This brings to mind that many of us overwinter our rigs near or at our homes where in order to keep them at the ready we don't winterize them fully. That means for me at least that when freezing weather hits, especially during winters like this one where it's been constantly off and on, I go out and turn on the HydroHot and one interior thermostat to 40 as threats loom, then off as ambient temps warm. I prefer to rely on the electric only so the fuel tank remains topped up, minimizing moisture absorption therein over the often unforeseen, unintended, long storage periods.
Due to one or two similar experiences to Dan's over the decade we've had the coach, I now don't just go in and flip on the Electric element switch. Rather I turn on the Diesel switch first, then the Electric, then switch off the Diesel. This ensures any prior fault is reset since that's one function of the "master" Diesel switch besides winding up the burner motor. I come back later and double-check in the bay that the unit is warm and all lamps are green.
It's a good routine to get into whenever you aren't high-demanding the system with hot water use and need only minimal heating, whether in storage or on the road.
Joel