I would start at the basics.
- Turn off the water supply and water pump.
- Open the hot water faucet in the trailer and let the pressure bleed off, then close the faucet.
- Open the heater door and feel the pressure relief valve to see if it's warm/hot.
- If it's cool, open the relief valve and see if water comes out.
- Leave the relief valve open and turn the water back on. Does water come spewing out of the relief valve?
- Close the relief valve and go into the trailer.
- Make sure the stove lights and burns for about 10-15 seconds.
- On the monitor panel turn on the water heater gas switch.
- Does the stitch light up?
- Between the gas and electric switches on the panel is a fault switch. Is the fault light on?
- Leave the gas switch on and go out to the water heater. Is the burner on?
- Above the burner but below the relief valve is a wire with a clear plastic tube around the wire. Is this clear tube burned/melted?
- I think there is a fuse on the front of the heater. Is this fuse burned? Maybe replace it just to be sure.
If something is not right, let us know what you found. Also can you get to the back of the heater (maybe under a bed) and see if everything is hooked up?
On the electric side it's possible that the previous owner ran the electric side of the water heater with no water in the tank. If that happens the element burns out pretty quickly and it will have to be replaced.