So this 3/4" CPVC fitting was threaded into a Cu fitting in my attic, in the solar hot water loop. It let go with a bang on a nice sunny day with the circulator running and fortuately I was home to turn off the water. The actual domestic hot water is circulated throught the solar panels, it's not a separate loop. As it was there was a lot of water that came out, maybe 20-40 gallons, and fortunately mostly ran out (through light fixtures, bubbled paint, ... Had to replace wet insulation and replaced the fitting with a SharkBite. Question is, how did this occur? Pressure in well pump tank is 45 psi max.