This is the golden rule of Anden wiring. The unit does not turn on via line voltage. It turns on when a connects the R terminal to the DH terminal.
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This article provides a deep dive into the wiring schematics for the most common Anden models (A70, A90, A130, A210), explains what every terminal means, and offers troubleshooting advice for common electrical faults. This is the golden rule of Anden wiring