Tesy heater shows E05; water temperature reading on display is clearly wrong (e.g., shows 0°C or 99°C constantly).

Safety first: Isolate electrical power and allow the unit to cool if recently used.

Steps:

• Locate outlet sensor: On Tesy models with two sensors, the outlet or upper sensor is usually mounted near the hot water outlet or upper part of the tank. Follow the smaller sensor cable from the board.
• Check physical placement: Ensure the sensor is fully inserted into its pocket or clipped properly to the outlet pipe. A loose sensor can cause false readings.
• Inspect wiring: Look for cuts, abrasions, or melted insulation. Reseat the connector on the control board.
• Measure resistance: Disconnect the sensor and measure resistance at room temperature. Compare with the main NTC sensor value; they should be similar. If it reads open or short, replace it.
• Replace sensor: Install a new Tesy outlet NTC temperature sensor, ensuring correct seating and sealing of the sensor pocket.
• Test: Restore power and verify that the temperature reading is realistic and E05 is cleared.

Note: If both sensors read correctly but E05 persists, the control board’s sensor channel may be defective.