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SPDT Thermostats

I know WR still makes the old style stats for the WR zone valves PO/PC. Not to sure about Honeywell though... I to did not know they were phasing out the t-87f stat. Which model did you have?

Mike T.


  • Ken D.
    Ken D. Member Posts: 836
    SPDT Thermostats

    Hello Carol, I just got off a job that was a steam valve actuator, power open and power closed 24VAC (SPDT). The old thermostat was a T-87 that was broken. Went to the supply house and much to my chagrin, the T-87 is no longer available. I knew they were discontinuing them, but I hoped they would still be available for a while. Anyway, my problem was a similar stat was not available to power open and close the valve. The counter guy spent a half an hour looking in his catalogs for a SPDT to no avail. I ended up using a relay to give me the switching I needed. My question is: Does Honeywell make such a stat anymore? If so, what is the designation? Thanks you for your help.
  • Ken D.
    Ken D. Member Posts: 836
    Hi Mike,

    The old stat was an old T-87. Unknown the letter or dash numbers. An electronic T87 is available. One version is digital and the other version has a dial like the old T-87, but the internals are electronic. Unfortunately, neither appears to be SPDT. Thanks for your input.
  • SPDT Honeywell Thermostats

    The old mercury T87s are no longer being made, but I thought that new mercury-free thermistor-based T87s were available now. It's a classic, how could they kill it? The catalog shows T87K as the new mercury-free T87F. It looks and acts like a mercury T87 on the outside, and it wires up just the same, but inside, it's an electronic power-stealer. You'll find cycle rate switches instead of a heat anticipator.

    The magic phrase when dealing with Honeywell is "Series 20," which is what they called their 3-wire power-open/power-closed control system. Their literature may not say SPDT, but if it says Series 20, that's what it is.

    Here are some SPDT options:

    T87K: Electronic mercury-free non-programmable round
    T822G: Mechanical (bi-metal) non-programmable
    TH5000 series: FocusPRO digital non-programmable
    TH6000 series: FocusPRO digital programmable
    TH8000 series: VisionPRO touch-screen programmable

    For the T87K and T822G, you get SPDT switching either R-W or R-Y right out of the box, just like the SPDT mercury T87. For the digital ones, you need to configure the thermostat for 3-wire heat-only operation, otherwise, the Y terminal will be used for cooling.

  • White Rodgers has a SPDT

    thermostat used for their 1311 three wire zone valves. The number is
    1E35-910 Sealed Mecury
    1D35-602 Snap Action

    The old Honeywell numbers were
    T87F-1867 which replaced the old T-26 (Series 20)
  • Glenn Harrison_2
    Glenn Harrison_2 Member Posts: 845

    Personally, I would use the Honeywell Focus-Pro 5000 Series Thermostat. It is configurable for a SPDT operation, such as is used on the White Rodgers Power open/power close zone valves, digital display, which comes in standard and large display versions, battery or 24 volt operation. It is my thermostat of choice for any non-programmable thermostat installation.

  • Ken D.
    Ken D. Member Posts: 836
    Great info

    Thank you all. I knew I could depend on you!
  • carol_3
    carol_3 Member Posts: 397

    Thank you Mark and Glen--you're all over it with correct Honeywell info.

    Ken--please go back and tell your distributor that they need to get up to date. :)
  • Ken D.
    Ken D. Member Posts: 836

    Already done! I have been relentless in busting his chops.Thank you Carol and all.
  • Jed_2
    Jed_2 Member Posts: 781

    I understand the T87K-1007 is SPDT, but, I was told it is "polarity sensitive". Nothing in the instructions mentions this. Why? I've had many come back because Techs are shorting the stat to test, re-connecting to relay: nothing. Send it back, it's no good. They don't know to switch the leads on the relay. Please EXPLAIN! I went through this with a Contractor today on the phone. He had his guy switch leads, and everything was fine. Why doesn't Honeywell TELL people about this?

This discussion has been closed.