What steps should I consider if my Ruud Ultra Plug-in Heat Pump with HydroBoost (120V Shared Circuit) shows Alarm Code A900?

CAUTION: For your safety, always handle electrical components with care to prevent potential hazards.

Possible Cause: There seems to be a controller malfunction, leading to the heater being disabled. What To Do: Replace the Control Board.

This answer is applicable for the following model: Ruud Ultra Plug-in Heat Pump with HydroBoost (120V Shared Circuit).