So I'm down in the basement last night and hear water running. Turns out I've got water spraying out from a pipe located above the water heater. The water was jetting out from a valve I installed 4 years ago when I installed the thermal expansion tank. There was a significant amount of water and I had to turn off the main water to the house to stop the flow. The clean-up and drying-out is ongoing.
My question for you is about the cause. In the pictures you can see the shark-bite valve and that the failure is along one of the cast lines of the brass case. I'm not sure how this is possible unless the brass casting was defective.... or there are other contributing factors.
Since there is no water charging the thermal expansion tank, I measured the pre-charge pressure and it's only 5 psi. This suggests that the internal bladder has failed (I think), though there is no water coming from the air stem. If the bladder failed, then the plumbing system is logically getting an overpressure. Could this overpressure cause the valve to fail? (I think this is the likely scenario, but I also don't think the valve should have failed at all even with the overpressure. Just sayin.)
How reasonable is it for the thermal expansion tank to fail in just four years? That also seems rather short term. I don't want to be replacing the tank every three years to prevent this.
As an interesting side note, the main pressure reduction valve was replaced (by a plumber) just last year and the overall house pressure was running at about 60 psi.
Any guidance or ideas you might have are definitely appreciated.