Warning: Your Navien tankless water heater has detected an issue with the return water temperature sensor and has locked out for safety. This will prevent hot water until the issue is resolved.
How to Fix Navien Code E818
Step 1: Check that the cold water supply to the unit is fully open.
Step 2: If it's very cold outside, and you've only been using small amounts of hot water, try running a hot water faucet at a moderate flow for a few minutes to see if the error clears. This might warm the return line enough for the unit to restart.
Step 3: If the error persists, contact a qualified HVAC technician to diagnose and repair the issue.
How to Reset Navien Code E818
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 E818 mean?
The E818 error code on your Navien tankless water heater indicates that the return water temperature sensor is reporting an abnormally low temperature. This sensor monitors the temperature of the water returning to the unit after it has circulated through your plumbing. If the return water is too cold, it can cause condensation inside the unit, which can lead to corrosion and damage. To prevent this, the unit shuts down and displays the E818 error. This is a protective measure to prevent damage to the unit. The sensor itself, the wiring, or the main control board could be at fault. It's important to address this issue promptly to avoid further problems and restore hot water service.