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  1. #1

    Confused Cold Weather Furnace Problem


    I live in an a later 1970's manufactured home with a Intertherm MAC 1199 furnace. For a couple of years I have had the following problem with the furnace.

    Initially the regulator went bad and it was replaced by a local HVA contractor. The contractor told me that the exact replacement part could not be purchased any longer but they could adapt a modern regulator. The HVA contractor installed new regulator and the furnace seemed to work just fine. There was a much more pronounced window rattling start ignition but everything seemed just fine.

    However, ever since the new regulator was installed the pilot goes out when and only when the temperature drops below approximately 20 degrees!

    The HVA contractor came out several times and kept turning up the pilot light. The problem persists and the HVA contractor now on longer returns my calls...

    So I have personally replace the thermocouple and made sure that I have a correctly adjusted pilot flame. The gas company tells me that the pressures are correct.

    This morning I woke up to a very cold house and 18 degrees outside.

    The VERY interesting thing I noticed this morning when I went to light the pilot was that my long neck lighter kept blowing out when I put it into the access door to light the pilot!

    In fact there was a very pronounced draft running into the little access door. Enough air flow such that I could not maintain a flame on my lighter when placed just outside of the access door nor could I strike a flame on the lighter if it was inserted into the pilot area!

    Once I had a fire going in the wood stove and the sun came up (warming the roof?) I went back and the air flow into the furnace was minimal, the lighter could strike a flame when in the furnace and the pilot light worked perfectly!

    The furnace has been running fine all morning and I am REALLY STUMPED!

    Am I nuts or what?

    All info and comments Greatly Appreciated!


  2. #2
    Join Date
    Jan 2008
    I would have it looked at by a qualified contractor.
    You're getting into dangerous territory, and there is not much we can do to help you through a computer screen.
    And since it is a standing pilot, I'm assuming it's the original unit, beyond normal lifespan, and would seriously consider replacement.
    "Hey Lama, hey, how about a little something, you know, for the effort." And he says, "there won't be any money, but when you die, on your deathbed, you will receive total consciousness." So I got that goin' for me, which is nice. - Carl Spackler

  3. #3
    Join Date
    Aug 2009
    Beatrice, NE
    Do you set your thermostat back at night? Does this problem happen during the day or just over night? Did this ever happen before the regurlator was changed? Natural or LP?

    First, my guess is that the draft through the pilot lighting hole decreased because the wood stove was pulling enough air from the house that there wasn't enough left to cause exesive draft at the furnace. Wood stove suck a lot of air from a house.

    2nd, I think you pilot problem is associated with the mini explosion in the furnace when it lights, it should be fairly smooth. You need someone to check why you have delayed ignition, the technical term for the mini explosion. If it is mainly a problem after you have turned the stat down, my guess would be that the delayed ignition is blowing the pilot out when the stat is turned down. Do not try to fix this yourself, many experienced tech have lost eye brows on these problems or worse.

    My experience is that it will get worse so you need to get it fixed. Don't be suprised if it takes a while to cure as many times once it lights and the furnace warms up even a little it won't act up again till it cool down.

  4. #4
    Thanks for the replies!

    Adjusting the pilot light back-off from the maximum pressure actually stopped the booming starts. The pilot light was roaring like a jet engine...

    And I will not try to fix the furnace myself as that is way above my skill set!

    The house was a fixer-upper and very poorly maintained when I purchased it. What I am wondering is where the combustion air comes into the furnace? Could the furnace intake be clogged up and forcing the furnace to try to vent right past the pilot light and through the access door? And how could the cold cause this problem of venting the combustion air?

    Thanks for your thoughts!


  5. #5
    Join Date
    Aug 2009
    Beatrice, NE
    There are a lost a variables that affect the draft through a furnace, cold being one of them.

    I remember a manufacturer seminar where an engineer said combustioni was a black science because of all the conditions that affect it.

  6. #6
    Join Date
    Jul 2004
    I can't troubleshoot your problem from here but with a standing pilot issue, I've had considerable success of the years with an automatic relight kit. A pro can easily install it if that's all it will take to solve the dropped pilot issue. Or you could have a good pro diagnose the real problem. Or you could upgrade to a modern unit without a pilot! Pilot boilers and furnaces in our area haven't been allowed for new installs since 1986. So...we don't have so many anymore.

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