Atlantic digital water heater displays E3 and does not heat; sometimes occurs after overheating event.

Safety: Isolate electrical power and allow the heater to cool completely (at least 30–60 minutes) before attempting reset.

• Remove the access cover to reach the high-limit safety thermostat (often a red button on Atlantic electric models).
• Press the red reset button firmly until you feel a click. If it immediately trips again, do not keep resetting; investigate the cause.
• Inspect the heating element area for heavy limescale buildup. Excess scale can cause hot spots and trip the safety. If necessary, drain the tank and remove the Atlantic immersion heating element for descaling or replacement.
• Check that the control board relay is not welded closed (element should not be energized when thermostat is open). If the relay is stuck, replace the control board.
• Verify that the thermostat is firmly attached to the tank surface or well; poor contact can cause false overheat readings.
• After correcting the cause, reset the thermostat again, restore power, and monitor a full heating cycle to ensure E3 does not reappear.