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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.

Uncle Meat
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6 Answers6

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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.

TylerW
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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...

Jimmy Fix-it
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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.

jay613
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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.

Greg Hill
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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.

fraxinus
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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

Roger
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