I've checked the thermocouple and it was tight. It's not a left hand thread by the way. Is the tightening necessary to get electrical contact? What I don't get is this happens 2 years in a row and I remember now that only the thermopile was replaced 2nd time. It seems that the gas valve is not the problem. How do thermopile and thermocouple differ in operation?
OK, that helps. I'm assuming then the thermocouple generates millivolts but I don't understand how because there are no wires like the t-pile has only a copper line from it to the valve. Also, if the valve itself is bad is it repairable or junk?