Keeprite NG furnace code "fail to ignite"

If the ignitor heats up, it is surely OK. Flame sense is not active for a few seconds of flame.

The sequence, depending on the type of furncace:

1...Call for heat activates the control board/ ignition module, certain safety switches must be closed, AKA over temp, plugged vent, vent spill, etc.

2...Module fires up draft blower for a certain time, then commands igniter to come on. It is timed for so many seconds, and you should hear a "click" when the gas valve opens.

3...When the gas valve is commanded open, the burner should ignite. There is several seconds delay to allow the burner to stabilize, and to obtain a flame signal

4....The flame detector works like this: The flame rod/ flame detector works by what is called "flame rectification."

The rod (may be the ignitor itself, or a separate rod) is fed a fairly high voltage, around 100V AC, current limited signal, and when a good solid flame is present, the flame itself rectifies the AC similar to a crystal radio, and a circuit in the ignition module, detects a tiny DC current, down in just 1 or more microamps.

I would study the circuit carefully to see if there are any safety switches in series with the gas valve, and then rig a meter "backprobe" into the gas valve solenoid (s). There are many times two valves for safety. After the igniter has been on you should read 24AC at the gas valve terminals, and if the solenoids are working, should hear and feel a "click" as they activate.

ALSO if the solenoids seem OK, CHECK INCOMING GAS PRESSURE. Or do you? have another working appliance, such as range, dryer, etc?