Display shows E03 and the valve remains in one position; water flow may stop or stay in bypass.

Safety first: Disconnect power and close the inlet valve before removing the control head cover.

• Locate the position sensor: On Tier1 electronic valves, a small micro-switch or optical/rotary encoder is mounted near the cam/rotor. Note its wiring harness to the control board.
• Check mechanical alignment: Verify the cam or rotor disc is properly seated on the drive shaft and that the position switch actuator is correctly engaged. If the cam has slipped, realign it according to the service marks (e.g., HOME/SERVICE position).
• Inspect wiring: Ensure the sensor harness is fully plugged into the control board and not pinched or cut. Repair or replace damaged wiring.
• Test the switch/encoder: For a micro-switch, use a multimeter in continuity mode while manually rotating the cam; the switch should open and close as the cam moves. For an encoder, check for proper supply voltage from the board and signal changes (refer to Tier1 service data).
• Replace faulty components: If the switch or encoder does not change state, replace the valve position switch / encoder assembly. If a new sensor does not clear E03, the control board input circuit is likely defective and the board should be replaced.