My Furnance has stopped working
This is a condensing furnace. It has a two stage heat exchanger. The first stage are those big S tubes in the top of the furnace. The second stage is below and there should be a drain from the secondary heat exchanger that runs into a trap. Clean out the trap and the drain line.
You have the power off at the breaker box right? I just looked at the schematic and it looks like your pressure switch is supposed to be normally open. Take a look for yourself.
Anyway what should happen is that the inducer (Exhaust) motor should go on when the stat calls for heat. Air flow should close the pressure switch and initiate the ignition sequence. The igniter should glow or spark or whatever yours does, and the gas valve should open pilot, and then main gas.
Check to see if all your vacuum lines are good, not cracked etc, and if they are not, you should call a good HVAC tech to go over your entire unit, because you have gone about as far as you want to go. Pressure switch, Igniter and Flame sensor is about my limit, but maybe somebody good will happen along, at least you got the obvious things out of the way.
You do change your filter regularly right?
" A lot of men build things, and a lot of things fall down "