Along with many others we have a Dometic RMD8505. In our case it was retrofitted sometime before we bought it. We ve just had a problem on gas, runs perfectly on 12v or mains was sparking but would not reliably fire on gas. I have recently replaced the whole burner assembly so pretty sure that was good. Big problem was that I had forgotten my multimeter and only had one of these voltage pens with me but realising there were many useful threads on the same subject, I began to suspect the control box, happily I managed to locate one in nearby Irun so went to get it. sadly the problem remained. I got the solenoid valve off and it looked pretty clean, thought about running a wire to the solenoids but not sure whether it was one of these low voltage trigger affairs, anyway put it back on and gave the end of it a tap with the screwdriver while sparking, and instant success and its worked since. I'm obviously going to source a new solenoid asap but thought I would share this as it might temporarily get someone out of a problem.