How long between flame on and off? YES, it is normal for a LOT of RV's. Because the OEM did NOT install the ducting to Furnace install specs. This causes the Hi Limit switch to kick in and out during the cycle. The furnace overheats due to the lack of adequate ducting to remove the heat from the burner chamber. So, as other have suggested, an RV furnace it is NOT a good idea to clock off some duct covers to get more heat to another area. Even blocking just one duct cover will cause this. Most common cause is the round 4 inch flexible duct hose in kinked or smashed somewhere inside the floor or cabinets, if the ducting is installed to furnace specs. Doug
