We use a regency Gr55-3 ~20,000btu gas fireplace for heating our bedroom. Its about 10 years old and has given us no trouble before.

The gas supply line is a small (3/8"?) flexible copper tube that runs about 40' from a prv. I believe the prv lets pressure down from 2psi to a few inches of water.

This year when I first turned it on for heating season, everything appeared to work although the gas valve in the fireplace took a few tries with the thermostat before it finally opened. About a day later, the pilot light was running at about half its normal flame height, and the main burner would not come on. Now there is no gas coming out the pilot light when I try to light it.

Is this a prv problem (i.e. no gas) or a gas valve problem at the fireplace? Any sensible way to troubleshoot?

I would start here first at the prv.

Thanks. Turns out the PRV was fine... I forgot we supply the BBQ off the same PRV, and the BBQ has lots of gas.

I cleaned up the gas supply valve and the rest of the fireplace and things seem to be working again. Plus I re-aimed the pilot light a bit so the flame was directly on the thermo-thing. I think there was not enough heat on the thermo-thing to keep the pilot light going.

The pilot light went out again... but now I'm sure I fixed it.

Initially I thought it was the thermopile (the electronic gizmo that turns the pilot gas off if the pilot light goes out.). However my local fireplace store was nice enough to give me some information. If a multimeter reads 325mV or greater across the terminals when the pilot light is lit, then the thermopile is fine. Mine was reading >400mV, so that was not the problem.

So next stop was the pilot gas line. The pilot gas tube runs from the gas valve to the pilot light burner. At the bottom of the pilot burner is a small orifice about the size of a pin. You need to remove the pilot gas supply line to get at it. It turns out this was mostly plugged. A quick shot of compressed air and its completely free.

The pilot light flame is now about twice as high as it used to be and all is right with the world again.

A plugged orifice will also give the impression of a out of gas situation. Glad you got it going.