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High limit switch open on armstrong furnace

I have an Armstrong Air furnace that is not blowing hot air. Noticed the LED light is flashing four times, which, according to the alarm code means I have a high limit switch open. Turned the furnace off and back on but that didn't do any good. How do I find and manually close/reset the high limit switch??? Thanks!

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  • Anonymous Oct 21, 2008


  • almercer670 Dec 14, 2008

    new 90plus eff. goodman furnace......4-flashes h-l-o, there seems to be 2 or 3- limits,which one is problem,,,ok to bypass?

  • bradlytdot Dec 19, 2008


  • Anonymous Dec 23, 2008

    it's supposed to be as simple as a reset button--how do you do it on a york diamond 80

  • A_Artanis Dec 26, 2008

    Same thing - no hot air, LED flashes 4 times. Where is the stupid switch, what does it look like? I have Ultra V, Tech 80 model of Armstrong Air. It's Boxing Day, everything is closed (of course!), it's -30 outside.


  • John Ferrell
    John Ferrell Jan 18, 2017

    Hey, I love your question that asks how to manually reset the high limit switch. I'm sorry to hear that turning the furnace off and on didn't work. Recently, I have noticed that my furnace hasn't been acting up. I think that hiring a professional might be a good choice when looking for the solution.

  •  John
    John Jan 18, 2017

    An "open" on a high limit switch could possibly means it's defective and needs to be replaced. Or you may have a clogged filter or some sort of defect or obstruction in the blower's squirrel cage that's triggering the high limit switch to "open". A furnace is at risk from overheating anytime the air flow is restricted; so When the high limit switch "trips", the heating element will shut-off but the blower will continue to run to cool off the heat exchanger. If you have no experience with troubleshooting and repairing HVAC system, hire a heating specialist. Remember, the high limit switch is a safety device- don't mess with it if you don't know what you're doing!


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If you know where the high limit switch is you can always cut the two wires and wire them together causing the limit to close. But what you have to watch out for is why the high limit is not closing. That means in your return air either you have a dirty return air duct, dirty filter, or you don't have all your registors open to allow the heat to escape the heat exchanger. Just watch over riding the system. The high limit switch should either be on or behind the blower, in the middle of the system right under the heat exchanger. any other questions about hvac just ask.


Posted on Jan 17, 2009

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You need an ohmmeter. Start checking all thermal limit switches
and fuses. Remove one wire when checking and also turn voltage off to unit. It could be a resetable switch, start pressing all the pop up buttons on the switches.
The cause could be simply - dirty air filter or a blower assy problem, or dirty flue vent, or induce draft fan problem.

Posted on Mar 23, 2008

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I have an Armstrong high efficiency 90+ Condensing Gas Furnace. The Blower works on Cool, but not when the Heat is on. The LED flashes 3 times: Fault is Pressure Switch open with inducer on"

Where is the combustion blower? Is this an easy fix?


Posted on May 12, 2010

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The limit switch is one of several built-in safeties designed to protect the furnace and prevent a possible explosion. Rule # 1, i.e. don't put jumpers or do any other things that you don't fully understand as it is extremely dangerous to play with furnaces. Remember, you are not a certified HVAC mechanic. Rule # 2, i.e. read the manual and follow simple steps such as find any blockages, open closed registers, etc. Rule # 3, i.e. if all the above doesn't help, don't be a frigging idiot and call a professional !!!!!

Posted on Dec 29, 2009

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