Wait. That’s not a dust ball…
Several weeks ago as Curly was getting ready for work she noticed that the house was a little cooler than usual. She didn’t think much of it as she and Bee hurried off to work and didn’t think about it again until she got home that evening. She adjusted the thermostat, as usual, before she started dinner, but realized several minutes later that she hadn’t heard the furnace kick on. The house has an old thermostat that makes it easy to turn up the heat without actually noticing what the temperature of the house is, so she went back into the living room to look at it. What she found was that the house was 52 degrees and the heat would not turn on. Grrr. She realized it might be a long night. After checking the hot water to be sure the gas was working, she called Bee, who was on his way home from work. He called the owner of the house, left a message, and when he got home went to the basement to investigate.
Bee is a mechanical engineer and naturally very curious about the way things work, so he secretly enjoyed the challenge of figuring out what the problem with the furnace might be. Meanwhile, Curly was upstairs with a space heater in the kitchen making dinner (macaroni and cheese, which is baked in the oven, thereby warming the kitchen a bit more).
At some point Bee came back upstairs to tell Curly he had made a startling discovery. He had taken the front panel off the furnace to look at the control panel and of course it was pretty dusty and cobwebby in there. He looked down at the bundle of wires and thought, “That’s a really big dust ball. Hmm. Wait a second… That’s not a dust ball! Eww!”
It was a mouse. Tangled up in the wires. Very stiff. Very dead.
Turns out that the mouse had nothing to do with the malfunctioning furnace. The problem was the flame ignitor, which had a crack in it.
After years of very intense heat, they finally give out and crack, which prevents the gas from being lit, depriving the furnace of any heat. (Our furnace doesn’t have a pilot light. Instead, the flame ignitor heats up and ignites the gas each time the heater kicks on.)
This is Bee again. The ignitor is a resistive coil that quickly heats up and ignites the gas. I ran a diagnostic after I installed the new part and I got to see the furnace run through its entire cycle, it was really quite fascinating. First it turns on the air; at this point 4 gas jets start then the coil heats up to ignite the gas. (note: the 4 jets of gas are pretty exposed and are at eye level when you are working on a furnace, the jets look like little trumpets (diffusers)). There is a flame sensor that will trip once the gas ignites (the flame sensor looked like it was just a thermal couple but I didn’t look at it too closely). At this point the whole system waits for the thermostat to say the room is up to the desired temperature then the furnace will shut off. In our case the thermostat is an older mercury switch that sits on top of a coil. As the metal of the coil shrinks or expands due to heat the coil will seem to rotate since one of the coil ends is fixed. This rotation then causes the mercury switch to trigger the furnace. Studying systems and controls I got to read a lot about this sort of thing but this was the first time I ever really got to play with a system and its controls (that’s what you get when your degrees have the word ‘theory’ stuck in them…I digress), so I had a blast. Needless to say I immediately wanted to improve this system. Unfortunately my constant reassurances that I could dismantle any improvements I made and restore the place to its original condition didn’t work on Curly…sigh…
Well, it was too late to get the part, so Curly and Bee warmed their bedroom with a space heater that night, and the next day the owner of the house got the part so Bee could put it in during his lunch break. Curly and Bee were happy because they didn’t have to wait for a repair man to come fix the furnace, and the owner of the house was probably thrilled, because he only had to pay for the $30 part, instead of a repair man.
…and Bee was happy to now have a space heater for the garage for working on his car…