achieve your desired output temperature. When the system detects an abnormal condition within the mixing valve's operation, such as a failure to reach the target temperature or erratic behavior, it triggers the E445 error and shuts down the unit as a safety measure. This prevents you from getting scalding hot water or, conversely, no hot water at all. It's important to address this promptly to restore consistent hot water supply and prevent potential damage to other components.
Common Causes
- Mixing valve failure: The valve itself may be faulty due to wear and tear, scale buildup, or internal component failure.
- Faulty mixing valve actuator: The actuator motor that controls the valve's position may be malfunctioning.
- Wiring or connection issues: Loose or damaged wiring between the mixing valve and the main control board can cause communication problems.
- Software Glitch: A rare software glitch in the Navien's control board could cause a false error reading.
Diagnostic Steps
| If... | Check | Expected |
|---|---|---|
| Mixing valve is not moving or is stuck | Measure the voltage to the mixing valve actuator while the unit is calling for hot water. | Expect to see 24V AC. No voltage indicates a wiring or control board issue. Continuous voltage even when not calling for heat indicates a faulty control board or actuator. |
| Actuator receives proper voltage | Check the resistance of the mixing valve actuator motor windings. | Refer to the Navien service manual for the specific resistance range for your model. An open or shorted winding indicates a faulty actuator. |
| Wiring and actuator test good | Manually move the mixing valve. It should move freely. Check for scale buildup or debris obstructing the valve's movement. | Valve should move smoothly. If restricted, clean or replace the valve. |
Applicable Navien Models
Source Documentation
Referenced in 2 official Navien technical manuals.
| Manual | Page | Reason | Action |
|---|---|---|---|
| Navien NCB-H Installation & Operation Manual | 129 | Abnormal Mixing Valve | Contact technical support at 1-800-519-8794. |
| Navien NFC-H Installation & Operation Manual | 127 | Abnormal operation: Bypass mixing valve | Alarm |
Replacement Parts
| Part | OEM Number | Est. Cost | Where to Buy |
|---|---|---|---|
| Mixing Valve Assembly | 30012699A | — | Find Part |
| Mixing Valve Actuator | — | — | — |
Related Codes on Same Models
Other codes that affect the same Navien model families as E445.
| 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 |