Unable to pressure test new gas line?!

So I'm installing a ventless NG heater in my attic. Ran 1/2" black pipe from my basement. About 25-30' of pipe altogether. Pressure tested at 15 psi, no leaks. I cut the 3/4" pipe running to my HW heater and range and tee'd into it. I added the tee, a union, and a 2' length of 1/2" pipe (hadn't hooked it up to the rest of the new pipe yet). I'm now trying to pressure test this part of the system. However, the system won't pressurize at all. The needle doesn't move off the stop of the gauge--I ran my compressor on it for more than 5 minutes. The 3/4" branches off from the meter, and a separate 1" pipe feeds the furnace. The range is off (no separate shut off), and valves to the furnace and HWH are also off. I soaped up the new joints (both when trying to pressurize, and with the gas turned on) and saw no leaks. So where the hell is my air going? All the new joints are right in front of me, and this would have to be a HUGE leak to be outpacing my compressor, right? A few more points:
1. There is SOME pressure in the system--I turn on my stove and can hear air hissing out. Still there after an hour.
2. With the gas on, the meter doesn't budge--it has a 1/2 ccm dial on it which is super sensitive.

All in all, I'm pretty sure I don't have a gas leak under normal conditions. If this was water I'd call it a day at this point. I thought that maybe I had a leak that only showed up under pressure, but again, the system never pressurizes. Maybe there's a bleed down valve at the meter somewhere? So what's my next step here?

I could put a valve upstream of the new joints, but downstream of the main branch point. However, it would involve threading 2 more sections of pipe, and introducing 2 new joints to the system. I bought a NG leak alarm as well...

Any other thoughts?

orionrising said:

one of the new pieces of pipe blocked? Gauge broken?

cap the new end and test at the stove?

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No, if the pipe was blocked that would make the pressure go up quicker. And I can hear the air flowing into the pipes. Pretty sure the gauge works. If I plug the end with my finger the needle moves. Also, the chuck I'm using has a built in gauge that doesn't move. And just for fun I put my bike pump on there... Same thing. How would capping the other end help?

brian89gp said:

You are pressure testing at the 3/4" T you put in on the pipe going to the water heater? Did you shut off your main gas valve at the meter before testing? If I understand the setup right you might be back feeding compressed air through the meter and into the gas comanies lines.

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Gas is off at the meter (I'm wondering though if the valve at the meter has some sort of bleed-off feature?). Anyway, I managed to isolate the branch I'm working on (there was a union at the branch take off that I removed and plugged). Pressurized the system to 15 psi in about 10 seconds. Have found several leaks, none of which were at my joints

One at a union, one leaking valve at the end of an old pipe run that now ends in my daughter's room (took the valve off, capped the pipe), and one coupling in the middle of a long run. I think I'm going to need to cut that section of pipe out and install another union. Oof.

I still have no clue why the system won't pressurize when everything's hooked up...

A1Stoves.com said:

are you relying on the hw heaters valve to hold pressure?
it will not hold much above a lb or so... also, gas cocks wont typically hold 15psi either

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HW heater has a separate shut off--however I'm relying on the range regulator to hold pressure. Not sure if it is. Anyway, plenty of leaks to chase! I wonder how many people have slow leaks and don't realize it? Then again, I wonder if these joints are actually leaking under normal system pressure.

DAKSY said:

You're probably OVER-pressurizing the system.
15 PSI is 30 TIMES the gas pressure in the NG lines
NG is at about 1/2 PSI in your home....
You're probably blowing it the the threads...

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I don't think so. When I isolate the circuit that I just put in it'll hold 15 PSI all day. When I try to pressurize the whole system the gauge doesn't budge, so the system isn't seeing more than 1 PSI max at that point. Basically it acts as if I'm blowing into an open pipe. I took another look at the meter. It looks similar to this. If you look at it, the shutoff is upstream of the meter. In addition, there's a large valve of some sort between the meter and the shutoff. On mine, there's a port labeled "vent". I'm feeling that there must be a blowoff valve somewhere, either for safety reasons or to keep things tamper proof (maybe keep the meter from running backward under pressure?). I found one last union in my system, which is before the main branch point. I'm going to cap it at that point and see what happens.

Again, the system isn't even pressurizing to 1 psi. The valves aren't where it's leaking.

Work's done, my work was done correctly. Just curious as to what on the gas meter is causing the system to bleed all pressure. I never have peace of mind that work has been done correctly, just because a "pro" has been at it. Plenty of hacks out there, in every profession.

Thanks for the helpful info. Reread the posts, check your reading comprehension, and realize why I shouldn't be concerned. As i already stated, my leg of the installation pressure tests fine to about 30x what it sees under normal operation. And if there was a leak as big as it would seem, then a) it would be obvious, and b) my house would have "lifted off its foundation" about 50 years ago. Seriously, you're adding nothing useful to this thread.

Yeah, used black pipe. Next time around might try CSST. After doing tons of copper and seeing how much easier PEX is, I bet it's similar. Except I'd much rather sweat a joint than cut new threads. Actually, there was already pipe running up the wall, capped in the attic. Initial thought was to just use that, but then I realized I didn't know whether it was galvanized/black/other, and I also didn't know whether it was initially used for the radiator heating or gas. That, plus it being probably 100 years old, seemed like a good idea to replace. Not running anywhere close to 2 psi (as I said, my gauge doesn't lift off the peg under normal gas pressures). I need something more sensitive to measure WC--I did put a test fitting just upstream of the heater, so it should be easy to test. Sorry about the bitchy last post...