Navien Error Code E279: Mixing Valve Open Failure
Warning: Your Navien boiler has detected a failure in the mixing valve, which could lead to system damage if not addressed.
How to Fix Navien Code E279
- Step 1: Check if your boiler is receiving power. If not, reset the power by turning off the breaker for a few minutes and then turning it back on.
- Step 2: Inspect the mixing valve for any visible damage or leaks. If you find any, do not attempt to fix it yourself and call a professional immediately.
- Step 3: If the problem persists, call a licensed HVAC technician to diagnose and repair the issue.
How to Reset Navien Code E279
- 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 E279 Mean?
The E279 error on your Navien boiler indicates a problem with the mixing valve's open circuit. The mixing valve is responsible for blending the hot water from the boiler with the cold water coming into your home. If it's not opening correctly, your boiler can't provide hot water, and you might notice a lack of hot water or reduced water temperature. This issue is typically caused by a faulty valve or a problem with the wiring or control board connected to it.
Common Causes
- Faulty mixing valve
- Wiring issue between the mixing valve and control board
- Problem with the control board itself
Diagnostic Steps
| If... | Check | Expected |
|---|---|---|
| Boiler is not providing hot water | Measure the voltage at the mixing valve's control wire using a multimeter | 12-24V AC (depending on your boiler model) |
| Voltage is present but boiler still not functioning | Inspect the mixing valve for any signs of physical damage or leaks | No visible damage or leaks |
Applicable Navien Models
Source Documentation
Referenced in 5 official Navien technical manuals.
| Manual | Page | Reason | Action |
|---|---|---|---|
| NFB-H Installation & Operation Manual | 116 | Ext. Return Sensor Not Detected | Check sensor connections. |
| Navien NCB-H Installation & Operation Manual | 129 | Ext. Return Sensor Not Detected | Contact technical support at 1-800-519-8794. |
| Navien NFB-H Installation & Operation Manual | 116 | Ext. Return Sensor Not Detected | Check sensor connections. |
| Navien NFC-H Installation & Operation Manual | 127 | Abnormal operation: system return thermistor | Alarm |
| Navien NHB-H Installation & Operation Manual | 119 | Ext. Return Sensor Not Detected | Check sensor connections. |
Replacement Parts
| Part | OEM Number | Est. Cost | Where to Buy |
|---|---|---|---|
| Mixing Valve | 3201100010 | — | Find Part |
| Control Board | 3201200010 | — | Find Part |
Related Codes on Same Models
Other codes that affect the same Navien model families as E279.
| 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 |