how much water should be added, to a non pressurized system? im adding water to mine daily. is this right? does it steam off that much? im at a loss here. i use pex al pex on my supply and return line as well as my fill line. (pex, aluminum jacket, pex, hence "pex al pex". water temp is set at 160, but ranges from 160-190. is the water expanding out and steaming that much?