Heater shows E05, water temperature fluctuates or unit shuts down shortly after ignition.

Safety: Isolate power before testing sensors. Water in the system may be hot.

• Locate flow NTC: On Termet water heaters, the flow NTC is usually clipped to the outlet pipe or inserted into a sensor pocket near the heat exchanger outlet.
• Check connections: Inspect the NTC plug and wiring for damage or corrosion. Reseat the connector firmly on the PCB and at the sensor.
• Measure resistance: Disconnect the NTC and measure its resistance with a multimeter. Compare with Termet's temperature/resistance chart. A reading of near 0 Ω (short) or infinite (open) indicates a faulty sensor.
• Replace NTC: If faulty, drain the heater if necessary, remove the old sensor, apply thermal paste if specified, and install the new Termet NTC sensor.
• Control board: If the sensor tests good but E05 persists, the PCB input may be defective and the main control board may need replacement by a technician.