...In which Nathan struggles with a left-handed thermocouple and wins, then gets to school a doomsayer for his encore.
As a short-term fix, he'd duct-taped the critter in place, which provoked this response:
"Geez. When the water heater blows and launches through your roof, I wonder if it will look like the contrail in LA last month."
Nathan for the win: "It can't blow. [...] See, a thermocouple is a dielectric generator that puts out a couple of millivolts of electricity when it is heated (e.g., by the pilot light). It is connected to and holds open a normally-closed solenoid valve. If the pilot light goes out, the electricity stops, and the valve snaps shut, cutting off the gas. It does, in fact, fail safely, which is what happened when the thermocouple went bad[...]."
Yep. No moving parts. No external source of juice. Heat it up, it makes electricity; cool it down, it doesn't. This is true no matter if the lack of heat is from the pilot light going out or the thermocouple falling out of its awkward, backward threads. (And if you think that's fun, the ancient coal-converted-to-gas furnace in my house in Collegetown even ran the thermostat on the thermocouple voltage; talk about failsafe! And it would run and heat the house, albeit without forced air, even when the power was out.)
I don't know when it became popular to assume that all household appliances are monsters teetering on the brink of explosion and that all American men are hapless boobs when it comes to fixing them, but it's not true. It's funny in sitcoms because it's not true.
For the record, I vote with Nathan: left-hand threads on a common thermocouple is just stupid. I'd be very tempted to note the backwards threading on the water heater with a Sharpie or a paint pen.
1 week ago