Probably the Thermal cut off. You can pull the Thermal cut off off and just plug the brown wire in to see if that fixes the problem. There not cheap to replace, I spent $30 for a 2 pack of the things. I ran my water heater a few days before I replaced the Thermal cut off but its a good idea to get it replaced sooner then latter. I ended up routing mine a little different as it was hanging down very close to the flame tube and I assume that's why mine popped as the trailer was less then 6 months old and had only been used 3 times when mine went.