I have a unit prior to the Firefly so no help there
Has to be that the indicated output doesn’t connect to the Aquahot input
Does your zone 2 pump come on when system heat is selected?
Feel the pex line at the Aquahot and it should be 120 degrees or higher
Zone 2 is used as the stir pump since the 400D units don't have one that is dedicated
That should happen if the system is in the heat mode and the heat exchanger is hot
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