Atlantic water heater displays E21; unit may not heat or may behave erratically.

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Corrupted EEPROM on control board, power surge, incorrect board version installed, failed firmware

Safety: Switch off power before manipulating electronics.

Turn power off for at least 2 minutes, then restore power to attempt a soft reset.
If your Atlantic model allows, perform a factory reset from the user menu (consult the user manual).
Verify that the installed control board part number matches the heater model.
If E21 persists, the control board memory is likely corrupted. Replace the Atlantic control board with a new, pre-programmed unit.

Hard 4/5

Electronic Control Board

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