Propane wall furnace not firing
Try adding a jumper wire to the gas valve to see if that will fire the wall furnace. If it does, the problem is in one of the devices in control system.  Jumper out each device until you find the one that has failed. Take down the control's model number and see if it one that is recommended for a thermopile system. All devices used with a thermopile system are made special for that type system. The thermostat used with a thermopile system is not a standard type thermostat; they usually do not use mercury.  All the devices have special contacts that have very little resistence since the thermopile has a voltage output of about 3/4 volts. Next, when you jumper the thermostat wires at the gas valve and the unit will not fire, you should have a service tech check to see if the gas valve is opening and allowing gas flow but the flow is not getting to the burners. If this is the case they may need to remove the burner or burners to see if a spider or bug has made a home in the orfice of the burners.