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Line voltage thermostats

DaveM
DaveM Member Posts: 11
Oil fired boiler with hydronic baseboard elements. Two line thermostats two circulators tankless domestic coil with aquastat  has a L7224 control. My question is how do I convert to low voltage thermostats

Comments

  • Zman
    Zman Member Posts: 6,588
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • DaveM
    DaveM Member Posts: 11
    What is being used as a relay know
  • DaveM
    DaveM Member Posts: 11
    The L2724 is not being used as a relay switch
  • pecmsg
    pecmsg Member Posts: 2,021
    Run Low Voltage wiring. Its not that hard!
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,004
    Why do you need to keep the line voltage thermostats, if that’s really what you have.
    steve
  • DaveM
    DaveM Member Posts: 11
    I’m not keeping old line voltage stats I’m replacing with nest smart stats just trying to understand the old wiring at the boiler
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,004
    Your post was a little misleading. I understood the post as 2 line (line in this context usually means 120 volt) voltage thermostats, which wouldn’t really be possible, instead of 2-wire low voltage thermostats. Coupled with the fact that you said you want to 'convert' them to low voltage.
    Without seeing any pictures, you’re most likely going to have to do what @Zman said
    steve
  • Zman
    Zman Member Posts: 6,588
    I think you will need to give us more info. A quick diagram would help. Do you have 3 wires to the t stats?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,172
    edited April 21
    If I understand your original post, you have 2 zones. Each zone is operated by a 120V circulator that is controlled by a 120V thermostat. The boiler has an L7224 aquastat relay that maintains a minimum boiler temperature for Domestic Hot Water (DHW) The fact that the boiler is always hot means that the heating side of the system just needs to turn on the circ pumps to get the heat into the radiators. Although it works FINE it is not the best setup. (FINE as interpreted the way a wife might say EVERYTHING is just FINE)

    The problem with that setup is you have no "Priority" for DHW. If you are in the shower and there is a call for heat, the cold water from the radiators will enter the boiler. if there is no Low Limit to stop the circulator(s) from depleting all the boiler water, the DHW temperature may drop to low for comfort. (unless you need to take a cold shower because your wife just said Everything is FINE)

    A better way is to use the C1 and C2 terminals on the L7224 control to operate one of the circulator pumps. you do that by connecting the Low Voltage 24V wire to T T on the L7224. This may be a problem with the Nest thermostat, they work better when connected to a common terminal and I don't believe that Honeywell publishes which of the 4 low voltage terminals is Common to the transformer.

    So I will suggest a multi-zone relay to control both circulator pumps and using the ZC terminal to provide DHW priority.
    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,172
    edited April 21
    Here is a diagram you will be able to use. The Switching relay for 2 circulators (Taco SR502 or equal) will provide a way to operate each zone circulator with a Low Voltage thermostat. If your Nest has a problem with insufficient battery charging from a 2 wire setup, then you can try adding a common wire from the thermostat to the switching relay. (see optional green wire on diagram) So run a multi-conductor thermostat wire just in case.

    By using the ZC and ZR you will power the burner to the high limit on the call for heat and restrict circulator operation in the event of insufficient DHW, thus giving priority to the DHW.



    DISREGARD THE THERMOSTAT CONNECTED TO T T ON THE L7224 CONTROL, IT IS NOT NECESSARY

    Respectfully submitted,
    Mr.ED
    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16
    Alan (California Radiant) Forbes
  • DaveM
    DaveM Member Posts: 11
    Ed that was extremely helpful thank you so much 
  • DaveM
    DaveM Member Posts: 11
    Ed is it ok to connect the taco relay to the L1 L2 on the L7224
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,331
    Are you on Long Island? If so, make sure you have 2 individual wires to each thermostat and that they aren't powered elsewhere. Quite a common setup here from the 50's well into the 80's
    To learn more about this professional, click here to visit their ad in Find A Contractor.
    DaveMSTEVEusaPA
  • DaveM
    DaveM Member Posts: 11
    Mr Ed can I use the sr503 with the same wiring diagram you showed me thanks for your help
  • DaveM
    DaveM Member Posts: 11
    Update with a little research found out those tstats were originally for electric baseboard heat
  • DaveM
    DaveM Member Posts: 11
    Some wiring help   I ran the low voltage wiring to sr 503 besides the L7224 on the boiler there’s an aqua stat on the tankless coil do I need to change that wiring 
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