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.
What does 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.