Holiday Rambler Travel Trailer Water Heater Troubles

Be sure you have water in the water heater tank before you do anything. The on/off on the water heater is for the electric heat element. It only works when you are plugged into shore power. The water heater switch by the sink - probably has a red light next to it. That is for using the heater on gas. It needs 12V to ignite, is your battery charged? Is it possible that you are plugged in and the electric heat has the water hot enough that the gas doesnt need to fire?