E278 🟡 Repair Required
Navien Error Code E278: Mixing Valve Stuck
⚠️ 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.
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 of Navien Code E278
- 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
Applicable Navien Models
Source Documentation
This error code is documented in 5 official Navien technical manuals.
NFB-H Installation & Operation ManualPage 116
ReasonExt. Supply Sensor Not Detected
ActionCheck sensor connections.
Navien NCB-H Installation & Operation ManualPage 129
ReasonExt. Supply Sensor Not Detected
ActionContact technical support at 1-800-519-8794.
Navien NFB-H Installation & Operation ManualPage 116
ReasonExt. Supply Sensor Not Detected
ActionCheck sensor connections.
Navien NFC-H Installation & Operation ManualPage 127
ReasonAbnormal operation: system supply thermistor
ActionAlarm
Navien NHB-H Installation & Operation ManualPage 119
ReasonExt. Supply Sensor Not Detected
ActionCheck sensor connections.
Need a Pro to Fix Navien Code E278?
A licensed HVAC technician can diagnose and fix this issue quickly.
Find a Licensed Tech Near You →Replacement Parts for Navien Tankless Water Heater Code E278
Mixing Valve OEM: NAVIEN 102012000
Solenoid Valve OEM: NAVIEN 102012001