Thermostat Confusion or Perhaps Just Ignorance

There should be a transformer on the wall near your boiler (square metal block about 2″x2″ with two wires coming out of it).  It might have 24V stamped on it somewhere.  If not, for $15 you can get a multimeter and check it yourself.  The same transformer could in theory be used to power the 3rd wire and your new thermostat.  It would be cheaper to buy a battery operated thermostat than to hire a pro to rewire for you.

northofditmas

in Boiler Repair 13 years and 9 months ago

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hamiltonheights | 13 years and 9 months ago

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I thought I had a 24 volt, 2 wire  oil/steam heating system: my bolier is connected to my electrical system (it has its own circuit breaker). But, when I tried to replace my thermostat with a fancier 24 volt model, the new thermostat could not find any power. So could I have a millivolt system?  My old thermostat, afterall,  runs on batteries. But it seems, however, if my reading is correct that the millivolt would run off a pilot light (which my system does not have) via a thermocouple. At teh same time I have traced the wiring to the controls of the boiler & have not been able to identify a transformer One final piece of information, there is a third wire that isn’t used in the current setup. Is there a way to definitely tell if I have a 24 volt system? I appreciate any help..

eman134 | 13 years and 9 months ago

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you probably bought a three wire thermostat….your old stat was simply an on/off switch which needed it’s own power (batteries)…the wires were power in,power out, no common leg to power up the new stat