The main things that shut down the flame after ignition is -
flame sensor is coated and does nor recognize flame thus shuts unit down.
pressure switch faults due to extra pressure in the system, but if properly vented, no obstructions, or bad switch it should be fine.
Limit trips, but this is after an extended run where it overheats.
The flame sensor trips in 3-5 seconds
Pressure switch trips upon firing
Limit trips after extended run
The vent motor drawing 3 amps is on the 120v side of operation and the flame/ignition control is on the low voltage side. So even if the motor were to amp up, as long as the transformer is still delivering 24v to safety circuit and ign control it should be fine.
My first bet is flame sense. Sand the sensor off and if I am wrong I will remain available for follow up
is this a hot surface that glows and lights pilot and then pilot lights burner
this is the honeywell smart valve.
change the circuit board
This is like saying I have a noise in the tires somewhere and I changed 3 and it is still there. There is only the pilot assembly left. And also you do have the board in the valve but also the board controlling power to the valve and the inducer assembly in the blower section. You say you have changed the gas valve, the circuit board, and a pressure switch but the code is not pressure switch.
There is only one component left.