Gas and Oil Home Heating Furnaces - Hamilton Furnace Problem

I've got a Hamilton Model PBKM-LD20N140C that isn't "kicking in". I have checked power to the unit and is 120 +/-. There is a regular power switch installed inline. If I turn the power off, then back on, an LED blinks once on a label title Diagnostic. It says that one blink is LOCKOUT - CHECK FURNACE.

What does this mean? None of the fans start so of course no fire gets lit either. Sometimes, when I turn the switch on you can hear that it almost tried to turn a fan on, but no go. With the switch on, I can hear a VERY faint hum (almost like a relay or seized motor). The blower fan spins freely. Any ideas? This is the first time this winter I fired it up.

If the furnace has an intake or exhaust blower, it is probably stuck. Try taking it off & turning by hand. Some you can use a small screwdriver to turn it without removal.

Thanks chief! It is now flashing "Pressure switch stuck open". How can I locate this? There is a disc shaped thing with what looks like a vaccum tube coming out that goes into a small motor. Is that it? Any way to fix it or just replace it?

Try the old tap-tap with a screwdriver handle. Tap, not pound.

OK, here is what I have found now. If I hold the switch and alternate having it closed and open, I can get the ignitor to glow, then I have to alternate it manually (or the ignitor will go out) and it starts to flow gas. At this point the fire looks like it comes up pretty high and touches some of the wires. Is that normal? It only does it for a second or two and then shuts down completely. Am I in trouble?

I might add that you can blow on the hole (or draw) and the switch does go in and out. I'm not sure though if the pressure is controlling the voltage or if the voltage is controlling the pressure???

My guess here is that the fan isn't blowing and that isn't creating a vaccum, which doesn't trip the switch, and doesn't draw the flames. Is that correct?

Pressure is controling the voltage.
For some reason, you do not have air flow thru the furnace.
Take the vent pipe(s) apart to make sure nothing is blocking them. I've seen wasps build a nest & completely block the pipe.