E08 error, unit shuts down; may occur during domestic hot water draw or high load conditions.

Safety: Turn off power and close the cold water supply to the water heater if you will be opening any water connections.

• 1. Locate DHW sensor: On Triangle Tube indirect or combi water heaters, the DHW sensor is typically inserted into a well on the storage tank or plate heat exchanger outlet.
• 2. Inspect wiring: Check the DHW sensor cable for damage and ensure the connector at the control board is fully seated.
• 3. Check for scale or sludge: If the sensor is in a well, heavy scale or sludge can insulate it. If accessible, remove the sensor and inspect the well. Flush or clean according to manufacturer instructions.
• 4. Test sensor resistance: With power off and sensor disconnected, measure resistance and compare to the Triangle Tube chart. Replace if readings are open, shorted, or far off expected values.
• 5. Replace DHW sensor: Install a new OEM DHW NTC sensor, using thermal paste if specified. Ensure watertight reassembly.
• 6. Restore service: Turn water and power back on, purge air from hot water lines, and verify stable DHW temperature without E08 returning.