Stiebel Eltron tankless heater shows E03 and shuts down; water may briefly get hot then unit stops.

Safety: Switch off the circuit breaker and close the cold water supply before opening the unit.

• Access the inlet NTC: Remove the front cover. The inlet sensor is mounted on or near the cold water inlet pipe.
• Check mounting and cleanliness: Ensure the sensor is firmly attached to the pipe and not hanging loose. Clean any scale or corrosion from the contact area so the sensor can read accurately.
• Inspect wiring: Follow the sensor wires to the control board. Confirm the connector is fully seated and that there are no cuts or burn marks on the insulation.
• Resistance check (optional): With power off, disconnect the sensor and measure its resistance. Compare to the manufacturer’s NTC curve. Replace the sensor if readings are far outside spec or open/shorted.
• Reassemble and reset: Reconnect everything, restore water and power, and clear the error by cycling power. If E03 reappears, replace the inlet NTC sensor. Persistent errors after sensor replacement may indicate a faulty control board.