Very old forced air gas furnace keeps running.

Discussion in 'HVAC' started by auntybb, Nov 7, 2011.

  1. Nov 7, 2011 #1

    auntybb

    auntybb

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    My friend has an old house with an old gas furnace. After she had her thermostat replaced she continued to hear her furnace running after it kicked on. She has no money, and like me, is a woman of a certain age. She's afraid to call a repairman because she's afraid that he'll tell her to get a new furnace. Is it possible that my friend and I could fix this with instructions? We are NOT skilled. She is more hopeless than I am. Her husband has dementia and is always cold. Thank you.
     
  2. Nov 8, 2011 #2

    paul52446m

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    You have to be more detailed, Are you saying the heat keeps going so its over heating? or are you saying the blower won't turn off? Can you take pic. of the controls with the covers off. so i can see what you have. Paul
    paulm989@hotmail.com
     
  3. Nov 8, 2011 #3

    joecaption

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    The key is, the thermostat was changed and then it stated messing up. Who changed it?
    One wire put in the wrong place or the wrong thermostat and it's not going to work.
     
  4. Nov 8, 2011 #4

    auntybb

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    Thanks, Guys,
    Sorry that I wasn't clearer. The heat continues to blow after the furnace kicks on. She had her thermostat changed by her bro-in-law because he thought that a new one might solve the problem. Unfortunately, the furnace continues to blow heat until she turns off the electricity to the old monster.
    I have never been in her basement, but I'll be happy to take a picture for you later this week.
    I truly appreciate the help. She's in a tough spot.
     
  5. Nov 8, 2011 #5

    paul52446m

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    First we have to find out if the problem is in the stat , wiring, or furnace. When the heat keeps going you need to go to the furnace and take one stat wire off and see if the burner goes out. If it doesn't then the problem is in the furnace.
    Could be a sticking gas valve. If you check it by taking a stat wire off at the furnace, let me know what happens.
    When the stat is turned down for a hr. or so, when you turn power on does it
    fire up with out turning up stat? Paul
     
  6. Nov 11, 2011 #6

    auntybb

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    Thanks, Paul. I'll do it. Where is the stat wire going to connect on the furnace? I'm willing, but you'll have to go slowly with me. Actually, I'd love to learn something about this. I'll check it this weekend.
     
  7. Nov 11, 2011 #7

    paul52446m

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    I would suggest you take the doors off the furnace and take some pic. because its hard to answer question when i can't see what we are working with.
    paulm989@hotmail,com Paul
     
  8. Nov 15, 2011 #8

    auntybb

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    Hi, Paul,

    I have several photographs, finally. I wasn't sure what you might want, so I took a bunch. How should I send them to you? Upload? Email? Thank you so much.
     
  9. Nov 15, 2011 #9

    paul52446m

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    just email them to me. paul
     
  10. Nov 16, 2011 #10

    auntybb

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    Hi Paul, My camera wouldn't take really-close closeups, so this is the best that I can do. I tried to get all of the angles, but I had no idea what I was looking for. I have one more photo, but the message would only let me send five. I'm curious to know if you can even see what's there. Thanks again. Kathy

    HPIM3755.jpg

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  11. Nov 17, 2011 #11

    paul52446m

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    Ok first lets id the parts, Pic. 2 is your gas valve. Pic. 3 right top is your fan and limit switch.
    In pic. 5 there is a small wire entering the furnace. This wire looks like it's tight against the metal on the top side of the hole. Check that out to make sure you don't have a bare wire touching the metal furnace.
    Leave the door off the furnace so you can see the burners. Now when you turn the stat down and its still going, take and tap the side of the gas valve, this could let us know if we have a sticky gas valve.
    If it still on then in pic. 2 you have 3 wires on the front of the gas valve,
    take a pair of pointed pliers and take the left hand wire off and see if it turns off. if it does then the problem is in the stat or wires going to the stat.
    This unit looks pretty rusty, stand in front of the furnace and have someone
    turn the furnace on. Get down so you can watch the flame on the burners.
    When the blower comes on is there any flame floating around. If there is you need to have the heat ex-changer check because you could be getting
    carbon monoxide.
    Are there any other bare wires in the furnace?
    There is a wire going from on top the gas valve over in front of the fan switch and it keeps going to the right, where does this wire go?
    Start checking out these things and get back with me. Paul
     
  12. Dec 5, 2011 #12

    auntybb

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    Hi, Paul, Getting back to you has been delayed by a case of the flu and a death in the family. So life goes.
    I followed all of the steps that you gave me, and nothing changed. The furnace seems to burn clean and to snap right on. Removing the wire didn't turn anything off. Nothing is touching the furnace. I guess that some sort of switch or timer must be bad. But you're the expert. Please give me more directions, because so far it's been fun. Thanks. Kathy
     
  13. Dec 5, 2011 #13

    paul52446m

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    In your pic. you have a fan switch with 3 or 4 wires going off to the right. Those wires go to another box about 6" sq. There is a lot of wires in that box. take the cover off that box and take some more pic. Paul
     
  14. Dec 6, 2011 #14

    slownsteady

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    Hi folks, I don't have any answers, but i have a suggestion.

    Paul, since it sounds like the problem started when the thermostat was changed,maybe it would be good to start there. It certainly would be simpler to mess with a couple of wires at the stat.

    Kathy, I know your friend has hesitated to call in a technician because of the cost, but after burning fuel for a month, it might be less expensive than letting it run.

    Just a couple of thoughts...
     
  15. Dec 6, 2011 #15

    auntybb

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    Hi, Paul,
    Will do. I'll get back to you.
    SBS, the thermostat was changed because the problem had already happened. She turns off the power to the fan to shut off the fan, so the furnace doesn't run constantly.
     
  16. Dec 6, 2011 #16

    tflatebo

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    Make sure your filter isn't clogged. The easiest way to do this is to remove it.
     
  17. Dec 6, 2011 #17

    auntybb

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    Hi, Paul, Here are the photos, although I wasn't able to remove the cover of the case because there is another square thing with wires on top of it. If these don't give you enough information I'll send more. Thanks again.

    HPIM3770.jpg

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