I've finished my PEX supply-side plumbing rough in.

I put a Schrader valve into a push-connect fitting and attached it to one open end and threaded a pressure gauge into another push-connect fitting and attached it to another open end. Then I connected a hot/cold pair of lines to make a closed system, then plugged the rest of the openings with test plugs and put test plugs into all the shower/tub outlets.

I pressurized the system to about 80PSI. Within a few minutes it had dropped to 74PSI, then by the time I was done with dinner it was down to about 50PSI.

I've listened & felt every single joint in the new plumbing - I cannot hear or feel any air escaping. I've sprayed soapy water on all the joints and I don't see any bubbles forming. I've even tested the connections at the valve & pressure gauge to make sure they weren't the source of the leak.

What other methods are there for finding where the plumbing is leaking?

  • There's only air in the system, @JD74, no water yet. Sure, the air coming out of the compressor is reasonably hot, but I wouldn't expect it to loose 30PSI in an hour or so due to cooling. I use the same compressor & hose to fill my tires and don't have that issue. (Unless I pick up a screw or nail in the driveway...)
    – FreeMan
    Commented Jun 29, 2023 at 0:05
  • Do you have shutoffs where you can narrow down where the leak might be occurring? What about filling the system with water and looking for leaks? I've also seen smoke used in automotive diagnosis for AC line leaks, but that required a special machine. Commented Jun 29, 2023 at 0:29
  • PEX expands. It could be if you have a lot of lines they are expanding and the pressure drops. There should be a limit to the expansion. See if it stabilizes and then try adding a bit more air. If the pressure doesn't drop the lines were expanding rather than leaking.
    – RMDman
    Commented Jun 29, 2023 at 0:30
  • There was a glimmer of hope, but it's down to 26 PSI now, @RMDman
    – FreeMan
    Commented Jun 29, 2023 at 0:41
  • 1
    @FreeMan Glad to hear you found the leak :) Commented Jun 30, 2023 at 17:27

2 Answers 2


If you have shutoff valves, you can narrow the parts of the system where the leak might be occurring by shutting off runs of piping and monitoring the pressure.

Also, be sure your drain valves (if you have any) are not leaking and are closed completely.

  • 1
    Silly drain valve... :(
    – FreeMan
    Commented Jun 30, 2023 at 17:27

Soapy water (or the not-so-secret trick of adding some glycerin, or buying bubble-wand solution from the toy aisle) has always worked for me, including on a quite slow leak in my floor-heat PEX loop.

The glycerin (which is commonly in the bubble wand solution) helps with bubble persistence. I think you can also buy bubble-wand solution at 10 times the price as leak detection fluid ;^)

Under the heading of "I don't think you'd ever do this in home plumbing" more exotic leak detection using a helium gas fill and a helium detector is a thing, but it's "an expensive mostly used in laboratories" thing, as far as I know.

  • You sure the bubble-wand solution is more expensive than leak detection fluid? I'd think it would be the other way around. Either way, I'll probably pick something up tomorrow on my way home and give that a shot. Thanks!
    – FreeMan
    Commented Jun 29, 2023 at 0:50
  • If I went the helium route, I'd have the joy of talking funny while I fixed the leak! :)
    – FreeMan
    Commented Jun 29, 2023 at 1:01

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