“dE” on a Thermador induction or electric cooktop means demo mode is active — a genuine, documented display state originally meant for in-store demonstration units, not a malfunction. If a unit was ever powered on without properly exiting this mode (or if it was reset for any reason), the cooktop will refuse to heat any zone while dE is showing.
To exit it: disconnect power to the cooktop at the breaker for about 30 seconds, then restore power and touch any control within roughly 3 minutes of it coming back on. If dE reappears immediately after that sequence, that’s the point where it’s worth a technician visit rather than repeating the reset.