Cause of error code E18

Thermal Overrun Condition:
Outlet water temp. above 200 °F

Solution for error code E18

1. Check system for:
Verify boiler and system are full of water.
Make sure system does not have trapped air.
Inspect and verify system piping and components.
Make sure water flow is not reversed or pipes crossed.

2. Use contact thermometer to check outlet water temp. Compare to temp.
shown with display in “INFO” mode (“1” in first digit). Replace return temp. sensor if results are not close. Replace control module if sensor replacement doesn’t solve problem.