What happened?
On the CORE One/+ equipped with the INDX system, the vertical Z offset is measured during the Tool Offset Calibration. If the measured Z offset deviates beyond the safe allowed limit, the printer will show the following message: "The measured Z offset exceeds the safe limit. Make sure the nozzle and the sensor are clean. Caution: the nozzle may be hot."
Error name: Unsafe Z Tool Offset
Error code: #36131 (CORE One INDX)
How to fix it?
Make sure that the filament is fully unloaded from all tools before starting the calibration process.
Nozzle cleaning
Use a small brass brush to clear away any old plastic stuck on the nozzle. Avoid contact of the brush with the hotend cables, as this could cause a short circuit.
Tool offset calibration
Go to the printer menu in Control -> Calibrations & Tests -> 12. Tool offsets calibration and redo the calibration.
Reduce vibrations
Any vibration propagated to the surface under the printer, or an unstable surface under the printer, might cause a false reading on the load cell, triggering the homing error.
For example, a printer that is in operation next to your printer can cause vibrations that are propagated to it, potentially causing a tool offset calibration failure. In that case, stop any printers next to the CORE One with INDX, and reattempt the calibration.
A possible solution to dampen the noise and vibration of a printer is to add some additional padding underneath the printer.