Natural Gas Line Clogged

Hi experts,

Background:
I had a 20-year old gas fireplace that worked fine until several years ago when I started losing pressure (though I didn't know that at the time and thought it was a regulator). Last year, I went ahead and purchased a new burner/log set. In the process of upgrading the fireplace, the installer and I discovered that the end of the gas line was completely blocked with a hard black powder. We broke up the powder, vacuumed it out, and, surprise, everything was working fine.

Fast forward to today:
It's a year later and I'm seeing similar symptoms with the new set. The pilot is fine until I turn the fireplace on, then the pilot lowers and the thermocouple shuts off the fireplace after a few minutes. I assume if I disconnect the fireplace from the pipe in the base of the hearth that I'll see the same black buildup.

My big question - what's this build up and why did the fireplace work for 20 years before it started being a problem. (Granted, I bought the house 8 years ago, so maybe it's always been a problem). I'm just trying to figure out the correct way to fix this

Thanks for any thoughts or pointers !

Ward

Add a trap at the end of the line before the shut off valve.

Consider a new line as this is the pipeline itself likely deteriorating. Old age does interesting things.

Hi Ballvalve,

Thanks for the info and recommendation !

Ward