Stiebel Eltron heater shows E15 and shuts down; may be associated with ground fault or insulation issues.

Safety: This is a potential shock hazard. Turn off power immediately and do not operate the unit until the fault is resolved.

• Visual inspection: With power off, remove the cover and inspect for burnt wiring, melted insulation, or signs of arcing to the metal chassis.
• Check for moisture: Look for water or condensation near electrical components. Dry thoroughly and address any leaks as described for E12.
• Test elements to ground (advanced): Disconnect heating elements and measure resistance between each element terminal and ground. Any low resistance indicates a ground fault and the element must be replaced.
• Professional service: Because ground faults involve safety-critical components, have a qualified technician replace faulty elements or wiring and verify proper grounding and insulation resistance before returning the unit to service.