Analog thermostat went binary.
January 1, 2010 10:55 AM   Subscribe

Why has my thermostat gone binary?

Living in an old (turn of the century) apartment building with gas heat. My heater works fine, but my thermostat doesn't -- the heat NEVER turns on, unless I set the thermostat to the max, at which point the heater starts to fire and stays on continuously until I turn it back down. It's just become cold enough to make this a real problem at night.

Needless to say, the thermometer on the thermostat shows a much lower temperature than any setting, but that isn't sufficient to get the heater going.

Bonus: I bought a replacement (digital) thermostat, but I can't turn off the power to this one for some reason -- none of the switches in my breaker box seem to control it. Help?
posted by zvs to Home & Garden (10 answers total) 1 user marked this as a favorite
 
I only know a few basic things about thermostats, but it sounds like the bimetallic coil is broken. You might want to open it up and take a look.
posted by Johnny Assay at 11:05 AM on January 1, 2010


thermostats are not too expensive... I would ask them to replace it... or, replace it yourself...
posted by HuronBob at 11:07 AM on January 1, 2010


When you replace the thermostat, please make sure the old one is recycled, they often have quite a bit of mercury in them.

And, put in a programmable thermostat, which will make life more pleasant, and save energy/money. I am not very DIY, but I was able to replace my theremostat.
posted by theora55 at 11:11 AM on January 1, 2010


The thermostat is clearly broken. Most thermostats are low-voltage, and can be changed safely without shutting off the power. The thermostat probably gets its power from the furnace itself; flipping the breaker / removing the fuse for the furnace typically shuts off tstat power as well.
posted by jon1270 at 11:11 AM on January 1, 2010


oh, sorry, didn't read the whole question. I think it's un-powered, and there's no breaker. IANAElectriciab.
posted by theora55 at 11:31 AM on January 1, 2010


There is service switch somewhere near the furnace that the service people use to shut it down while working on it. There should be an emergency switch typically with a red wall plate, at or near the entrance to the where ever your furnace is installed; f/ex, near top of the cellar stairs, on the garage wall if your furnace is in there, etc. Either switch will shut off the furnace and allow you to change the thermostat.
posted by TruncatedTiller at 1:55 PM on January 1, 2010


Best answer: 1) Your thermostat is broken.
2) If the heater doesn't have a fan you might/probably have a millivolt thermostat system which is why you can't find a breaker to shut it off. This style of thermostat isn't interchangeable with standard thermostats.
posted by Mitheral at 4:47 PM on January 1, 2010


Response by poster: Yeah, upon a little research it's a millivolt system. Weirdly though, when I take off the thermostat and touch the wires together, the heater doesn't start, which seems wrong to me.
posted by zvs at 6:20 PM on January 1, 2010


Best answer: Millivolt systems are working with such little power that even the two layers of oxidation on the wires can cause the circuit to malfunction. Plus the thermopile could be dirty, they often are after years of use, which lowers available power. Try twisting the wires together instead of just touching.
posted by Mitheral at 12:08 AM on January 2, 2010


Response by poster: Future readers: it turns out that the thermostat was broken AND that in the process of removing it, an internal breaker in the furnace tripped.
posted by zvs at 4:27 PM on January 7, 2010


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