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Taco Zone control and a T8001 Thermostat compatibility issue.

After searching the forum and not finding a related answer, I have a question concerning a Honeywell T8001 Thermostat and a Taco SR504-EXP-4 Zone controller. The Taco instructions state that for power stealing thermostats, a 1K 1W resistor is placed between the W and C terminals at the controller to supply the T-stat and allow the relay to pick up. I have tried the resistor and cannot get the relay to latch. I tested things with a simple thermostat and the controller works fine that way. Any insight as to why the suggested set-up from TACO is not working correctly?


  • Ironman
    Ironman Member Posts: 6,872
    From what I can see in the manual for the t8001c, it requires the "C" (common) wire to be connected, it's not power stealing. You need to connect the common 24v terminal in the SR504 to the common on the stat.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • pnaffziger
    pnaffziger Member Posts: 2
    That is what I had determined Bob. I incorrectly referred to it a s power stealing like a nest or ecobee although it is not battery powered and does get its power for LCD display and relay operation. I have 3 wire and connected everything per color/letter code but still do not have relay operation at the zone controller. The newer Taco zone controllers also do not have a separated 24V supply but have the C connection fanned out along the terminal board for the t-stat connections. That said, connected according to convention didn't get me there.
  • hot_rod
    hot_rod Member Posts: 16,327

    I thought the resistor is usually to shed excessive current coming back so you don't get a flickering indicator light or chattering relay from the current leaking back?

    It does sound like a crossed wire or open wire. A voltmeter would tell if you have voltage coming back when the stats is on.

    There are some weird PWM stats out there that don't get along well with all relays.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream