Heater display shows E10 and unit will not start

Safety first: Turn off power and stop the circulation pump before working on the plumbing or flow switch.

• Verify plumbing orientation: Confirm that water is entering and exiting the heater according to the arrows on the BWT unit. Incorrect plumbing can prevent the flow switch from closing.
• Inspect flow switch body: Locate the flow switch on the inlet line. Remove it if necessary (after draining pressure) and check for debris or scale preventing movement of the paddle or magnet. Clean gently.
• Check wiring: Inspect the flow switch cable and connector for damage or loose contacts. Reseat the connector at the control board.
• Test continuity (if skilled): With the pump running and power off to the heater, use a multimeter to verify that the flow switch closes (shows continuity) when water is flowing.
• Restart system: Reinstall the flow switch, restore power, start the pump, and then start the heater to see if E10 clears.

If E10 persists and flow is confirmed adequate, the flow switch is likely defective and should be replaced with a BWT-compatible part.