Atwood model 8531-Iv-dclp furnace

What is voltage where trailer wire goes into furnace?

Is the fan turning/air flowing-- assume so since gas valve is opening?

I have 12.6V coming to the control board. The fan is running and the air flow is good. The LED on the control board is green until it tries to ignite. Then it turns red during the ignition cycle.

I am wondering why you replaced the circuit board? If you are measuring the voltage to the spark probe when it fires very low as the service manual lists that as a "high tension" lead and does not specify a voltage but it is in the 1000V or so range. They do advice not to attempt to measure it.

I suggest that you download a copy of the service manual from the site of Bryant RV and study it.

Electrode is out of adjustment
Electrode is faulty
Electrode high tension wire is bad
Bad or loose ground

I suspect your electrode is bad

Here is a service manual that covers your model......LINK