Hi and welcome to FixYa. I am Kelly.
There are 6 things that can cause this condition. 3 No Spark and 3 Spark observed.
No Spark
1. Spark Plug Gap
2. Defective Transformer or Ignitor
3. Cracked Spark Plug
With Spark
1. Pump Pressure
2. Restricted fuel flow due to:
a. Seal Leak
b. Filter Blocked
c. Nozzle Restriction
3. Fuel Filter Restriction
Download this manual:
http://www.desatech.com/techDocs/DESA%20SPARK%20PLUG%20IGNITION%20SERVICE%20MANUAL.pdf
Go to the pdf file page 11 for the test procedure. Start with the "Observed Fault."
You may not be able to check step 4 per isntructions but, if you have fuel pressure is should work.
Read step 5 carefully before proceeding with work on the fuel nozzle. (page 12)
In step 6 Note there is a fuel filter in-line. (page 13)
WIRING DIAGRAM IS ON PAGE 23 OF THE MANUAL.
Clicking on the www at the bottom of the pdf pages will bring up a parts link.
This should get you going.
Thanks for choosing FixYa,
Kelly