A couple months ago, I posted about a furnace that had suffered neglect. So what else is new? Today, I got to go back to the house, but not to fix the furnace. The consulting company that went to do an energy audit goes and frequently finds, gas leaks in the lines. This actually more common than you may think; even in newer homes. The reason for this vary, but poor installation is the most frequent. I've installed gas lines for the past 20 years and the only reason they leak is because they aren't sealed and tightened properly. This means using a decent amount of sealant (not plumber's tape), and threading the pipes together tightly. In theory, fixing these leaks if pretty simple, but what if you have a leak on the main line, in the middle, and the only way to tighten it is to undo every pipe on the furnace, water heater, fireplace,etc. Even with the respective unions, this is going to be an all day job and believe me I've been there.
However, there are alternatives and with a little forethought, a union, a few pipe nipples, a fitting or two and some pipe sealant, you can make short work of nearly any leak you come across. You will also need a good drop light, ladder, a couple of pipe wrenches (for 3/4 or 1 inch gas pipe) a reciprocating saw with a metal cutting blade, and some bubble solution to check for leaks. You can substitute larger gripping or groove joint pliers instead of wrenches, but they're really not that expensive and still the best tools for the job. Again, when in doubt call a home service professional to perform the repairs. Paying him or her will be less expensive than an insurance claim, or a trip to the emergency department. Since I'm not on the job with you, I have no control over the quality of your work. Do this an all other repairs at your own risk.
First, shut off the gas at the meter and run the furnace. Then shut the electricity to it and any other fuel burning appliance off. To get to the leaking fitting, you need to find a joint you can cut with the saw. This can be a fitting or pipe nipple, but the idea is to cut a piece of the pipe or fitting without getting out a threader. This is because threaders are time consuming, dirty and cumbersome for just fixing one or two joints. We want to save time, not add more to the job or break out more tools. I prefer cutting a 45 or 90 elbow over a straight coupling because the saw is less likely to mess up threads. Whatever you cut, remove it, take apart and reseal the leaking fitting and use the union to join the pipes together in place of a coupling or in between two elbows with pipe nipples. This is much better than taking the whole works apart and then trying to get it back together. Turn on the gas and use the soap bubbles to check for leaks. If you're satisfied there are none, turn on the appliances and make sure the burners in each come on. Maranatha!