Yes, that would argue against boiler fluid.
Another test point would be amp draw. Pay attention to the AMP load before you turn on the burner, and then see how it changes with 1 burner then 2.
A shorted or bad heating element will be "open", and therefore amp load will not increase. Same will be true if the wire became disconnected (aka: burned up).
A properly running electric heating element will be 10-13 amps of usage. Test with 1 element, and then test with 2. Make sure each climb up in usage.
**BEFORE DOING THE FOLLOWING - TURN OF ALL AC & DC POWER TO THE COACH**
For more detailed testing, open the cover and expose the electrical ends of the heating elements. Disconnect both wires so there is no circuit to the heating element. Then with a multimeter test the resistance between the 2 connectors. Properly working should be in the range of 10-30 ohms.