I just had several sections of Nibco PEX break and flood our garage and damage the drywall. I decided to get into the attic and photo the writing on our PEX lines before the house was destroyed due to raining inside. Appearantly the primary plubing contractor installed a superior in-floor variety called RAUPEX. Thankfully this stuff is cross-linked and even if it splits it won't leak. It's a PEX"A" type quality. If you don't know what you have you'd better investigate. If you see Nibco then you better cut way back on your water heater temperature and get prepared for the worst. Hopefully you can replace it all before it breaks.