Any of you who live in the tundra like myself, here is something to think about if your having problems with furnace when the temp drops to near 0 temperatures.
Went out to repair a unit today at customer's home. Temp was 12 degrees daytime, near 3 at night. Unit was locked out when I got there, Ignition lockout according to code. I reset computer, fired it up and it attemped to start 4 times. Would fire, then go right out. Forced vent motor, fine. Pressure switch, OK. Flame was lighting up on 2 of the flame tube orifices.
I suspected either bad gas valve or low gas pressure. Turns out, very low gas pressure. Upon talking to someone, they said moisture in gas lines which ends up in the meters causes the meters to freeze, and deliver low pressure. Furnace was fine once gas company came out and put on new meter for customer. Something for you guys to think about when servicing in these cold temperatures. May not be the unit itself.