Lennox 90% Furnace - Please help troubleshoot

[Opifex]

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.

Thanks,
Y.R.

 

[WorthFlorida]

Is this a new problem or always had this issue?

 

[Sponsor]

 

[Jadnashua]

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.