Yes, the problems can often be the circuit board as it has to make several decisions in the process of getting the burner lit.
Knowing what to expect is a big part of finding the cause.
The process for many is this:
1. We turn the thermostat on heat. That sends the signal to the furnace, leaving things like bad contacts, etc. in the thermostat itself or bad connections to the furnace.
If we know where and what change should happen at the furnace, we can test to make sure it is happening!
2. The blower should come on. That is when RV and home furnaces are different as a safety item. In RV they do not open the gas valve until there is full air flow as a way to avoid filling the RV with gas!
When air is flowing well, the "sail" on the sail switch moves and closes a microswitch. The sail may be stuck on spider webs, etc. So having a manual to tell us where those wires to the switch are found can save us pulling the furnace out on some! We can put a meter or the wires and look for change when the airflows!
3. The timing built into the board starts and it either gets positive air or it times out and shuts down! This is where I feel you may be on this one.
4. If it gets good air, it lets the rest go forward. It may heat an igniter and then open the gas solenoid or it may have a "clicker" type ignition which we can see/hear start.
5. Finally the gas opens and we should see it light!
If the flame senser doesn't get a flame, the gas valve closes and doesn't fill the furnace with gas to blow up!
Minor differences in some heaters and certainly different boards and connections make me look for info. That info on hand lets me go through and check , starting with the item where the whole train stopped.
It seems tedious and lots of people do skip over getting the right info but I find it very easy to miss some tiny obvious item that takes me much longer to find and fix than I spend getting the right info.
One of the big failures I find at RV repair shops is the people are often semi-familiar with all the different items on RV but not really of the sort who want to go into knowing exactly each items on hundreds of different RV. And they tend to be less inclined to go look for details but often turn out to be "part changers"!
It saves them time but it also costs us money because we still pay for the parts even if there was only one bad! They also tend to change a part and say it fixed things when the real problem may have only been bad connections on that part.
Putting on a new part is ONE way to get clean connections! But not the one I like to pay to get!
In your case, it can be the sail switch is stuck or bad.
It can be the board is bad and the signal is ever sent to the sail switch. OR it can be the wire between the two points is corroded and a good wiggle of the right connection may fix the whole problem.
By nature, RV tend to have more corrosion problems than our cars. First they have lots more and second we may leave them setting for longer to let the corrosion build up more before we drive them to wiggle those connections and break the corrosion build up!
