FIXED Prove switch closed prior to activation of combustion air inducer.

[MaximumSquid]

Model Number

100973-01 0609N0

Brand

LG

Age

6-10 years

Solved. . .
Link to the manual for the Lennox furnace control board: manualslib.com/manual/1077334/Lennox-G40uh-X.html?page=36#manual

Number on the board in the furnace:
100973-01 0609N093634 1012-969

From the manual:
DS1 LED (RED) = OFF
DS2 LED (GREEN) = ON "Flashing Slowly"

Prove switch open.
OR: Blocked inlet/exhaust vent;
OR: Prove switch closed prior to activation of combustion air inducer.

Last one turned out to be true.
To bypass this you will need rubber gloves on. Turn the furnace off and unplug the pressure switch.
Turn the furnace on and when the combustion blower turns on plug the pressure switch back in and you will have heat until it turns off again.

I will need to replace the pressure switch, but I can run it manually like this for the moment.

 

[Dan O.]

What was/were the actual symptom(s) or the complaint that you solved??


Dan O.

 

[MaximumSquid]

It was actually three things.

The thermostat had a bad on/off switch. (Replaced with new)

The Pressure switch was made before the blower started which gives the error highlighted above.
You can start the furnace with this unplugged and then plug it back in to get it going in a pinch. (New pressure switch rated for "0.85" on order)

Lastly the thermocouple needed to pulled out and cleaned. This worked for a few days. Now the thermocouple is not sending enough juice again. (Only 200-300mV)
I will likely need to buy a new one. Still looking.