[rickst29]

By looking at an electrical wiring diagram, I didn't see that the propane supply tubing goes right through the Thermostat.

So the sequence of controls is this:

#1: Propane control circuits must activated (electrically) at the selector switch).

#2: Propane supply line goes into the thermostat, where it is valve- controlled. I don't know if it is a "fully open OR fully shut" type of valve, or whether there really is some finicky control done there. (I think that it's only On/Off, because the attached diagnostic procedure doesn't test for "if open, how much".)

#3: Propane line out of the Thermostat, where it becomes thermocouple controlled.

I've attached the propane "won't stay lit" diagnostics page, leaving out the various thermocouple voltage settings and their regulation of the valve (stuff at the bottom).