Error Message E91 may appear for several reasons:

• Insufficient salt concetration in the water → Add salt to the water to the required level as per the instructions in the manual.

• Scaling of the cell electrode → Clean the electrode with vinegar according to the instructions in the manual.

• End of electrode life/wear - This occurs when the hot tub is used intensively or has been in use for a long time, even if the electrodes are clean → The electrode needs to be replaced with a new one.

• The corresponding part number (electrode/titanium plates) can be found in the manual it is a 5-digit numerical code (e.g., 11899). The electrode can be ordered as a spare part.

• Water temperature in the hot tub below 10°C → Check the functionality of the device at a higher water temperature.

• If none of the above steps resolve the issue, it is an electronic problem with the control unit and needs to be repaired by serviceman/ technician.