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    greg0081's Avatar
    greg0081 Posts: 1, Reputation: 1
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    #1

    Jun 17, 2009, 01:24 PM
    Wiring a rth221b honeywell thermostat
    I have the honeywell rth221b thermostat and coming out of the wall I have red white green yellow and a blue they all match the thermostat except for the blue wire not sure ware to put it the thermostat has a rh rc white green and a yellow ports
    wmproop's Avatar
    wmproop Posts: 3,749, Reputation: 91
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    #2

    Jun 17, 2009, 07:55 PM
    Blue is probably common, used to run the stat instead of needing batteries
    Isn`t really needed if you have a battery operated tstat

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