E09 displayed, unit may not respond to thermostat or control inputs correctly.

Safety: Shut off power and isolate the water heater from the system (close isolation valves) before removing any flow components.

• 1. Verify system flow: Ensure all isolation valves are open and that circulator pumps are operating. Low or no flow can cause the control to interpret a sensor fault.
• 2. Locate flow sensor/switch: On many Triangle Tube units, the flow sensor is installed on the cold inlet or system return line near the boiler connections.
• 3. Inspect wiring: Check the harness from the flow sensor to the control board. Reseat connectors and look for corrosion or broken wires.
• 4. Remove and clean sensor: Close valves, relieve pressure, and drain as needed. Remove the flow sensor body. Inspect for scale, sludge, or debris preventing the paddle or turbine from moving. Clean gently with a soft brush and rinse.
• 5. Check orientation: Confirm the arrow on the flow sensor body matches the direction of water flow. Incorrect installation can cause E09.
• 6. Reinstall and test: Reassemble, open valves, purge air, and restore power. Call for heat or hot water and verify that flow is detected and E09 clears.
• 7. Replace if necessary: If the sensor is physically damaged or still not recognized, replace it with the correct Triangle Tube flow sensor.