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Lux-geo thermostat install

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Hi I’m connecting a Lux-geo thermostat to a SR Taco506 with 3 wires. Do I need the “power bridge” they provide and how are they attached in relay switch?  Thanks for your thoughts 

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  • Alan (California Radiant) Forbes
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    See page 3 of the attached Taco application drawings that shows how to connect a Nest thermostat to a Taco SR50X pump control. Your LUX-GEO should connect in the same way. However, from what I understand, there's only enough power for 2 Nest thermostats. Any more and you will need an additional transformer.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Icehouse
    Icehouse Member Posts: 11
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    Thanks will check it out. 
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,004
    edited September 2022
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    Sorry, here's a screen shot:



    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Icehouse
    Icehouse Member Posts: 11
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    Thanks Alan I found the diagram in a previous post and I can do that setup. But the wiring diagram that comes with the Lux shows a setup that is very different, and my issue is that the Taco relay doesn’t have the connection terminals for the 4 wires that the Lux “power bridge” has. I’ll try to post the diagram. Any thoughts? Thanks again for you help.
  • Jamie Hall
    Jamie Hall Member Posts: 23,305
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    As I read the Lux manual, you may not need the power bridge. What wires are present at your old thermostat, and to what are they attached? Assuming you have three wires, one of them -- usually, but by no means always -- is red, and is the hot side of your 24 VAC power. One of them --again usually but not always -- is white, and is the switched wire. And the third, usually green, is the common return for your 24 VAC power.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Icehouse
    Icehouse Member Posts: 11
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    I have the green wire but it’s not used. So if I understand correctly all I need to do is attach the green wire to C at the stat and also to the Taco relay, at the 24v com. 
  • Jamie Hall
    Jamie Hall Member Posts: 23,305
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    Probably. But without being there, meter in hand, I wouldn't want to guarantee it...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Icehouse
    Icehouse Member Posts: 11
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    Along with the red and white 😁
  • Icehouse
    Icehouse Member Posts: 11
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    Thank you guys, Jamie the green wire did the trick no more batteries to worry about the stat is working great😁👍
    Alan (California Radiant) Forbes
  • Icehouse
    Icehouse Member Posts: 11
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    Have to get back to you, the thermostat doesn’t work properly. The Lux-geo is warming up…🤔 don’t know why but the unit is creating a small amount of heat and of course indicating a warmer than actual room temperature so I disconnected the green (common) wire and went back to batteries ☹️
    Back to “square one”, I have the directions provided by Lux-geo but don’t have the necessary terminals on the TacoSR506 to properly attach the “power bridge” shown in the diagram posted earlier. Once again thanks for any input. 
  • Jamie Hall
    Jamie Hall Member Posts: 23,305
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    I doubt very much that the power bridge will help your warming up situation, since all it does -- basically -- is provide a different way for the thermostat to get the necessary power to operate. I would be quite surprised to learn that it fixed the situation, but no harm to trying it -- but don't be disappointed if it doesn't work.

    That said, is the thermostat mounted so that air can circulate freely around it? Being a wi-fi thermostat, it actually uses a surprising amount of power -- which appears as heat which in turn has to go somewhere. The parts of its operation which operate only on batteries don't generate much heat -- it's the wi-fi transmitter and associated circuitry.

    It really shouldn't be a problem -- other wi-fi thermostats don't seem to be affected by that (they have other problems -- but not that one!). Does the temperature stabilize at some given value over ambient, and -- importantly -- ambient measured exactly at the thermostat with a reliable thermometer?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • HVACNUT
    HVACNUT Member Posts: 5,841
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    What kind of heat do you have? Baseboard or radiators, or a hydro coil with a fan? No air conditioning? 
    Any zone valves?
    If the wires go straight from the SR506 to the thermostat then there shouldn't be a problem. If only Red and White were being used, maybe there's a splice somewhere and Green wasn't spliced through. 
  • Icehouse
    Icehouse Member Posts: 11
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    We have a Navien on demand propane baseboard heat system that serves 5 zones with a Taco SR506 relay but only one zone is connected with the Lux-GEO thermostat. I have 3 wires using just the red and white wires with batteries powering the stat. My problem is I would like to power the Lux-GEO without batteries through the Taco. Tried connecting the green wire to the C terminal on the stat and the com terminal on the Taco, and the stat warmed up about 4 degrees above room temp. So I’m back to the batteries. 
  • HVACNUT
    HVACNUT Member Posts: 5,841
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    Icehouse said:
    We have a Navien on demand propane baseboard heat system that serves 5 zones with a Taco SR506 relay but only one zone is connected with the Lux-GEO thermostat. I have 3 wires using just the red and white wires with batteries powering the stat. My problem is I would like to power the Lux-GEO without batteries through the Taco. Tried connecting the green wire to the C terminal on the stat and the com terminal on the Taco, and the stat warmed up about 4 degrees above room temp. So I’m back to the batteries. 
    Are the terminals in the relay marked T-T or R-W?
    You could try switching Red and White. No reason it shouldn't work unless there's a problem with the thermostat.