At around 3AM on Friday morning one of my smoke alarms (in the loft) went off. There was no sign of smoke, and no smell. I checked out the entire house and the garage but found nothing out of the ordinary. I figured a false alarm, which I have had once before with that unit.
On Friday night I was watching TV with the kids and could very faintly smell something burning. It smelled a little like fried electronics but was so faint that I wasn't that confident that I was really smelling anything at all. I checked the entire house (for the second time) and couldn't find a thing.
The next day there was finally a distinct (but still faint) smell. At this point I was starting to guess that an electronic component burnt out on something; that smell does tend to linger for quite some time. I thoroughly checked the TV, assorted players, laptops, ceiling fans, pot lights and even went around the house smelling the receptacles and switches, a loose wire arcing perhaps.. everything appeared fine though. I was getting a little worried that I didn't have a clear source of where the smell came from/was coming from.
The wife and I were going out overnight on Saturday. She had already went in with the kids and I was just starting to get ready when I noticed a very faint bit of smoke highlighted by the pot lights in the kitchen. When I focused closely on it I could see that it was "moving" past the light rather quickly. I hopped up on a chair and opened the vent that is above the pantry, I could finally smell it quite clearly.
I went down into the basement and opened the air exchanger, the motor was humming but the fans were not moving. There was no immediate smell. The unit has fresh air intakes and is sealed up pretty good when the insulated/gasket'd door is closed. This is why I couldn't smell anything in the basement! I unplugged the unit and when I removed the rigid Styrofoam insulation that encloses the motor I could see that the running capacitor on it was already beginning to melt. Even with a gloved hand I could feel the heat radiating from the motor, the back of the unit itself was also warm.
This is what the inside of the motor looked like. As you can see the wires are beginning to melt (they are stamped at 125C). The annealed motor wirings where they pass through the casing are protected by some form of plastic? material. In most places it was almost completely burnt off. The Styrofoam panel closest to the motor was also starting to melt. Close call indeed.
As for hindsight? I did get a pretty good hint that should have clued me in on Saturday morning. While washing the dishes I was looking outside and noticed that the window was a little foggy. Hmm.. this could only happen if I filled the sink with scalding water (I hadn't) or.. if the air exchanger wasn't working properly!
These are just words >