E3 error and burner or elements cycle erratically, water temperature unstable

Safety first: Disconnect power and shut off gas. Allow the tank to cool completely; scalding water may be present.

• Access tank sensor: Remove the upper and/or lower access panels on the Giant heater. Locate the tank sensor or combination thermostat/ECO assembly clipped to the tank surface.
• Check ECO reset: Some Giant models have a manual reset ECO button on the thermostat. Press firmly until you hear a click. Restore power and see if E3 clears.
• Inspect sensor contact: Ensure the sensor or thermostat is firmly pressed against the tank with insulation properly in place. Poor contact can cause false readings.
• Descale if overheating: If the tank is heavily scaled, elements or burner can overheat the water near the sensor. Drain and flush the tank to remove sediment and scale following Giant’s procedure.
• Replace sensor/ECO: If E3 persists, replace the Giant tank temperature sensor or thermostat/ECO assembly. If you are not comfortable working with 240 V circuits, hire a technician.