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Honeywell CT87K installation - what am I doing wrong?

I am on my second brand-new out-of-the-box Honeywell heat -only CT87K from a big box store. I cannot make this model work.

I set the two dip switches to "on"; I read and followed the instructions and asked someone else to check what I am doing; I only have two wires, and I have reversed them, as if it would matter; and I have successfully connected and disconnected a more complicated Honeywell type RTH2300B and another digital thermostat multiple times without issue -- I can install and uninstall those other thermostats all day long and have them work without any fiddling.

My only success with the first CT87K I tried, after a lot of fiddling, was that it would be only calling no matter how I set the temperature.


  • IronmanIronman Posts: 4,964Member
    What terminals are you using?
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • SuperTechSuperTech Posts: 938Member
    Do you have it setup for heat pump operation by mistake? If it was configured for heat pump it closes R and Y maybe O as well rather than R and W like a furnace or boiler
  • HVACNUTHVACNUT Posts: 2,031Member
    Your using W and R only right?
    Nothing connected to Y.
    The dip switches are CPH so it should operate anyway.
    Did you try jumping out the thermostat wires?
    Where's the T87F when you need it?
  • 307TurboFire307TurboFire Posts: 11Member
    W and R only. I leave Y alone. Pretty certain it does not have a heat pump setting.

    I can connect and disconnect a RTH2300B and a 2010L, both of which have many more terminals, all day long, so I am not stupid in a general way. Those both operate the boiler as one would expect. I see no need to bypass the CT87K to isolate what is not working, I know there is either a problem with both of the CT87Ks or some subtle problem with the way I am installing them.
  • HVACNUTHVACNUT Posts: 2,031Member
    Nobody is questioning your intelligence. Installing a basic thermostat is not rocket surgery or brain science. Just going through the steps.
    Why are replacing the thermostat? Was there a problem with the original?
    You says theres no reason to bypass the thermostat, but did you try directly shorting the wires?
    Odds are slim that both new thermostats are bad. Possible, but slim.
    If you have an electrical meter you can disconnect the wires from the thermostat and check continuity from the back of the sub base.
  • IronmanIronman Posts: 4,964Member
    Are you trying to install this on a Powerpile system? If so, it won't work. It also won't always cooperate with a zone or pump panel. It's a power stealing thermostat which limits its compatibility with some systems.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • rick in Alaskarick in Alaska Posts: 819Member
    I personally have not had good luck with that thermostat either.I just had one the other day that would not shut off, and it was brand new.
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