Warning: Your Navien boiler has detected a header thermistor failure, which could lead to system damage if not addressed promptly.
How to Fix Navien Code E786
Step 1: Turn off your boiler at the main power switch to prevent further operation until the issue is resolved.
Step 2: Inspect the wiring harness connected to the header thermistor for any signs of damage or corrosion.
Step 3: If you're comfortable doing so, check the thermistor's resistance using a multimeter. A faulty thermistor will typically read either extremely high or low. If you're unsure about any of these steps, contact a professional HVAC technician.
How to Reset Navien Code E786
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 E786 mean?
The E786 error on your Navien boiler indicates a failure in the header thermistor, a sensor that monitors the temperature of the boiler's water jacket. This error is typically caused by a faulty thermistor or a poor electrical connection. If ignored, it could lead to overheating and potential damage to your boiler.
This error occurs when a different type of a front control panel is connected to the furnace. ● Check if the front control panel connected to the furnace is appropriate for the NPF Series furnace.