[hbens]

TJ mine was operating with the same gripe you have. Diesel just decided not to fire up and I used electric to heat the water. Fast forward a few weeks and my AH boiled out some from the overflow bottle overnight. It got extremely worse when I drove the coach. I pulled all fuses from the AH and that remedied the problem until we got home. We had enough hot water to shower in the mornings from the engine heat the day before.
Short story long I didn't want to just throw parts at it and had it serviced along with another issue I had. My back is in sad, sad shape right now so I can't do all the things I usually would do. They put a troubleshooting box on it and determined the thermostat was the issue. They also replaced and fuel nozzle and what goes with that part of the service.
I'm tempted to spend the money on getting one of those troubleshooting boxes instead of just throwing parts at it in the future.
I did ohm out the 4 components from a troubleshooting matrix and they appeared good.
Short story long...it works as it should now. Yours may be the same component issue. Mine was an intermittent issue that didn't show up under normal probing.