Hi, I just want to offer a couple of thoughts to help with your problem.
1st - To confirm you have water in the heater - You can:
- Open the pressure relief valve located on the HW heater while it is under pressure and see if you have a good flow or;
- Remove the annode and confirm it was full.
2nd - If no water is in the tank:
- Open the foward left cargo compartment (just forward of the HW Htr on the 2604
- Remove the panel perpendicular to the rear edge of the access door (1/8" square drive bit should do it). This panel provides access to your water heater valves, pump etc..
3rd - you will see red and blue lines that feed the water heater.
- There is a ball valve on each line that opens or blocks flow to the HW tank for use during winterization.
- If you want Hot water then ensure both valve handles are in line with the lines (open) and the valve on the bypass line (between red and blue is closed.
- If, by chance you've been heating an empty tank, I hope you have done no damage.
4th - I also have a 2011 2604 and I use both gas and electric as I find it provides quicker recovery. If I'm concerned about propane, then I use only the electric but it is notably slower.
Last - I have no idea of your level of RV knowledge or mechanical ablity, so please don't take offense at anything I've said.
Best of luck