Error Message E91 may appear for several reasons:
- Insufficient salt concentration 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 a serviceman/technician.