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Thread: Thermocouple

  1. #1
    Join Date
    Jun 2005
    Posts
    1

    Question

    Just tested the thermocouple on a
    Robert Shaw 7000 series gas valve.
    As described here, we got 27--30 mV
    from the thermocouple tip when
    heated with the pilot flame but when
    screwed to the gas valve, the
    thermocouple tip presses onto the
    end of two heavy gauge wires that
    seem to go up to some other point
    in the wall furnace.
    What is the purpose of those two wires?
    Without them the pilot stayed lit
    and gas valve seemed to
    function correctly.
    It seems difficult to understand a
    circuit when the tips of the two wires are
    pressed together by the end of the
    thermocouple.
    Is this a safety feature or a
    necessary part of the operation?
    Thanks


  2. #2
    Join Date
    Feb 2004
    Location
    Maine
    Posts
    483
    Oh my god

  3. #3
    Join Date
    Jun 2003
    Location
    Florida
    Posts
    9,548
    I highly recommend you step away from the furnace and have a pro look at it. Two people just lost there lives here in Fl. from co poisoning.....don't play with fire.
    If everything was always done "by the book"....the book would never change.

  4. #4
    Join Date
    Feb 2004
    Posts
    2,474
    SAFETY--Yes Do not eliminate.

  5. #5
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,121
    Man, were are you were your concerned about heat this time of year it's 100 in Houston in the shade please invite me up I will fix it for free.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  6. #6
    Join Date
    Feb 2004
    Posts
    2,597
    you need a new gas valve.

    shut off the gas supply immediatly to prevent danger to you and your family.


  7. #7
    Join Date
    Nov 2001
    Location
    Moose Jaw, Saskatchewan, Canada Occupation:Interprovincial Plumber, Commercial Gasfitter Interests:
    Posts
    2,414
    That's not a gas valve problem, it's a safety problem. You need somebody who knows what they are doing to look at it.
    I love my job, but paydays Thursday

  8. #8
    Join Date
    Dec 2003
    Location
    Location!, Location!
    Posts
    929
    "Is this a safety feature or a
    necessary part of the operation? "

    wtf?

    read that part again?
    is this YOUR home?

    Yes-the name is TCO- It is a safety device which interrupts the pilot circuit with a thermal cutout.


    leave it 4 a pro-don't be a doofus.
    If you knew what was going on, you wouldn't say:
    "It seems difficult to understand a
    circuit when the tips of the two wires are
    pressed together by the end of the
    thermocouple."

  9. #9
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,770
    Call a pro.

    Need to find out why it tripped.

    Don't bypass it.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  10. #10
    Originally posted by billva
    you need a new gas valve.
    Really, I see a faulty limit due to improper flu piping/termination!

  11. #11
    i think he's implying that there was in incorrect installation in the first place causing the thermocouple connection to short out. It could have functioned that way for a long time before the heat or pressure or something caused the insulation on those wires to fail shorting the thermocouple causing the valve to shut off in safety.

    I'd say that you need to call someone to come out and fix the thing If you think it was installed in a way that crimps the wires from the thermocouple then call someone ELSE rather than the guy who installed it in the first place

    Hard to get any specifics as to why it's unsafe with all the people scared to death that you're futzing with it, but without the thermocouple it can't tell if the pilot light has gone out and will flood your house with gas and it will blow up and kill you.

    That would be bad, so do not defeat those connections and do not just leave it. Get it fixed asap. If it's going to take more than a few hours to get someone out there the advise to turn it off in the meantime is very good.

  12. #12
    Originally posted by jfs1138
    i think he's implying that there was in incorrect installation in the first place causing the thermocouple connection to short out.
    No, I believe he has a problem and doesn't know how this system operated from the OEM.

    It could have functioned that way for a long time before the heat or pressure or something caused the insulation on those wires to fail shorting the thermocouple causing the valve to shut off in safety.
    Shorting the wires together is not going to cause this unit to fail the pilot valve!

    Shorting then to the cabinet is a totally different animal.

    Hard to get any specifics as to why it's unsafe with all the people scared to death that you're futzing with it

    That's because WE are familiar with this set-up and the safety limit is most likely on the flu hood!

    but without the thermocouple it can't tell if the pilot light has gone out and will flood your house with gas and it will blow up and kill you.

    If he doesn't understand this simple idea... He has NO BUSINESS messing with it further!

    That would be bad, so do not defeat those connections and do not just leave it. Get it fixed asap. If it's going to take more than a few hours to get someone out there the advise to turn it off in the meantime is very good.
    Further, if the wires are connected (together) under the valve (beings the coupler was tightened to tight), this would not cause the pilot to go out!

    This may sound HARSH, but this can be a very serious issue!

  13. #13
    This may sound HARSH, but this can be a very serious issue!
    No, you're right of course. perhaps it's just me, but when I ask a question I'd like more information than just yelling at me that i have no business asking the question.

    Why wouldn't shorting the wires together cause the pilot to go out? That would stop the micro current from the thermocouple from getting to the sensor and it would think the pilot had gone out wouldn't it?

    I can't really tell from his post if he's talking about the wires from the thermocouple or some other wires inside there. And I don't really think it matters. It's installed incorrectly or just busted if it doesn't work when tightened into position.

    I think the classy thing to do would be to give him enough information so that he understands that he aught to call someone rather than just telling him he has no business touching it. If it were me that would make me angry and I'd want to try all the harder to do it myself. Whereas when I understand enough to know I'm out of my depth I'd be thinking, what a nice group of guys there on the internet to be concerned enough about me to explain why i needed some help on this project.

    If he's the type of guy that will take that little bit of info that would show a normal person that they need help and try to do it anyway, then no amount of telling him to call someone else is going to work anyway. So you might as well give him the benefit of the doubt.

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