RV Furnace Troubleshooting Basics | DoItYourself An RV furnace has an internal sail switch that will prevent the machine from igniting in cases of air flow being insufficient for combustion. As a result, the vent will work, but no heat will be produced.Author: DIY StaffFan Does Not Run but Furnace Still Produces HeatIf you notice that your machine is still giving off heat yet the fan is not running, there are several sources you can check. Heat means that there..Fan Does Not Work and Unit Produces No HeatIn this case, you need to first make sure that the battery isn't dead and that you have twelve volts to the furnace. Even if these check out, elect..Fan Is Running but Furnace Produces No HeatAn RV furnace has an internal sail switch that will prevent the machine from igniting in cases of air flow being insufficient for combustion. As a.. RV Furnace Basics and What to Look For | RV Repair Club Much like a house furnace, an RV furnace has a central spot that creates the heat and a series of ducts or tubes that carry the warm air into the various parts of the interior. This basic design exists whether you’ve got a large motor home or a smaller trailer version.