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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.

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  • Looks like that valve broke on the threads... Poor manufacture or cheap valve - the other cause I have seen that looks like that is what happens if they freeze... But I assume that the basement does not get that cold...
    – Solar Mike
    Commented Apr 1, 2019 at 7:38
  • The misalignment of the two valve parts after it broke suggests that the piping may have been under some significant stress. It is possible that thermal cycling, vibration or shock waves in the water may have led to this failure of a cheap valve.
    – Michael Karas ♦
    Commented Apr 1, 2019 at 11:40
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    I mis-aligned the valve parts to show the break detail in one of the pictures. When I first encountered the break, it was not mis-aligned. As my reply to the answer below shows, I did pay close attention to putting stress on the T-junction (and valve). The tank is supported in line with the "T" with very little offset. In my installation area all the input pipes are overhead and it's in the middle of the basement, not near any walls. So I think my installation options are limited to the arrangement I have.
    – PeterT
    Commented Apr 1, 2019 at 13:28

2 Answers 2

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It broke because of the weight of the expansion tank. Only 5 psi on bladder side means it was full of water and very heavy. You need to support your expansion tank. Pre charge should match static pressure. The pressure does not increase or get higher without expansion tank so "overpressure" is not the cause of the problem. Expansion tanks Don't make pressure. They slow its action. Pressure increases slower and decreases slower. A fully filled expansion tank with little pressure on bladder side can like weight 50 pounds.

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  • The expansion tank is supported by straps from the ceiling (not shown, but I should have included a wider shot of the installation, but you can kind of see them white straps in the background of a couple shots). There was no torque on the T-junction at installation time and I couldn't detect any torque when I removed the junction this morning. I'm willing to be wrong about this, but I feel my installation options are limited in my basement configuration and I thought I had it right.
    – PeterT
    Commented Apr 1, 2019 at 13:24
  • I'm going to recharge the tank to 60 psi and see if it holds. If it doesn't, then I'll get a new expansion tank. But I'll be using traditional soldered pipe fittings from here on.
    – PeterT
    Commented Apr 1, 2019 at 13:30
  • Must be faulty valve, pressure could not do that unless pipe was frozen. Ice builds tens of thousands of pounds pressure. But from just water pressure no.
    – plumbum
    Commented Apr 1, 2019 at 13:35
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Almost all valves are made in China or India now and the quality control is terrible. I have experienced more broken castings on valves in the last 3 years than I had in the previous 30 years combined...

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