In my 2007 Georgetown 391, I've got a suburban gas furnace (not sure which model, but one of: SF-20F to SF-35F) controlled by a DuoTherm thermostat - this one has three switches - (cool, off, furnace) (fan on - auto) (fan hi-lo) and a sliding temperature control. We've just set out fulltiming and have encountered our first nippy weather - at night we use only the front furnace or A/C unit and that keeps the bedroom temp fairly constant while the heater or A/C cycles on up front. For the last two nights, it's gotten down to about 50 degrees, and with the thermo set to 65 degrees, we hear it working as we go to bed, but wake up to a pretty cold 58 degree temp inside. Moving the switch from "furnace" to "off" and back to "furnace" gets it going again, and all seems OK. The fact that it comes on immediately indicates that the set temp is indeed above room temp, and the thermostat knows it. So my question is: what might explain the system seeming to work fine, but not coming back on again after cycling off because the set temp is reached? Since it happens during the night I really don't know whether it happens after the first cycle, or just some time later... We really need to figure this out because we plan to be in Colorado in a few weeks and will need to leave the unit for a couple of days with the furnace(s) running to keep it warm. As far as I know, the rear furnace works correctly, and the front furnace has seemed to work correctly in the past.