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I had some gas lines replaced in the crawl space and the next day after the plumber left I noticed a minor gas smell. I got into crawl space with a HomeFlex leak detector and it is clearly going off full blast around one connection. However, I couldn't see any bubbles with liquid leak detector.

I called the plumber back and he also couldn't see a leak with soapy water. I am fairly certain that there is a leak because I smell it and repeated tests with the HomeFlex detector clearly show the area has gas present. It's a bit of a confined space but not completely blocked.

Why would soapy water not show anything?

Is there any additional way to test for leaks? Pressure test?

Resolution

I was able to get some bubbles as a proof of leak. Then plumber tightened the connection and said it's fixed. It was not and my HomeFlex meter was still going off like crazy but I couldn't get anymore bubbles. At this point plumber had more trust in the meter, took apart the joint and discovered badly cut edge on TracPipe and fixed it. After that I demanded full pressure test at the meter which he performed to my satisfaction and there are no more leaks and my meter stays quiet on every joint! I definitely think that this inexpensive meter does a good job.

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    Is this plumber certified/licensed for gas work? In many (most?) areas that is separate/beyond what is required for water/sewer work. If he isn't, get one that is. If he is, and you just can't convince then if he works for a bigger company, get them to send someone else. If he works by himself and you just can't convince him, call the gas company. They'll send someone out, who will find the leak (play dumb, don't show them that you already have a detector), tag it and shut off gas to the house (unless there is a valve for that section). Then call the plumber back.
    – manassehkatz-Moving 2 Codidact
    Commented Feb 28, 2021 at 4:51
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    I've seen the soap thing - and it always seemed hard to do - i.e., hard to see the bubbles. But one advantage of a bigger company is that if you can't get satisfaction you can ask for them to send their best gas person out to take a look. And if they say "you already have the best guy" then tell them you want the boss.
    – manassehkatz-Moving 2 Codidact
    Commented Feb 28, 2021 at 5:32
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    Your statement" for those flex gas lines" does that mean the plumber installed a flexible gas line in that space?
    – Rich
    Commented Feb 28, 2021 at 5:46
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    The gas is coming out from the back of the fitting on CSST. He just didn't do it right. And this connector is coming straight up so soapy water drips off it immediately. I managed to get some bubbles of it eventually and made a video.
    – Uncle Meat
    Commented Mar 1, 2021 at 7:10
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    If you have to convince your plumber that you have a gas leak, then I would recommend that they not be your plumber any longer. Vacate the building and have a qualified inspector come out right away. If the plumber refuses to fix his work, file a complaint against their license and have someone else fix it. Then hire an attorney who is more competent than your ex-plumber. Also write reviews to warn others. Gas leaks are no joke.
    – End Antisemitic Hate
    Commented Mar 1, 2021 at 23:55

6 Answers 6

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The other answers here are good from a technical point of view about how to verify a leak, but to answer the question of "how to convince a plumber", I'll second a comment by @manassehkatz: call the gas company.

Any time I've suspected a leak the gas/energy provider has been very quick to send someone out with their own tester (not just a soapy water check). They are quite literally professionals at detecting gas leaks.

If they find evidence of a gas leak, that should be reason enough for the plumber to re-check and redo the work.

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    The gas utility is the only way to go . They found a leak in my stove after I had bubble tested al ACCESSABLE connections.
    – blacksmith37
    Commented Feb 28, 2021 at 23:08
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    @Rich It's better to send a young person with a keen nose instead of an old fart that doesn't believe you who has been desensitized to mercaptan. At least the young person would be able to get someone more experienced to take a look.
    – MonkeyZeus
    Commented Mar 1, 2021 at 13:12
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    So of course from a safety perspective turning the gas off is obvious. I know I can turn my gas off at the meter myself though so I wouldn't call the gas company just to turn it off. However, once the gas is off then how does someone find the leak subsequent to that? I'm not suggesting OP not have their gas turned off but it seems like a chicken and egg problem and I'm curious how one resolves the leak once the gas is turned off.
    – Dean MacGregor
    Commented Mar 1, 2021 at 18:30
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    @DeanMacGregor Unless the leak is really obvious and large, then they turn the gas back on, use the electronic tester and remember to ventilate the area before and afterwards (and then shut it off again and wait for repairs).
    – mishan
    Commented Mar 2, 2021 at 8:28
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    And if the gas company finds a leak and tags your meter out, the plumber will be responding to unarguable issue with a clear resolution.
    – Nathan Goings
    Commented Mar 2, 2021 at 19:06
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You have to use a lot of liquid detector and large leaks can blow right through without making bubbles; however, typically a leak this large would be easily detected by the Mark-I human sensors you were born with. The general rule is- big leak=big bubbles, small leak=small bubbles, tiny leak=tiny bubbles.

Remember that the odorant (mercaptan) will remain in old pipes and create a strong smell, so look around for discarded pipe and/or fittings that are in the space and remove them, to help narrow down your search.

Typically, the AHJ (Authority Having Jurisdiction) will require a pressure leak-down test for any significant addition and/or alteration to gas supply lines. If you did not pull a permit for the work, the AHJ doesn't know about it (obviously) and it is your decision whether or not to involve that agency. Work with the contractor and keep telling them you suspect a leak...

