Furnace Failure and Working Backup Plans

Negative 18 degrees for a low is a bad time for a furnace to go out in any domicile. Depending on heat from a breakable system of fans, control boards, ignition systems, switches and relays is a recipe for an eventual critical situation. In an RV, the situation is slightly different because the walls are 1.5” thick Styrofoam and only retain vital heat for so long. Since I just experienced this situation, I realized it was a story worth telling. Thankfully, through all of my planning and forethought, I had backup plans in place that allowed me to experience this calmly and without damage.

The Suburban SF-30 furnace that came with my RV failed on a frigid February morning. It actually silently failed overnight, but I didn’t notice until the evening that day. The only way I noticed was that the cabin was a couple degrees colder than normal when I came home and the furnace didn’t appear to be firing. The only way the cabin wasn’t stone-cold was that I have electric heaters with thermostats that come on at a finely tuned temperature. With the electric heaters as a backup, everything was saved.

The furnace failure was quiet, but marked by obvious signs – signs which I caught onto quickly and responded to. The signs were a cooler than normal internal temperature and no sign of furnace firing when it should be. Once I realized what was going on, I entered into my first phase of emergency backup plans. The only way my first layer of backup plan was different than what I was doing anyway was to install a small, personal heater in the water compartment under the bed, so the internal water pipes didn’t freeze. The rest of the cabin was warmed by electric heaters on a supplemental basis anyway, so this one step was quite simple.

Since I realized the failure around 6pm on a February night, it had already been dark for an hour and was already quite cold – negative 11 or so when I checked. In my preparedness, I pulled on my arctic-insulated Carhartt bibs, a fleece coat, an expedition-weight down coat, a wool hat, and wool glomitts. This insulation was necessary because the furnace is accessible only from outside. I grabbed my volt meter to test relays and power to the motor, and a few other tools, and started testing the device. Before I put on my deep-cold winter gear, I looked at the manual and came up with theories for what was wrong first – the schematics give enough information to get an idea of how the device works and what could be wrong.

Truth be told, it took me a while to narrow down what went wrong, but that first night spent outside until 10pm in negative 18 degree temperatures allowed me to begin forming hypotheses to test the next day – mostly, it gave me an opportunity to familiarize myself with the device and to sleep on my experience.

The next morning, I went out and started testing my hypotheses with a written plan of things to test. I even came up with theories for what tests would determine what part(s) were the cause of the failure. Once I found tests that were falling into my range of theory of what was wrong, I was able to start gathering parts that needed replacement. My theories were pretty rough estimates at best, largely because I was unfamiliar with this device and how it worked – I had never seen the internals of the furnace before, or any RV furnace for that matter.

My tests revealed that the “time delay relay” was likely out due to a failed voltage test with the thermostat on and calling for heat. Then, the motor simultaneously was not showing continuity where and when I hypothesized that it would have continuity. Whether the motor was actually bad is something I didn’t actually care to test further – the motor was likely original and almost definitely on its last legs anyway. The furnace in my coach is 15 years old this year and I have put year-around-dwelling pressures on it. As a 12 VDC motor, it was likely to go bad any time.

Upon finding the likely candidates for failure, the next phase was to figure out how to extract the guts of the furnace to work on it and to locate parts. My location doesn’t have a parts dealer, so I had to go to the nearest city, over 40 miles away. The commuting time for such travel added roughly three to four hours to an already long day, which included a lengthy diagnosis and learning period already.

All the while, I learned that each propane-dependent device did not have its own shutoff valve. That meant that if I wanted to service the furnace, my water heater and stove become non-operational. In a full-time living situation, that’s not practical or safe. So, another project got added into the mix: The project of adding a shutoff valve to the furnace’s propane line. That also meant learning how to do this correctly and safely.

The cold snap that both triggered and increased the severity of this failure led me to have to learn systems quickly and to pick up new skills fast. I had to learn how to make flare fittings in copper gas line, how to properly install gas fittings, and how my furnace worked in order to get the right parts. Being able to pick up these skills fast was critical, but was underlain by a long history of working with vehicle electrical and mechanical systems that made these skills fast and easy to pick up.

Safety in this case was critical. Working with gas lines and valves becomes dangerous and I can only hope that I did it all as well as I think I did. Failure to set new gas fittings properly could lead to explosive consequences, which I believe I avoided by doing my work right. I suppose time will tell.

In the end, the lesson is that it is always good to have backup plans on top of backup plans and to respond quickly and effectively to these kinds of critical failures. When I rebuilt the furnace, I made sure to clean every part, lubricate anything that moves, and to preemptively replace something if it is destined for failure. The blower motor and the time delay relay had to be replaced, which required a nearly total disassembly and reconditioning of the furnace. The time delay relay was even discontinued, but I was saved by the presence of an aftermarket model that will likely outlast the original by a number of years. In the end, I spent hours outside in sub-zero temperatures, but was never uncomfortable or concerned for my safety through extensive preparation for such an event. I had hoped that I would never have to see such a circumstance, but now that I have, I realize that my preparations were fantastically appropriate and that it could have been worse and I would have been unscathed. That’s a pretty incredible statement considering the complexity of the job and the weather extremes that I was faced with.