Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.

New Thermostat for 3-wire System

An_Fo
An_Fo Member Posts: 2
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?

Comments

  • JUGHNE
    JUGHNE Member Posts: 8,943
    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: 8,943
    Simplest I know of is HW FocusPRO 5000 series. TH5110D1022.
    Non programmable....might not be in the big box stores.
  • ChrisJ
    ChrisJ Member Posts: 11,974
    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 quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • ratio
    ratio Member Posts: 2,923
    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: 8,943
    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: 11,974
    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 quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • JUGHNE
    JUGHNE Member Posts: 8,943
    Those papers indicate that series 20 system also.
    But apparently no AC?
    You are using the Y term for the third heat control wire.