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Furnace starts, but no heat nor fan operation.

Hi, my furnace went out yesterday. It responds to the thermostat, but starts up without any heat, nor the fan. I called a repair guy, he's amazed it still runs for it's age. But, for the ten years I've had. I've never had a problem with it. He believes the lies with what he called the "transformer". Black box, bottom left, bout 3" square x2.5". What do you think? And, is it possible to get parts for this model anymore? lol


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  • motobaby Feb 07, 2008

    Ok, after reading my post and responses, I did not realize I was in air conditioners, and I don't know how to post to "Furnaces", although I'll try.

    Anyways, in respnse to Jimfl, I don't know how turn on the fan switch on the thermostat. But, what happens when I turn the thermostat on, is I can hear that the furnace "kicks" in. Sounds normal, as if starting up. The pilot is lit, but does not change from it's lit position. The flame does not get any bigger. I will try to learn and understand what you are suggesting. Thanks.

    In response to "thespark", It's a 1978 Intertherm Gas furnace, model 1378. Responds, meaning that when I turn up the thermostat, the furnace sounds as if in normal operation, except there is no heat, nor fan operation. The furnace does not blow any heat, and does not get hot itself.

  • motobaby Feb 08, 2008

    Hi, and thanks. i spoke with repair dude today and mentioned what you people are suggesting. Repair guy claims he's 100% percent it's the "transformer" as he claims to have troubleshot it and says it has power going to, but not (24V) coming out. I hope I got that right, but that's what I understood, (as this power is needed to open and close the gas valve?). He says that part is obsolete. I live in Northern Alberta, Canada, bout -25 now, -45 the night it went out. But he thinks he can build one, power module/transformer.


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If youe burners fire off it's not the transformer. It suonds like the fan/limit control. Try to turn the fan switch on the thermostat to the on position and see if the fan comes on, if it does leave it on and turn the heat on and see if the heat works that way. If so it would be the combination fan/limit control.

Posted on Feb 07, 2008

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Please move this to furnaces..
When you say "responds" you mean what?
I hate doing this, but....
gas or oil, what do mean by respond? etc...

Posted on Feb 07, 2008

  • B Helling Feb 08, 2008

    Hmmmm... So it makes SOME kind of noise, but the fan does not turn, and the main burners do not come on.

    The "transformer" is undoubtedly a simple 24vac or 26vac one...

    Known in a previous life as a "doorbell transformer". Shouldnt cost that much. HOWEVER... you need someone with a voltmeter and patience to go over the furnace, carefully!

    (Ok Im guessing, the model # mean nadda to me.. if this is a 2 year old high efficiciency thing with circuit boards and whatnot, the xformerbox is gonna be mucho more,,,)


    Last time I ran into something like that, I was about to replace the xformer, until I tested to see if IT was getting 110V.. Nope...

    But it was hard wired in

    Traced wire back.. 10 feet away, inside a junction box on the ceiling, the twist-on connectors (marr connectors) had come loose and the connection was sparking...

    Ok.. no real fire hazard, was in a metal junction box (and thats why they should be), but could have ripped the whole furnace apart for a new xformer and still had no luck..

    So.. Its all very straightforward.. IF this is to work, its gotta have that..

    Make sure the xformer has power going into it, and nothing coming out before replacing it..

    If uncomfortable with voltage that can maim you, get someone you trust..



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