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jennifer3333 t1_jc2k7ub wrote

Question: I have a boiler (1972) and the gas co is offering me a new programmable thermostat but I have tried this before and failed. Someone told me I need a third wire from the furnace to make this work. Any body familiar with this situation?

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Trixeth t1_jc45tjp wrote

Generally you need a common wire.

Old tstats were basically switches.

New tstats need a power circuit in addition to the switched outputs.

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jennifer3333 t1_jc6pvif wrote

Thank you. I bought the basic $29. version of Honeywell and have it working already. But I would love a programmable in the future. Thanks for the response. Now I know why the ones in the past did not work.

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