When we bought our house 6 years ago it came with a propane gas log fireplace inset in a fireplace that was converted from a wood burning fireplace. It worked great up until yesterday after we had our tank pressure tested and filled. It now makes a strange sound like there is air in the lines. If you turn the flame off manually and turn it back on it stops. It is also not turning on as frequent as it was before.

Can you better describe the sound "strange sound like there is air " unignited gas will make a hiss. Does it have a pilot light and a control knob?

It has a pilot light that is a pretty blue color and a contol knob. When it comes on most of the time it lights correctly but every now and then it lights hard. The sound it makes sounds almost like it is in a tunnel a deep roaring noise.

I am not an expert, but I have this same issue and this is what I found out for my situation. Use the info at your own risk.

It's probably a safety release device inside the tank that trips the main burners when the chamber gets too hot. You will still be able to light the pilot (and it will stay lit for about 3 minutes) but if you try to turn on the burners via the thermostat, it makes a roaring noise and the pilot is blown out and no propane is allowed to flow through the burners.

This is what I've found out.

The overheating problem is likely environmental:

Poor venting - clogged vents sides and bottom. My hot water heater requires 1" vertical for every 1/4" horizontal - not sure what this means (just got this info 5 minutes ago) but sounds like it's a ratio I must use to ensure proper ventilation

Low gas pressure - haven't figured out how yet, but check gas pressure

Flammable vapors in the area - cat litter, cleaners, etc.

Oxygen flow - fire need oxygen, biatch.

So in my case, I needed a part called a TRD, thermal release device, and you can't buy it, GE has to send it to me and a licensed professional "must" install it.

That's my story, hope it helps someone. And as a sidenote, taking the burner out of the hot water heater is a piece of cake. Just follow instructions, make sure you have the right size tools, LOOK at the parts and THINK about what you're doing and be prepared to use a little force to take the burner out -- the gasket will have melted a bit to the chamber frame. Also, call the warranty number for your hot water heater EVEN IF THE WARRANTY IS EXPIRED. You'll be surprised how helpful they'll be despite having no coverage.