Navien Error Code E278: Mixing Valve Stuck
Warning: Your Navien boiler has detected a stuck mixing valve, which could lead to system damage if not addressed.
How to Fix Navien Code E278
- Check your boiler's water pressure gauge. If it's above 30 PSI, you may need to bleed the system to reduce pressure.
- If you're comfortable doing so, you can try powering down the boiler and manually turning the mixing valve handle to see if it moves freely. If not, it's time to call a professional.
- Always call a professional HVAC technician if you're unsure about any part of the process or if the error code persists after attempting these steps.
How to Reset Navien Code E278
- 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 E278 Mean?
The E278 error on your Navien boiler indicates that the mixing valve is stuck in one position, either fully open or fully closed. This valve is responsible for regulating the temperature of the water in your boiler. When stuck, it can't adjust the water temperature properly, leading to inefficient heating and potential system damage. This issue is common in Navien boilers due to mineral buildup or debris in the valve.
Common Causes
- Mineral buildup or debris in the mixing valve
- Wear and tear on the valve's internal components
- Incorrect water pressure
- Faulty valve motor or solenoid
Diagnostic Steps
| If... | Check | Expected |
|---|---|---|
| Boiler is not heating | Measure the water temperature at the boiler's inlet and outlet. Also, check the mixing valve's position. | Inlet temperature should be higher than outlet, and the valve should be in the middle position. |
| Boiler is overheating | Check the mixing valve's position and measure the water temperature at the boiler's inlet and outlet. | Valve should be in the middle position, and outlet temperature should be lower than inlet. |
Applicable Navien Models
Source Documentation
Referenced in 5 official Navien technical manuals.
| Manual | Page | Reason | Action |
|---|---|---|---|
| NFB-H Installation & Operation Manual | 116 | Ext. Supply Sensor Not Detected | Check sensor connections. |
| Navien NCB-H Installation & Operation Manual | 129 | Ext. Supply Sensor Not Detected | Contact technical support at 1-800-519-8794. |
| Navien NFB-H Installation & Operation Manual | 116 | Ext. Supply Sensor Not Detected | Check sensor connections. |
| Navien NFC-H Installation & Operation Manual | 127 | Abnormal operation: system supply thermistor | Alarm |
| Navien NHB-H Installation & Operation Manual | 119 | Ext. Supply Sensor Not Detected | Check sensor connections. |
Replacement Parts
| Part | OEM Number | Est. Cost | Where to Buy |
|---|---|---|---|
| Mixing Valve | NAVIEN 102012000 | — | Find Part |
| Solenoid Valve | NAVIEN 102012001 | — | Find Part |
Related Codes on Same Models
Other codes that affect the same Navien model families as E278.
| 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 |