Click here to Find a Contractor in your area.
In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
Need to contact us? Visit

Lennox G26 Furnace - Limit Switch Open

Mike BMike B Member Posts: 155
Also check the heat rise through the system. Info should be on the rating plate.


  • StefanStefan Member Posts: 1

    We just moved into a home with a Lennox G26 Forced Air Furnace. Been having a problem the last couple of days where the gas is shutting off after running 5-10 minutes. The LEDs finally gave a code of "Primary/Secondary Limit Switch Open". After cycling power, the furnace starts working again. What should I do to troubleshoot? I couldn't find a service manual anywhere online.
  • Tom KTom K Member Posts: 26

    check the air filter to see if it is clean. If that is clean then inspect the blower wheel for dirt on the fins. A 1/16 of an inch will reduce efficency by 25 percent. I have had problems with that heat exchanger cracking prematurly. Get a Carbon Monoxide detector.
  • Ken D.Ken D. Member Posts: 820
    Lennox G26

    As already mentioned, check air filter,and blower wheel. Make sure the blower motor is not over loading and shutting off on overload due to defective motor or capacitor. Make sure flue passages are not restricted or the vent is not blocked. Does this furnace have a stack damper of any kind? It may not be opening properly. Sensors may be weak or a bad connection in the circuit of same. Make sure the duct supply registers are not closed or the returns not blocked. I don't remember if this is a condensing furnace, but if it is, the condensate may not be draining properly, or the secondary heat exchanger may be restricted.Hope this helps.
  • Water in Exhaust blower

    has been a problem on these. If you do a search for "Lennox Gas Furnace G-26" you will get some good information and the availibilty of a PDF on the manual for the unit.
  • DeanDean Member Posts: 8
    Lennox G26

    The G26 is a condensing 92% AFUE gas furnace. The limit switch will trip typically when the temperature rise exceeds the range listed on the rating plate. I am a Territory Manager for Lennox in the Midwest (Indianapolis). Can you tell me your complete model and serial number- I can get you the unit information manual. Also, the last digit in the model is the most critical, we call the "dash number".
    Several things can impact temp rise, gas firing rate; air flow; typically we find air flow issues are the main reason for excessive temp rise. This could be as simple as dirty air filter, dirty blower wheel, dirty or plugged secondary heat exchanger, and dirty evaporator (A/C) coil. Anything that will decrease airflow will increase your temp rise.
    If you want to find a local Lennox dealer, go to and look at our dealer locator for a dealer near you.
    Let me know if I can be of any other assistance.

    Dean Meece
    Territory Manager
    Lennox Industries- Indianapolis
  • Dean Meece, I attempted

    to find a service manual for the G26 and was only able to find Homewoner information. Is there a service manual available and if so how does one get it. I was trying to help this gentleman with his problem and a PDF download of a service manual would be very helpful.
  • DeanDean Member Posts: 8
    G26 furnace

    If I could get the exact model number, I have all the unit information, installation and service manuals and would be glad to forward them to you. The most important digit in the model number is the dash number, the last digit. ( ie. G26-Q3/4-100-2)

    Let me know.
  • DaleDale Member Posts: 1,317
    Temp rise

    As the other post suggested check the temp. rise. This is on the nameplate on the furnace, probably something like 35 -70 degrees. then measure the supply and return temp, subtract and the number should be inbetween perhaps 40. If its near 70 there's not enough air flow. If there is an ac coil it acts like a air filter and can be blocked with junk on the bottom. The condensing cell on the bottom also acts like an air filter, you remove the blower to check if the inlet to the condensing cell is clean. There are more things to check but a Lennox tech needs to be called, prehaps you have a homeowners warranty.
  • Chris ReakChris Reak Member Posts: 20

    I have quite a few service manuals on this unit. If you want one, e-mail me your mailing address.

    Chris Reak
This discussion has been closed.


It looks like you're new here. If you want to get involved, click one of these buttons!