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Zone/circulator runs continuously. Thermostat not bad. Turns off when thermostat unplugged.

mabo
mabo Member Posts: 20
in Thermostats and Controls
Hi All, I have a heating zone that is powered by a dedicated circulator and whenever the thermostat is plugged into its socket, its circulator runs continuously. Doesn't matter what setting on the thermostat, off/heat/cool, etc. I tried another thermostat of the same type that is in a different room and that I am pretty sure works properly, and I get the same results. To turn off this zone I would just have to unplug the thermostat and it turns off.

This zone is a backup zone and I never ran it until now, so I can't be sure whether this has worked correctly in recent times. At the Taco zone board, that zone looks to be wired identical to all the other working zones. Here is what the wiring behind the thermostat looks like:



Any ideas what might be happening or how to diagnose further?

Comments

  • HomerJSmith
    HomerJSmith Member Posts: 2,628
    I was thinking there was a short in the thermostat wire, but if you pull the thermostat out of the circuit and the circulator turns off then that wouldn't be the case.

    There is a relay in that zone. You mentioned a Taco board what is the product #? You have other zones that run off that Taco board and they are circulators, too?

    Taco boards have a priority zone in them which is usually connected to a domestic H/W tank which when in the priority mode turns off all the other zones and directs the heat to the tank. It is possible that the circulator is on the priority zone. There is a small switch the you can shift from priority to normal operation. Maybe that circulator is connected to the priority zone and in the priority mode. If so move the switch to normal operation. I think that I remembered this right.
  • HomerJSmith
    HomerJSmith Member Posts: 2,628
    Some Taco circulators have a built-in (dedicated) relay and thermostat connectons. Is that your case?
  • Zman
    Zman Member Posts: 7,611
    A picture of whatever is on the end of those wires would help.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    What's this 'plug' and 'socket' you speak of for the thermostat?
    If you mean when the thermostat is plugged into the base, it runs no matter what, then change the batteries, check the pins.
    Maybe you are pinching a wire when you reattach it to the base. Can you push the slack back into the wall.
    Could still be a short and taking the base off is moving the wires enough. Try pushing moving the wires and see if you hear the circ.
    If none of that works, I would just replace the stat, after ohming out the thermostat wires for continuity.

    There was an error rendering this rich post.

  • HomerJSmith
    HomerJSmith Member Posts: 2,628
    You can try removing the RC to R jumper and see if that makes a difference.
  • mabo
    mabo Member Posts: 20
    On the other side of this thermostat the wire connects to a zone Taco SR-506 board, which then triggers a circulator. Somewhere in the middle of this wire, I suspect there is some "other legacy stuff" going on because there is an unexplainable zone valve that is manually opened and doesn't seem to serve a purpose anymore. This is what initially made me think that perhaps the wires are bad.

    But then I started to think about this some more. If I the red and white wire from the zone bard in the wall get crossed, that just should turn on the circulator? In essence the thermostat when it calls for heat basically does this?

    With that being the case, I didn't see how anything but the thermostat would be to blame. I went back and plugged in the other "known working" thermostat, and somehow this time it seemed to behave as expected. I just don't know how I did the test initially that it didn't work. I did push the wires back into the wall as well.

    For sake of intellectual curiosity, how can I prove to myself that the thermostat is actually bad?
  • Zman
    Zman Member Posts: 7,611
    If you use a multimeter to check continuity, the R-W should show open when there is no call.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • ratio
    ratio Member Posts: 3,777
    If you pull the wires off at both ends you can use a multimeter to check for shorts, although a megger is better (but not as cheap!).
  • mabo
    mabo Member Posts: 20
    Ratio, Do you mean to pull wires for this zone at zone board and then test for continuity? If there is continuity then there is a short, otherwise ok?
  • ratio
    ratio Member Posts: 3,777
    Off at the zone board & off at the stat, pull them out so they're just sticking up in the air, not touching anything. You'll read continuity through the zone panel and stat. Once they're isolated, with the meter set to continuity or a low ohms (Ω) range, go between every wire. You should show open (no continuity/beep; or infinite resistance). After that, check for shorts to ground the same way. That'll probably be easier at the boiler, find a clean spot of metal somewhere on/around the boiler as it should all be grounded.

    This process will locate most shorts. Occasionally there'll be a near-short or a weak spot ion the insulation that a multimeter won't find, that's where the megger shines. It uses a high voltage (50-1000 volts with the Fluke I linked to) to test with, as opposed to the <1.5V that most multimeters use, which will push through any marginal spots.

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