Most folks here know this already, but I figured it's worth a short post for some.
I recently noticed a soot buildup on the fiberglass above the water heater. This is almost surely the result of a clogged gas tube causing inefficient burning of the propane
. It doesn't take much of a restriction to cause that, and it's often just a spider web as it was in this case. It's easy to remove the tube and run something through it to remove the restriction. If this has not happened to you yet, chances are it will at some point and you can quickly correct it without a time consuming, costly visit to the shop.
All I had readily available to ream out the curved tube was a large cable tie, but that was enough to bring me back to a nice, blue, clean flame.