I've got a salamander (or torpedo) style propane heater with apparently a bad thermocouple, it lights but won't stay lit after releasing the by-passbutton. How does this style of thermocouple generate a voltage without 2 wires. Since the t/c was bad anyway I cut open the copper tube finding only a single un-insulated solid, what looks to be copper, wire. There can't be a potential difference between the copper tube and wire as neither one is insulated and the clearance is minimal between the 2 pieces so at any bend they touch. Guessing it still current flow because the device it attaches to in the safety valve on the by-pass button appears to have a coil winding similar to a solenoid. I'm familiar with 2-wire thermocouples, i.e. chromel/alumel, iron/constantine etc. rtd's and thermistors but I don't have a clue how this one works and they are on most standing pilot valves.