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    cnckelsey's Avatar
    cnckelsey Posts: 2, Reputation: 1
    New Member

    Oct 24, 2006, 06:06 PM
    Thermostat Wires don't match-help please
    Sir or ma'am-

    I am attempting to replace my 1960's era Honeywell thermostat with a modern 5-1-1 and I managed to thoroughly confuse myself.

    My 1930's era house only has gas heated radiator system connected to this thermostat. We added central air 6 months ago but it is on a separate system. The old Thermostat had a clock in it that was powered by two wires.

    Coming out of my house is Black, White, Blue, red and Green.

    The Honeywell Thermostat has C, G, Y, W and Rc RH.

    FYI if it helps, The old plastic plate says Heat On- R-B Heat Off R-W

    I am not sure what this means but any help connecting would be appreciated. I had to use portable heaters because the heat isn't working and the kiddos are cold!
    labman's Avatar
    labman Posts: 10,580, Reputation: 551
    Uber Member

    Oct 24, 2006, 06:51 PM
    Usually there is a 24 volt AC transformer in the furnace with the secondary winding connected to a red wire running to the thermostat and a blue wire, common, to the gas valve, A/C relay, and fan relay. From the thermostat there will be white wire to the gas valve, yellow to the A/C, and green to the fan. The thermostat is wired to switch the power from the red to the white, yellow, and green as needed with the blue completing the circuit. Most thermostats and furnaces have the contacts labeled R, B or C, W, Y, and G for the corresponding wire colors. It may be wired to have the A/C control wires return to the furnace and its controls and then a second wire goes to the A/C unit. Internal wiring may replace the green wire if the thermostat does not give you the option of fan only or continuous fan. Digital or programmable thermostats may need the blue wire connected to them.

    The new thermostat should follow the above colors. It will not use the G, RC, and Y since they are for the fan and A/C which you don't have. You may need to go to the boiler and verify the red comes straight from one side of the thermostat. Connect it to the RH. Determine if the black or blue comes the other side of the transformer and connect it to the C. If the blue was connected to the gas valve as the old plastic plate suggests, disconnect it and connect the white to it. It is possible the old thermostat had a double throw switch in it connection the power to something to shut off the heat at the end of the cycle. If so, unless the directions for the new thermostat explain how to use that function, you will need to add a double through relay with the coil powered by the wire from the W terminal, and what starts the boiler connected to the NOC contact and what shuts it off connected to the NCC terminal. The common will need power either from the W terminal or directly from the red wire.
    cnckelsey's Avatar
    cnckelsey Posts: 2, Reputation: 1
    New Member

    Oct 25, 2006, 03:18 AM
    Thanks for the reply!

    I looked at the transformer on the boiler and it has a blue wire coming from it. So I connected the blue wire to the "C" on the thermostat and am not using the black wire now. I just put electrical tape on the end of it. Your quote"If the blue was connected to the gas valve as the old plastic plate suggests, disconnect it and connect the white to it." Does that mean I should take the white wire and connnect it to the C connection on the thermostat? Where would the blue go?

    As you said, since I only have a boiler system I don't need the Rc (which is jumpered to the Rh) or the green wire. Do I need to take out the piece of metal connecting the two R connections or is it OK just to leave the red wire in the Rh even though it is still jumpered?
    Also, is there any reason NOT to connect the green even though I am not using it to keep it out of the way?

    But my basic hook up now is Blue-C; White to W; Red to R. Not using Black, Green.

    Willl let you know soonest if it works. The house AND family are cold and not happy with Dad!

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