Display shows E03 and heater does not operate; may occur after a power surge or wiring work.

Safety: Switch off power at the main breaker. Confirm with a tester that no voltage is present.

• 1. Locate inlet NTC: Remove the front cover. Find the inlet temperature sensor on the cold-water inlet pipe or heat exchanger block.
• 2. Check mounting: Ensure the sensor is properly inserted into its pocket and secured. A loose sensor can give false readings.
• 3. Inspect wiring and connectors: Trace the cable to the control board. Look for cuts, crushed insulation, or signs of overheating. Reseat the connector on the PCB.
• 4. Resistance test: Disconnect the sensor and measure its resistance at room temperature. Compare to the Kospel specification. Replace the inlet NTC if readings are out of range or unstable.
• 5. Verify correct sensor placement: On some models, inlet and outlet NTCs are similar. Ensure they are not swapped. Refer to the wiring diagram on the inside of the cover.
• 6. Control board: If a new sensor and good wiring still result in E03, the main control board may be faulty and should be replaced by a qualified technician.