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    needHVAChelp's Avatar
    needHVAChelp Posts: 1, Reputation: 1
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    #1

    Feb 9, 2016, 08:10 PM
    Lennox g40uh error. Furnace won't heat
    Lennox g40uh error "Primary or Secondary limit switch open"

    I have test the continuity on both limit switches and on the flame roll over switches. Along with a few other things. Could it be the control board?
    ma0641's Avatar
    ma0641 Posts: 15,675, Reputation: 1012
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    #2

    Feb 9, 2016, 09:31 PM
    Found this in the manual under troubleshooting. The ignition control is equipped with two LED lights for troubleshooting. The diagnostic for that code is: LED #1 slow flash, LED#2 is on
    "Primary or secondary limit switch open. Limit must close within 3 minutes or unit goes into 1 hour WatchGuard." That is what you are getting? Did you check the high limit?
    Are you locked out in the Watchguard?
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