"Bad switch? Furnace is only a year old and this has never happened before".
Do you realize how ridiculous this sounds:B
Using this logic, AN RV OR NEW APPLIANCE WOULD Never have a warranty type problem under its warranty?????? Just because the furnace is new does not keep a Hi limit switch from failing. FYI, Hi limits DO have a higher than normal failure rate. But, they usually stick OPEN and do not allow the furnace to operate at all. Now, one thing you mentioned in your first post was the OILY substance in the area of the old Furnace solenoid. THAT should have been addressed BEFORE you did anything else. Replacing the Regulator was NOT the only thing to do. IF you have the OILY contamination, especially downstream at an appliance, Where do you think the oil came from? It came from the LP tank. It ruined the regulator and you now have that oily substance thruout your LP line system. You may need to flush your LP lines, but I would concentrate on the line from the furnace to the main pipe manifold under the RV. Doug