I have a 15 year old payne furnace. About once every couple of days it will heat the house up to the thermostat temp, shut down, and when the temp drops back below the thermostat, it will fail. The flashing code indicated that it tried to fire the gas but failed 3 times. Since it was so intermittent, I really wasn't able to troubleshoot anything. I ended up removing the flame sensor which looked brand new, but I wiped it clean anyway. Then I checked the resistance of the ignitor and it was within specs. So I waited for it to get worse, and it finally did yesterday. I was able to stand there while it failed and see that the igtnitor would glow orange, there would be some clicking sounds, but the gas didn't ignite. While it was attempting the second try I wiggled the wires at the gas valve assembly and it fired up the gas for about a second or two and then stopped. I thought it might be a loose wire, so I powered down and removed the wires, but they were not loose or dirty. When I put it back together it wouldn't work. I ASSumed it is not getting gas to the ignitor so I wanted to try and figure out if the valve assembly is bad or if the circuit board that sends the signals to the valve assembly is bad. Does anyone know a troubleshooting technique to isolate the problem? I don't have any fancy testers, just a standard volt/ohm/amp meter.