A not so hot post

Perhaps, I forgot to include in my previous post from Florence that we had a malfunction of Sadie's furnace on that trip.  This problem is the gift that keeps on giving.  On our very first outing with Sadie, the furnace fired up and worked fine, until we went to bed. Then, the fan continued running, but there was no fire. It turned out there was about a cupful of bees and other flying things in the combustion chamber! I cleaned them out, and the furnace worked fine for a couple of years.

The next failure was at Potlatch, WA.  We were enjoying a fall retreat by the beautiful waters of Hood Canal, but we were not enjoying any heat from the furnace. That one was a little more complicated.  After removing the furnace and going through an exhaustive diagnostic process, I determined that the high-limit switch, whose job it is to make sure the furnace doesn't overheat, had failed.  That is not to say it failed to keep the furnace from overheating. On the contrary, the switch physically malfunctioned, which prevented current from flowing to the control board, which controls all functions of the furnace. That is the long way of saying the failed switch didn't let the furnace light.

Now to our current problem.  I must admit that the current problem is, in one way, less daunting than the previous ones. That is because I have now had enough involvement with the furnace to know how it is supposed to work.  I felt confident in going through the troubleshooting process this time...until, that is, I could find nothing in particular wrong. 

Well, that is not precisely true.  I did find that the furnace wouldn't light (no, duh!), but all of the circuits, switches, etc., checked out fine. I found that, on the bench at least, she went through the proper sequence for start up.  1) Thermostat calls for heat; 2) after a few seconds' delay (normal), the fan came on; 3) next, the sail switch closed, allowing current to flow to the circuit board; 4) after a few more seconds, the direct ignition electrode began to spark.  The one thing I couldn't determine for certain was whether the gas valve opened.

I concluded that, since there was spark, the failure of the furnace to light, when it was in situ, could only be attributed to a lack of gas being delivered to the burner.  The third element necessary for fire, of course, is air.  I knew there was plenty of air, because the sail switch, whose job it is to make sure there is adequate air to support clean combustion, closed, allowing the process to continue to the spark phase.

What I wasn't sure about at this point was what might be causing the lack of gas getting to the burner.  Since Jill wanted to make a trip to Salem, I decided to consult with the folks at Roberson RV.  A gentleman there (I'm not sure he was even an employee) walked me through the process for checking the gas orifice and valve function. I performed those checks today, including running some steel wool through the gas pipe to clean out any loose rust, followed by some air through the pipe (but not through the orifice itself, against which I was summarily warned). 

Now I know that the valve opens and closes on cue, and the gas pipe and orifice are clear. Theoretically, the furnace can't not work now. I didn't reinstall the furnace, because I wanted to paint some areas where rust had got a foothold on the furnace housing.  I sanded and painted the areas with Rust-o-leum, so I will wait for the paint to cure until tomorrow.  Then we will see if I am a competent furnace geek.  Stay tuned.