Hi all, and welcome Vhaalen,
Water heater electronic ignitors have been is use on Airstreams for over 15 years. One consistent problem I see that regularly repeats itself here in the PNW is spider webs in the combustion tube. The heater will not light as the presence if even small webs apparently disturbs the air and propane mixing properly. Many an ignitor module or control valve has been replaced I think when the webs were at fault; that includes me once many years ago. I have learned to always disassemble and clean my heater burner tube any time the heater has not been used for more than a few months and does not light off properly; for years this has always worked. I also blow out the big tube with compressed air as well.
This can happen to full timers who use the AC rather than Propane as with no pilot light to cremate them, the spiders will migrate to the warm spot and weave away.
. Fall seems to be the worse time for this.