Can I replace a gas fireplace valve?

You can replace a gas fireplace valve, if you feel you have the expertise and correct tools. The tools, which include the correct wrenches, hose replacement, valve and valve stem replacement kit, as well as pipe and screw seal, must be obtained first, and then you must turn the gas off at the street (there’s no sense taking any chance). Then, ensuring that all of your tools are grounded properly, as are you, so that no stray sparks can set off any gas which may not have escaped, simply unscrew the fireplace hose flange nut at the wall, and then unscrew it from your fireplace, and attach the new kit.