The house has two furnaces: one for the basement and main level and one for the upstairs. This is good because apparently furnaces are like Jaguars: you need two so you always have an operable one while the other is being repaired. These are high efficiency furnaces, which necessitates a power vent--the Achilles heel of furnacedom. Because these units are so efficient, they combust the natural gas more completely and also extract more heat from the exhaust gas, so, without getting too technical, the result is liquid water in the flue pipe. This water drains back down the pipe, by design, through the draft inducer blower housing and down into the floor drain, after passing through a number of hoses and plastic fittings. Therein lies the problem.
As a safety feature, there are magic switches that know when everything is not ducky in the furnace and shut things down. These switches are so magically endowed as to sense even the slightest little problem. In other words, they are as moody as a teenage girl. If the condensed vapor (liquid water) does not completely drain out of the inducer blower housing, the inducer fan blades pass through the water, consequently slowing their speed, causing the blower to draw more power in order to keep up. The magical sensors see that the blower wants more power and throw a hissy fit, shutting everything down. You wake up cold.
The fix is simple; you just have to clean out the fittings and hoses. What, you may ask, could be clogging them up? I have it from an actual trained technician that the offending matter is dead bugs. Having cleaned out black gunk from the hose fittings, I can neither confirm nor deny this. The matter is simply unrecognizable to the naked eye in this form. I will say, though, that it is tenacious. I had cleaned out the fittings and hoses only days ago, leading me to think that a beast of a different stripe was afoot this time.
Observing that the furnace was igniting and burning for a period of time, then exhibiting flame quality issues and ultimately limiting out, I was gunning for the gas valve. Logical, right? I mean, I just cleared the drain lines. And besides, if the inducer housing was full of water, the furnace should never ignite at all, right? I consulted an expert. At first, he agreed that the gas valve was the culprit. But on further discussion, he suggested that it might be that the sensor in the inducer housing was PMSing--flipping open and shut, overly sensitive to the realities of everyday blowing conditions. In my world, this kind of erratic, unpredictably humanistic behavior from inanimate objects is perfectly normal.
Preparing to do internet-galactic battle with online appliance parts vendors, I donned my minor's cap and delved deep into the bowels of the furnace in search of the "Secret Magic Talisman" that would ensure victory. This "Talisman" is protected by various traps and camouflage designed to obfuscate it's secret location to even the most stalwart homeowner. I had inoculated myself against treacherous conditions by imbibing an ancient elixir of hops and barley. Emerging unscathed, I heard a muffled cry from my favorite red flannel shirt, mortally wounded...brave soul. The red shirt always gets it. No time to mourn--I started for the computer with my prize: the serial number.
But something clicked in my head. It wasn't a blood vessel. This time. Like Obi Wan, a voice came to me: "Abuse the furnace". So I kicked it. But there was more. A lifetime of implausible circumstances flashed before my eyes with an accompanying score by John Williams: new replacement parts bad from the factory, dropped screws lost in pants cuffs, pinhole leaks in new copper plumbing, beads of solder that looked just like dropped ball bearings, bad ground connections--lots of bad ground connections; the images taunted me. But the message was clear--do not rule out the absurd. Yoda chided me: "Do or do not; there is no try". I bitch-slapped that little Muppet.
But I could not deny that, as often as not, the problem lies in a previously ruled out scenario. So I checked the hoses and fittings again. This time, I took a critical elbow fitting completely out of the furnace and down to the shop. Blowing through the fitting produced an air stream out the other side, but it was a little weak. So I fired up the air compressor and decided to put 120psi through that little orifice. Sure enough, what must have been the mangled body of a very crusty bug shot out the small end of the fitting and pinged a piece of sheet metal leaned up against a wall. "Inconceivable!", I said out loud. And that was it. After all that, the problem was that I had done a half-assed job of cleaning out the dead bugs in the drain line.
It occurs to me often that when something as common and predictable as a bug can stop the furnaces of the world, that perhaps the engineers are a little arrogant when they decide on tolerances. I mean, what is the point of making a drain line orifice so small that a dead bug can clog it, especially when the clog results in a failure of the entire system? Just asking.
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