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Switching relay

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DaveM
DaveM Member Posts: 51
in THE MAIN WALL
Can I use the taco sr503 exp relay with my L7224 boiler control 

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  • Ctoilman
    Ctoilman Member Posts: 105
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    Yes
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    edited April 2021
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    Isn't this the same discussion you already started?
    https://forum.heatinghelp.com/discussion/184144/line-voltage-thermostats#latest
    steve
  • DaveM
    DaveM Member Posts: 51
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    Yes but you suggested the sr502 the 503 has a C terminal for tstat can I use that relay
  • DaveM
    DaveM Member Posts: 51
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    I have a oil fired boiler with L7224u control there is a tankless coil for dhw and a separate aquaqstat connected to the ZC and ZR terminals on L7224u control. I'm installing a taco 503 switching relay to control the two heating circulators and connecting the ZC and ZR terminals to the L7224 to control priority for the dhw. My question is do I eliminate the separate aquastat that is currently connected to the 7224 control
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,837
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    Is there a wiring diagram on the boiler or in the IO manual so we can see how the aquastat and L7224 is wired? The control logic of the system may need to be redesigned. But the most likely answer is to place all heating zones on a SR50? control (? = 3,4, or 6) and use an end switch to operate the T T terminals on the L7224.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • DaveM
    DaveM Member Posts: 51
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    MR. Ed you helped me back in april just getting back to this project now. I discussed the fact that I have line voltage (120v) thermostats probably from old electric baseboard
    I now have run low voltage wiring to the boiler. you explained the wiring and a diagram which was extremely helpful. I'm confused with the separate aquastat wired to the L7224 Thanks for the help
  • DaveM
    DaveM Member Posts: 51
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    thanks the aquastat is connected to the zc & zr terminals on the l7224
  • HVACNUT
    HVACNUT Member Posts: 5,835
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    What aquastat is connected to ZR,ZC?
    What's it used for?
  • DaveM
    DaveM Member Posts: 51
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    sorry for the confusion just have diagram on the L7224 control
  • DaveM
    DaveM Member Posts: 51
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    that's what I don't understand. The aqua stat on the tankless coil is connected to the zc &zr on the L7224 control. I'm assuming its to provide priority for the dhw. my question is can that be eliminated when I install the taco sr503 and connect that to the zc&zr terminals on the L7224
  • HVACNUT
    HVACNUT Member Posts: 5,835
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    I don't understand the need for a separate aquastat when the L7224U is a triple aquastat itself. 
    What model aquastat is on the coil?
    Its only 2 wires? ZR,ZC to the terminals on the coil aquastat and that's it?
    Can you post some pics. 
    Unless there's something else going on, you could probably eliminate the coil aquastat and use ZR,ZC on the L7224U for the Taco zone panel. 
    STEVEusaPA
  • DaveM
    DaveM Member Posts: 51
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    thanks thats what I'm thinking heading over there now i'll keep you posted
  • DaveM
    DaveM Member Posts: 51
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    turns out the the honeywell control is a L7248 which does not have a ZC terminal therefore it requires a L4006A aquastat on the dwh coil to control low limit What a learning experience. All is up and running fine
  • HVACNUT
    HVACNUT Member Posts: 5,835
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    Ok. Big difference between the 24 and 48. Glad you figured it out. 

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