The fix ended up being a reset of the thermostat. I had to remove the cover of the aqua-hot (model 450-DE) and then remove a junction box cover to get to the thermostat reset. It was a very tight fit in there, more so than the attached picture, but there is a little white button that needed pressed to reset it. I pushed it a number of times because it didn't feel like it moved so I was skeptical this would work but it did. Attached is a picture of the location of the reset button (item #2).