18F. That's chilly! I was awake a little before 4 listening to the creeks and groans of the settling in the trailer period and the furnace coming on and off. The furnace and the electric blanket were keeping me nice and toasty and Dexter snuggled up with me. I drifted back to sleep then I woke a little before 6. It felt cool in the camper but warm under the blanket so I read for half an hour and then began to wonder why I didn't hear the furnace coming on. Dexter needed to go out so I got up to investigate. The temp in the camper was 40 degrees and no furnace action in sight! I took Dexter out and we saw that the reading on the propane tank said empty. I knew I was getting to the end of one tank and had a full tank on the other side. Normally the valve automatically switches over and start using the full tank when the first one runs out. I flip the switch to show the indicator the full tank and it should have turned from red to green indicating it was now sensing the full tank. The indicator stubbornly remained red. What was going on? I knew I had filled the tank and worried that it was malfunctioning. I turn the valve at the top of the tank and found that it was closed. Once opened the indicator turned green as it should. Back in the camper I increase the thermostat temperature and waited for the furnace to kick on. I waited, and waited, and waited, but nothing happened. I turn the thermostat all the way off and then back on again and waited. Nothing happened. To be sure propane was coming through the lines I lit a flame on the stove and was relieved when it jumped to life right away. After trying to cycle the thermostat on and off again the only other option I could think of was the fuse to the furnace. After a bit of wrangling, I managed to pull the blade fuse from the panel. when I did, a red light came on on the electronics board. Since that light was not on, I suspected the fuse was probably okay and reinserted it. That did the trick! The furnace clicked on and hot air began to blow from the vent! Success! I'm relieved to have the heat working and it always feels good to solve a problem. Dexter and I are crawling back under the electric blanket for a little while for a little while until the camper warms back up.