The control system has detected that the flame sensor is grounded.
Disconnect the wire from the flame sensor (see pages 12 and 24). Check for continuity between flame sensor and ground with an ohm meter. There should be no continuity – infinite resistance.
If above test indicates there is continuity between the flame sensor and ground – remove the flame sensor (see pages 12 and 24). Ensure the flame sensor is not bent and touching the burner.
Check all flame sensor wiring between the flame sensor and the J4 male spade connector on the CCB (page 36). Ensure there are not any pinched wires or shorts – repair/replace anything worn or damaged. Replace the flame sensor.
Call the technical support phone number shown on the water heater labeling for further assistance if the problem has not been corrected after performing the procedures outlined here.