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    I'm going to have to remember "Mark-I human sensors" for later use. Good stuff! My only addition is that in my area- a large US city- during a pressure test corrugated gas flexes can only be used at specific appliances - not water heaters - and are disconnected and not tested. Only building piping is subject to a pressure test.
    – Rich
    Commented Feb 28, 2021 at 21:34
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Try to fan the area with fresh air to the point the detector detects nothing then immediately use the detector to zero in on the area where the gas begins to appear.

Try using saran wrap to isolate the detector around each joint.

Try a bottle of leak detector fluid. Sure it's overpriced soap but in this case the $5 may be worth while. Try being generous with it.

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    !!! try NOT to use electric equipment (e.g. fan) in a place where you smell gas or otherwise suspect gas presence.
    – fraxinus
    Commented Feb 28, 2021 at 22:06
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    I was able to get some bubbles with Oatey leak detector after dozen of tries. Very uncomfortable spot to do it. I first noticed that some quick small bubbles get immediately blown off. But eventually it picked up enough soap to blow actual bubble.
    – Uncle Meat
    Commented Mar 1, 2021 at 7:03
  • @fraxinus isn't it okay to use one in a well ventilated area, to blow fresh air towards where you think the gas is?
    – user20574
    Commented Mar 1, 2021 at 11:12
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    @user253751 it is only somewhat safer - unless you make sure the mixed air doesn't return back - e.g. with air ducts. There are explosion-safe fans, too, but the average homeowner usually doesn't have one available.
    – fraxinus
    Commented Mar 1, 2021 at 12:42
  • @user253751 only if you are absolutely certain there will not be a spark. There are special fans certified for those situations, but you probably don't have one of those. Someone at my department put a small sample with flammable material in a normal fridge. When the fan started, luckily in the middle of the night, the door of the fridge ended up on the other side of the fairly large room.
    – Davidmh
    Commented Mar 3, 2021 at 16:11
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You haven't mentioned whether this is natural gas or propane. If natural gas, then use the analog dials (or digital read-out) on your gas meter. Hopefully your meter will have a dial or indication for a small unit like 1/2 cubic foot.

Attempt the following only if you're familiar with procedures for re-lighting any pilot lights your appliances may have. Shut off all consumers of gas: water heater, furnace, fireplace, stove, clothes dryer, barbequeue, and any other gas appliances. Turn off pilot lights too. Make a note or take a photo of the position of the dials on the meter.

After an hour (or longer if you're not anxious to get the gas turned back on) go out and compare the current readings against the recorded reading. Has it changed? If the meter shows gas was consumed it had to have gone somewhere.

For reference: a small gas burner on a range might consume 400 Btu/hr. At typical density of 900 Btu per cubic foot, that burner would consume a little less than half a cubic foot in an hour -- the 1/2 cu ft dial would turn about one full revolution. The dial might have 10 divisions; movement by one division represents about 45 Btu. A much smaller deviation would still be noticeable though: 1/5th to 1/10th of a division is probably perceptible and represents 5-10 Btu.

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    Good idea about watching the meter. I suspect, though that the leak is really small so it may take a lot longer than an hour to get dials move. I will have to see if we can go without heat and hot water for that long.
    – Uncle Meat
    Commented Feb 28, 2021 at 6:22
  • If the leak is that small, then it is not a danger. At this point I would begin to wonder if the consumer grade leak detector was falsely signaling a leak was present.
    – Jim Stewart
    Commented Feb 28, 2021 at 13:01
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    Tried meter and it did show some gas flow. Approximately 1/4 cf over an hour. The I gave it another try with Oatey leak detector and finally was able to get some bubbles after dozen of tries.
    – Uncle Meat
    Commented Mar 1, 2021 at 7:00
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    @JimStewart - even a tiny leak will allow gas to build up over time, in a non-vented area. Apply spark - bang. That's not a danger?
    – Tim
    Commented Mar 2, 2021 at 9:30
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    Every area is vented enough to keep the level of gas below the dangerous level for true micro-leaks. But I do not advocate tolerating significant leaks. Call the gas supply company and have them do a PROPER pressure test. Latest info from OP indicates the system will fail.
    – Jim Stewart
    Commented Mar 2, 2021 at 12:11
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First convince yourself.

Soapy water can be tricky - you may not see small bubbles in hard to observe places. The right amount of soap in the water is tricky as well.

Try to hear the leak.

You may need to ask people in the house to go out and/or stay quiet for a while and/or turn off noisy equipment (heating, washing machine, etc).

You may also need few minutes to adapt to the silence and slowly move your head left and right around the suspected place.

If you can hear it, the exact leaky spot can be determined by touching - a finger over the leak changes the sound.

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You will only be able to do this if you have a shut off valve and a suitable point to attach a manometer

shut off all gas appliances

shut off the gas supply

connect a manometer to the gas line

turn the gas back on - this will pressurise the line, take a reading

take a reading 10 mins later, if the reading is less, you have a leak

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