Heater shows A41; unit may not start or may shut down unexpectedly.

Safety: Disconnect electrical power and close the cold water supply to the heater. Relieve pressure by opening a hot water tap.

• Locate flow sensor: Remove the front cover. The flow sensor or flow switch is typically installed on the cold water inlet manifold.
• Clean inlet filter: Shut off the cold water isolation valve. Remove the inlet filter screen (if equipped) and rinse out debris. Reinstall securely.
• Inspect flow sensor: Remove the flow sensor body according to the manual. Check for scale, sand, or debris obstructing the turbine or paddle. Clean gently with water and a soft brush.
• Check microswitch (if mechanical): For mechanical flow switches, manually operate the paddle and verify the microswitch clicks and shows continuity with a multimeter.
• Check wiring: Inspect the harness from the sensor to the control board for damage. Ensure connectors are fully seated.
• Reassemble and test: Reinstall the sensor, open the water supply, check for leaks, restore power, and run hot water. Confirm that the A41 code clears and flow is detected correctly.