A tech came out to look at our basement concrete floor radiant heat and said the delta T was too great returning from the floor loop. He thought the unit may be having a hard time keeping up. As a result he increased the temp from 120 deg to 130 deg on the tank. He decrease the pump speed for the floor and increase the pump speed between our GSHP and the tank. Does that make sense? It seems to me that if the delta T was too great that you would want a higher pump speed to the floor.