I have a Hydro-Tek Mega-Tek unit and a non-pressurized horizontal closed loop which was installed in 2006. For the first 10 years we had no problems with this system, but for the last several winters I have a problem where the unit can't keep our house at 70 degrees during winter days when the outside temperatures drop below 20 degrees Fahrenheit. I have had numerous different hvac companies and techs out and they all say the unit is operating as it should, but that the ground loop has become too cold. In early November, the ground loop's temperature was in the low 50's, but now in early-mid January it has dropped into the mid 30's. I don't understand why the ground loop's temperature is dropping. I am not losing any fluid from the ground loop, but the ground loop fluid has never been replaced / flushed to my knowledge either. If a loop isn't loosing fluid what else could go wrong with the loop so that isn't working as well as it for the first 10 years of it's life? Any ideas?