Automatic fan control does not work.
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I do not have an Aquastream XT, but let me toss out two thoughts.
Your "Target temperature" (23.0) is very close to your "External temperature sensor" (23.6).
Maybe not enough delta to start it.
Try lowering the target temperature to see if the that starts the fan.
Also, you can select the "Hold minimum power" option, and your fans should always run and not drop below the 35% level you have specified.