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error Miller
Error Code P21
Indicates that voltage or current feedback has been detected while the contactor is off, suggesting a malfunction in the internal PID board.
✓ How to Fix It
Consult the Miller Dynasty 200 DX user manual or contact a Miller service technician to diagnose PID board issues.
Source: page 1 of the official manual
From the manual
This error code appears in:
Miller Dynasty 200 Dx Welder