E12 displayed; heater works intermittently and unit may shut off heating unexpectedly.

Safety first: Unplug and allow the heater to cool before touching any heater components.

• Locate the NTC sensor: Find the small probe or clip-on sensor attached to the heater block or solution line.
• Check attachment: Ensure the sensor is firmly in contact with the heater surface or properly inserted into its well.
• Inspect wiring: Follow the sensor wires to the PCB, checking for cuts, pinches, or loose connectors.
• Test the sensor: Use a multimeter to measure resistance at room temperature and compare with service specifications. An open or near-zero reading indicates a faulty sensor.
• Replace NTC if defective: Remove the old sensor, install the new one in the same position, secure it, and reconnect wiring.