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    New Thermostat for 3-wire System

    An_Fo
    An_Fo Member Posts: 2
    in Radiant Heating
    I'm trying to update my thermostats around the house. They currently are old mercury-powered White-Rodgers, and I'm just looking to step up to anything newer.

    The problem I am having is that the new Honeywell I put on doesn't turn the boiler off.

    I have three White-Rodgers zone valves, and from what I can tell, they need a longer signal to start closing than just the thermostat stopping the heat call.

    The old thermostat ran off of three wires: red, white, and green.

    Touching the red and white together calls for heat, and the valve opens.

    Touching the green to red for more than 5 seconds closes the valve. Any amount of time shorter than that, and I can hear the valve start to close, but if I release the wires, it doesn't continue closing.

    With the new thermostat hooked up ( red to R, White to W, Green to G), when I stop the heat call the valve does not close, and the boiler just runs continuously. I've tried moving the wires to various other positions to no avail.

    Am I missing something obvious? Are there other thermostats that might work? Other positions that I should try for the wires?

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    Comments

    • JUGHNE
      JUGHNE Member Posts: 11,392
      What is the model number of the new HW tstat?
      Do you have a wiring diagram showing heat only, series 20, using 3 wires? Then you go to installer set up for more directions.
      An_Fo
    • An_Fo
      An_Fo Member Posts: 2
      Thank you, your questions led me to the answer. I need a SPDT t-stat, which the model I have is not.
    • JUGHNE
      JUGHNE Member Posts: 11,392
      Simplest I know of is HW FocusPRO 5000 series. TH5110D1022.
      Non programmable....might not be in the big box stores.
    • ChrisJ
      ChrisJ Member Posts: 16,641
      JUGHNE said:

      Simplest I know of is HW FocusPRO 5000 series. TH5110D1022.
      Non programmable....might not be in the big box stores.

      The 5000 can behave as a double throw switch? Disconnecting W and connecting something else?

      Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.

    • ratio
      ratio Member Posts: 3,969
      Some of the cheap heat pump stats have a form C contact for the reversing valve, but the internal logic might not allow it to work. Best bet would be to add a simple single pole double throw relay powered from the W terminal. That would convert the signal to what you need. Another option might be a Honeywell TrueZONE panel, if you have more than one zone. The outputs of the zones are form C.
    • JUGHNE
      JUGHNE Member Posts: 11,392
      According to the paper.....tstat R goes to valve R.....tstat Y goes to valve W.......tstat W goes to valve B.
      Then in programming for system type you select #2. (3 wire zone valves-series)
      Then it switches with R as the common from Y to W.
      Just like the mercury bulb with a contact on each.

      Never did one....just now read the book. B)
      ChrisJ
    • ChrisJ
      ChrisJ Member Posts: 16,641
      edited September 2017
      JUGHNE said:

      According to the paper.....tstat R goes to valve R.....tstat Y goes to valve W.......tstat W goes to valve B.
      Then in programming for system type you select #2. (3 wire zone valves-series)
      Then it switches with R as the common from Y to W.
      Just like the mercury bulb with a contact on each.

      Never did one....just now read the book. B)

      If that's the case, and a non-programmable stat is what's wanted.

      http://www.supplyhouse.com/Honeywell-TH5110D1022-The-FocusPRO-Large-Screen-Non-Programmable-Digital-Thermostat-Premier-White-4088000-p


      I assume the 6000's also do it?

      http://www.supplyhouse.com/Honeywell-TH6110D1021-FocusPRO-Programmable-Thermostat-1H-1C-Large-Display-4077000-p

      Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.

    • JUGHNE
      JUGHNE Member Posts: 11,392
      Those papers indicate that series 20 system also.
      But apparently no AC?
      You are using the Y term for the third heat control wire.

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