RV Repair: Suburban NT45S furnace not igniting, winnebago chieftain, pressure gauge

Question
Hi,

I have a Suburban NT45S furnace on my Winnebago Chieftain which is not
firing up.  It did about a week ago, after several attempts.  I tried today with
no luck, though.  Here's the details:
I turned on the gas, lit a burner on the stove to be sure everything is working
right with the regulator, even started the gas fridge to be sure.  The fridge
took a few tries, but eventually lit itself fine.  
When I switch on the thermostat, after about 5 seconds the fan kicks in on
the furnace.  There is also air movement at the intake/exhaust vents outside.  
(I bought this used, so I don't know if it's up to full power or not, but it seems
reasonable.)  
After about 15-20 seconds, I hear a click, which seems to be the gas valve
opening.  I tested this once by turning off the main gas valve and watching
the pressure gauge used to check for leaks.  When the click happened, the
gauge dropped by about 1/3, then stopped there.  The drop and subsequent
stop were very abrupt.  I'm also not really smelling any gas, so it's certainly
not continuing to run gas out.
I pulled the red wire off the igniter and held it about 1/8" from its plug.  It
did not spark.  Power is good - I tried with the generator on, I have two
batteries which are fully charged, one of which is brand new.  
So, is there anything else I can try, or does it boil down to a bad board?  If it
is the board, is there any way to get at it without disconnecting everything?  

Thanks!
Tony

Answer
Tony, If the motor is running and you hear a click and see that it is the valve opening then that indicates that the motor is turning fast enough and that the limit switch is telling it that it is not too hot. The power starts at the relay and then goes to the motor and the sail switch. From there it goes to your limit switch and then to the board. In order for the gas valve to open the board has to get power to it and this can only come from everything allowing it to get there. I have seen in some cases the electrode getting a crack in it and the spark being sent to ground and therefor not igniting. But if you held the red spark wire and it didn't bite you then I would have to say that the board is bad and needs replaced. When you do replace it I recommend using a Dinosaur Igniter board. If this furnace continues blowing cold air even if the furnace won't light and you want to make it stop blowing when it doesn't light then I would use the "Fan 50 Plus" board by Dinosaur. If this is an older coach then it will have a regular igniter board and not one that controls the fan, but everything you would need to do the upgrade comes in the box with the upgrade board. Oh and Tony about having to pull this furnace, well there is no other way that you can get to the board. Sorry this is not what one would want to hear. I hope this helps, Bill