They may add wastewater without realising the unit cannot remove it. Isolation and continued fixture use are incompatible where those fixtures depend on the pump.
What the observation means
A toilet or tap can appear normal while the receiving unit is unavailable. A clear notice and alternative facility reduce accidental inflow.
A useful next step
Keep all known connected fixtures out of use during a fault or agreed service isolation. Do not rely on one person remembering verbally. Restore use only through the appropriate safe process, not simply because the switch has been returned to On.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.