Thermador’s own guidance for E15 and E3100 is direct: turn off the water supply and contact support. This code means a safety switch has detected water in the base of the unit where it shouldn’t be, and continuing to run cycles risks a larger leak rather than resolving the underlying issue.
This is one of the few Thermador error codes we’d call a stop-and-call situation rather than something to keep testing on your own — the safety switch is doing exactly what it’s designed to do, and the right response is shutting off supply, not resetting and trying again.