Aquatherm, no hot water

Is anyone familiar with the Aquatherm heating unit by First Co? The unit, from my understanding of it, sends hot water from the water heater and heats the house using the radiant heat from the water. My problem is that I can't get a consistent flow of hot water unless I turn the heater on and activate the unit. If I don't turn the heater on, I get about 3 minutes worth of hot water, then it turns lukewarm. The water heater is a brand new 50 gallon unit.
Any help is appreciated- thanks in advance! Mark
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