Gas Furnace Experts. Question for you on jumping the limit switch

swimman Posted By swimman, Dec 8, 2008 at 11:32 PM

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  1. swimman


    Sep 19, 2008
    Rhode Island
    Long story short, the limit switch on my Lennox gas furnace is bad. Can't get one for a day or two. I put everything back together the HVAC company took apart and jumped the limit switch. Should I be concerned with doing this or am I ok? What are the consequences? Should have a new one very shortly.

    Thanks in advance.
  2. R&D Guy

    R&D Guy
    New Member

    Apr 25, 2007
    Well I don't do furnaces but I know that the limit switches in gas fireplaces are there to keep your home from burning down if the fireplace is on too long. I'd say you are putting your home and family in great danger. The purpose of the limit switch is likely so the flue, or furnace doesn't get too hot and cause a fire. Bypassing this safety feature can cost you more than your home, this could cost you your life.
  3. PaulRicklefs

    New Member

    Sep 24, 2008
    La Ronge, SK Canada
    As a professional gasfitter I'll never recommend bypassing the limit. On the other hand I've done it in a pinch.

    Depending on where the limit is, (burner compartment or flue) determines level of danger. Are there more than one? Usually newer furnaces have 2-5 limits in different areas to sense flame rollout or plugged venting.

    What I would do is keep a close eye on the furnace, purchase a CO detector if you already have one and sit tight. There is usually a reason for a limit failing such as repeated flame rollouts or negative pressure in the house so I would be very concerned with that.

    Short answer is no, it's not a good idea. Long answer is you gained a working furnace, while certainly raising the level of danger in your house.

    Try using your electric oven for heat for a day or two, much safer.
  4. Redox

    Minister of Fire

    Feb 23, 2008
    Burbs of B'more, MD, Hon!
    I would only do it for "testing" purposes only. How long that "test" lasts is up to you. If the furnace fan were to quit, it could get ugly. I wouldn't leave the house or go to sleep with it jumped out. Then again, I wouldn't be able to sleep anyway.

    Every company I've worked for would have canned me if I did that.

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