Display shows E04 and the water heater shuts down; unit may have overheated, hot water stops abruptly.

Safety: Allow the heater to cool completely before opening the casing. Turn OFF power and gas.

• Reset overheat stat (if manual reset type): Some Termet models have a manual reset overheat thermostat on the heat exchanger. Press the small red or black reset button if present.
• Check water flow: Ensure inlet filters and strainers are clean. Low flow can cause overheating. Clean the cold water inlet filter on the Termet hydraulic block.
• Descale heat exchanger: If the unit is in a hard water area, scale may block the heat exchanger. Disconnect the heater from power and water, then use a pump and descaling solution to flush the Termet heat exchanger according to the service manual.
• Inspect NTC sensor: Check the wiring to the flow and outlet NTC sensors. Replace the sensor if its resistance is out of specification (refer to Termet technical data).
• Call a technician: If E04 recurs frequently, a professional should check combustion, gas rate, and perform a full descaling or replace the overheat thermostat.