I found this (reference furnace problems) link on irv2.com
Furnace doesn't light - iRV2 Forums
"Worked this up when My furnace quite.. NOTE: In my case it was the very well named Mother board (Control board) that was bad. I opted for a Dinosaur board replacement.. Glad I did. Very well built here in the USA buy folks who take pride.. And even the design is better.
When the T-Stat calls for heat the control board starts the blower (1)
The blower blows closing the sail switch (2)
The control board then opens the gas valve (3) and begins sparking (4.1)
Gas Flows (5) And ignitets (4.2)
The flame heats the flame sensor (5)
The flame sensor sends .480 volts to the control board (6)
which then detects the .480 and continues operation (*)
When the T-stat says "Enough already" (RV is now warm)
The control board shuts off the gas flow (*)
and then turns off the blower after a cool down (*)
see page 2