Oso digital water heater displays E03 and does not heat; temperature reading seems incorrect or frozen.

Safety first: Turn OFF power at the breaker and confirm no voltage at the heater before removing covers.

• Locate the NTC sensor: On Oso cylinders, the tank sensor is usually inserted into a dry sensor pocket on the side of the cylinder or near the element boss, connected by a small two‑wire harness to the control board.
• Check the connection: Remove the front cover and inspect the sensor plug at the control board. Reseat the connector and look for corrosion or broken pins.
• Inspect the cable: Follow the sensor cable along the tank. Look for cuts, crushed insulation, or signs of rodent damage. Repair or replace damaged wiring.
• Test the sensor: Disconnect the sensor and measure its resistance with a multimeter. Compare to Oso’s temperature‑resistance chart (for example, many NTCs are ~10 kΩ at 25°C). If the reading is near 0 Ω (short) or OL (open), the sensor is faulty.
• Replace the sensor: Gently pull the sensor from the pocket, apply a small amount of thermal paste if recommended, and insert the new Oso‑specified NTC fully into the pocket. Route the cable neatly and secure it away from hot surfaces.
• Power up and test: Restore power and verify that the displayed temperature is realistic and that the E03 code clears.

If the sensor tests good but E03 remains, the control PCB may be defective and should be evaluated by a professional.