Lennox 90% Furnace - Please help troubleshoot

Discussion in 'HVAC Heating & Cooling' started by Opifex, Oct 29, 2019.

  1. Opifex

    Opifex Member

    Sep 12, 2019
    I have a Lennox high-efficiency furnace that is operating fine with the fan set to "Auto" on the thermostat, but if I set the fan to "On" then the low-pressure switch always fails to close (Code E227) and the furnace will not fire up. Please advise.

  2. WorthFlorida

    WorthFlorida The wife is still training me.

    Oct 28, 2009
    Orlando, Florida
    Is this a new problem or always had this issue?
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  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    Where does your system get its combustion air? If your ductwork is not well designed and sealed, it could be trying to suck room air in and messing with the static pressure in the furnace room. Similar to combustion air. If it's not pulling in from outside, the combination of the two fans, the induction one in the furnace and the blower, could be upsetting the pressure.

    Also, look carefully at any rubber hoses to ensure there aren't any splits or cracks to the switch(es) and gas line. Check any fittings as well, as the plastic might crack.
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