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  • What stops a gas water heater thermocouple from shorting out?

    I have a basic propane water heater. Does it matter if the thermocouple wire touches any metal on the water heater chassis? Would this 'short out' the thermocouple?

    I cut an old thermocouple's wire (a thick copper looking wire), and saw that there is no ground connection in it. Looks just like a single thick (~1/16 inch diameter) copper wire between the bi-metal tip and the control box (about 18 inches). I now presume that the ground is thru the chassis of the water heater tank. If all of this is true, it seems reasonable to assume that the thermocouple will short out if the copper wire touches any metal on the tank as it snakes its way between the pilot light and the control box? But I have never seen anything that says not to let the thermocouple wire touch other metal....

    What am I missing?

    thanks

  • #2
    Re: What stops a gas water heater thermocouple from shorting out?

    I think they just get "burnt out".

    I really don't know, it's the most common thing on water heaters, but not as common as a tank leaking. Not enough of a problem to worry about. I don't think I have ever seen a heater go through 2 of em. And I probably see them go bad in 1% of the water heaters I see.

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    • #3
      Re: What stops a gas water heater thermocouple from shorting out?

      a thermocouple is not a wire it is a copper tube so i dont know where you see a wire in it ?
      Charlie

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      • #4
        Re: What stops a gas water heater thermocouple from shorting out?

        The dissimilar metal running down the middle of the tube.

        Originally posted by HVAC HAWK View Post
        a thermocouple is not a wire it is a copper tube so i dont know where you see a wire in it ?
        No, it's not rocket science, it's plumbing and unlike rocket science it requires a license.

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        • #5
          Copper exterior tube is one conductor and wire inside it is the other conductor.

          When heated, the disimilar metal of the thermocouple produces a very low voltage.
          Buthe amperage produced is enough to power an electro-magnet inside the valve enough to hold the safety valve open.
          One of the most clever, elegant, simple inventions of man.
          I'd take an educated guess - but I'm unqualified.
          It ain't just soot, it's paydirt.
          "I swear, wherever Gift goes, argument follows." -Youtube comment

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          • #6
            Re: Copper exterior tube is one conductor and wire inside it is the other conductor.

            If the thermocouple is the type that is a semi-ridgid copper tupe, that outer conducter...the coppper....is connected to ground at both ends buy the connector. Shorting out is a misnomer.
            The inner conductor is isoltaed from the copper by a teflon liner inside. When the dissimilar metal bead on the tip is heated, a tiny current is generated which flows through that inner conductor, through the coil of the gas valve , to chassis ground. That current activates the valve.

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            • #7
              Re: Copper exterior tube is one conductor and wire inside it is the other conductor.

              Originally posted by lovetheUSA View Post
              ... When the dissimilar metal bead on the tip is heated, a tiny current is generated which flows through that inner conductor, through the coil of the gas valve , to chassis ground. That current activates the valve.
              Thelectricurrent from the.rmocouple keeps the safetyalve open, once the metal valve armature is pressed againsthelectro-magnet energized by the current. The magnetism is not strong enough to pull the valve open, but amazingly is enough to keep the valve's metal armature "stuck" to thelectromagnet core once touching it. (Pressing the pilot light button pushes the safetyalve armature against thelectromagnet core.)
              Downstream from the safetyalve is the burner ON, burner OFF valve. The.rmocouple current does not activate that second valve.
              I'd take an educated guess - but I'm unqualified.
              It ain't just soot, it's paydirt.
              "I swear, wherever Gift goes, argument follows." -Youtube comment

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              • #8
                Re: Copper exterior tube is one conductor and wire inside it is the other conductor.

                A thermocoule is not a wire! It is 2 wires...the outer core of which is grounded to the body of the tank by virtue of being threaded into the gas valve. The rest of the magic is both measureable and basic diagnostics. A simple short answer is the outside of a thermocouple cannot short as it is already "shorted" via the thread into the gas valve.
                Last edited by Jones Mechanicals; 10-14-2011, 01:34 AM.

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