Compression fitting wobbles and slides on undersized copper pipe
Some copper pipes have a smaller outer diameter than standard fitting interiors, which causes compression and press-fit connections to wobble instead of gripping tightly. This mismatch prevents the fitting from forming a proper seal, resulting in persistent leaks and assemblies that easily rotate or slide right off the pipe.
What the numbers show
Counted from the threads quoted below. How we count
- People have been saying this in most months since September 2026.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1Removing the press fitting and soldering a new stub out with an MIP and threaded ball valveDid this help you?
- 2Wrapping the fitting with a rag and repressing in the same positionDid this help you?
- 3Sweating or soldering a valve or male fitting onto the copper pipe insteadDid this help you?
- 4Calling a professional plumberDid this help you?
- 5Sweat the joint to fill the gap with solderDid this help you?
- 6Use a female threaded adapter instead of a sweat fittingDid this help you?
- 7Remove the valve cartridge before heatingDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“However, this copper had a smaller OD than any pro press or solder fitting ID than usual, causing it to wobble and not seal.”source ↗
“I actually tried that twice. It didn’t make a difference.”source ↗
“After replacing the valve, I cannot for the life of me get the compression fitting to work.”source ↗
“No matter what I do, the entire assembly still fairly easily rotates and slides on the copper pipe!”source ↗
“I can get it to a magic location where there's only a tiny slow weeping leak but move it a bit and the pipe slides out more and it's spraying again.”source ↗
Where this came up
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