Hi Al,
One of the ways that I use to isolate an intermittent issue like that is this. With the wabasto unit cold, remove the unit so you can have access to the nozzle. Purchase 2 feet of 1" clear vinyl tubing from Ace hardware. Put the tubing over the nozzle and the other end in a bucket. Next put a piece of tape over the photo electric cell next to the nozzle. Have someone turn on the unit while you observe the ignitor probes for spark and diesel flow into the clear tubing. This will prove the start-up cycle. This is a dangerous test so be careful. If you are not comfortable, have a qualified RV technician with wabasto experience perform it. My guess would be the ignition module. Hope this helps, Fred