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What actions are recommended if my Ruud Ultra Plug-in Heat Pump with HydroBoost (120V Shared Circuit) displays Alarm Code A104?

CAUTION: For your safety, DO NOT attempt repair of electrical wiring, controls, heating elements, or other safety devices. Refer repairs to qualified service personnel.

Possible Cause: Lower tank temperature sensor malfunction, resulting in the heater being disabled. What To Do:

  1. Thoroughly inspect and ensure the connections of the wiring and sensors are intact and secure.
  2. If you have a multimeter on hand, determine the Ohm reading on the thermistors. It’s important to use the Ohm chart for accurate readings in relation to the current ambient temperature.
  3. On the device’s interface, navigate to Service –> Sensors. A -40°F reading indicates that the circuit is open, while a +250°F reading suggests a shorted circuit. To further confirm this, deactivate the unit, disconnect the thermistor from its board, and re-evaluate the Ohm reading.

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

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