Stop guessing if you need to take your RV into a service center, answers are here in this tutorial video. Learn how to maintain the water heater on your RV.
You can locate the water heater by looking for a panel with a vent/grill looking box on it on the outside of your unit. Be aware that the vent/grill could be Hot! To open up the compartment you just turn the little knob on the top, and it should open right up. Located inside should be the control board which is a little black box. If your water heater is not working you want to check the connection on the control board and make sure it securely connected. You can unplug this and make sure it is not corroded on both the sides of the connections. Go ahead and just plug it back in after you have checked. Next thing you want to do is check the igniter, make sure it is fully plugged in with no corrosion as well. The next thing is to check the Diode; you can check this by "bypassing it". You just unplug it from the board on both sides and then just plug it in directly to the board. If it still doesn't work then you need to start checking your LP to make sure it is turned on, and make sure you have a 12 volt power. If you have done all that and it still does not work, then you need to take it in and have it serviced. If it's trying to light and it's not lighting you need to check your burner assembly, what happened here is rust will build up, bugs could get in there and build nests. So get your can of air out and spray inside there and make sure it is clean and then you can try to light it again. After all that it should light up, if not you will need to take it in to be checked and repaired. To maintain this, what you want to do is take out the anode rod once a year. What this does is keeps the corrosion from building up inside your tank. Corrosion will instead build up around the rod and eat it up. Once the rod is 75% corroded you need to change it out. Replace it with this instructional RV video.