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Old SR503 wiring for a new thermostat

Ed Lentz_2
Ed Lentz_2 Member Posts: 151
Hi ,
I have an old SR503 that has worked well for about 15 years. Now coming into the 21st century I want to connect a Centralite Pearl thermostat to it. The thermostat needs 24v, C and a W to go to the SR. Can a powered thermostat be wired to the SR? I see a 24v connector on it that is unused. How is the T input on the SR503 arranged?
Thanks for any help

Comments

  • Steamhead
    Steamhead Member Posts: 15,756
    edited July 2022
    Not sure if the transformer in the SR503 is big enough to handle this. If it is, use your voltmeter to check for power between R on the thermostat block for the zone you're using, and the 24V Common terminal on the board. If you get this voltage, the C wire from the thermostat would then go to Common.

    But you need to call Taco tech support to see if the transformer is big enough. I saw no mention of that in the online manual.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
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  • Ed Lentz_2
    Ed Lentz_2 Member Posts: 151
    Thanks for the reply Steamhead,

    The terminals on the SR503 are labeled T T. Should i assume that the one I get NO voltage between C and one of the terminals that it is the one that I hook to W1 on the thermostat?
  • SteveSan
    SteveSan Member Posts: 156
    @Ed Lentz_2 Does your SR control have a metal cover? If so, when you need to connect a com you need to make sure your t-stats wires are connected this way. Red to the left T and white to the right T. Then connect your com to the com side of the 24vac/com terminal. Any questions you can always call us here at Taco Tech Support 401-942-8000 Mon-Fri 8am-5pm EST
    EdTheHeaterMan
  • Ed Lentz_2
    Ed Lentz_2 Member Posts: 151
    SteveSan,

    Thanks for the Info and the phone call!! I will let you know how it works out.

    Ed
    SteveSan
  • HomerJSmith
    HomerJSmith Member Posts: 1,923
    The Taco SR has a 24 VAC-15VA (volt amp) transformer. That is a three zone relay for three pumps. So, you have three zones with three thermostats and you want to replace one thermo with the Centralite Pearl thermostat?

    I am wondering about the current draw for the 15VA (volt amp) transformer.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,946

    The Taco SR has a 24 VAC-15VA (volt amp) transformer. That is a three zone relay for three pumps. So, you have three zones with three thermostats and you want to replace one thermo with the Centralite Pearl thermostat?

    I am wondering about the current draw for the 15VA (volt amp) transformer.


    @Ed Lentz_2 can always replace the transformer in the Taco SR with a 30 VA or 40 VA transformer if needed. (the "if needed" will be when the 15 VA transformer fails, or the fuse fails if it is equipped with one). other than that, if the transformer lasts another 15 years, then Ed is good to go. The TACO guy (Steve) said so above when he gave the wiring instructions.

    Edward Young Retired HVAC Contractor & HYDRONICIAN Services first oil burner at age 16 P/T trainer for EH-CC.org
  • HomerJSmith
    HomerJSmith Member Posts: 1,923
    edited July 2022
    I have replaced the 15 VA transformer with a 30 VA transformer in failed SR's. I found that is the largest VA you can go and get the cover on the box.

    The older metal covered SR's have the transformer bolted on the circuit board. Changing over the transformer requires some skill.
  • Ed Lentz_2
    Ed Lentz_2 Member Posts: 151

    I have replaced the 15 VA transformer with a 30 VA transformer in failed SR's. I found that is the largest VA you can go and get the cover on the box.

    The older metal covered SR's have the transformer bolted on the circuit board. Changing over the transformer requires some skill.

    I actually thought about doing that if needed. In another life I troubleshot, rapaired at the component level on many different circuit boards. This would be a piece of cake.

    The other two zones are controlled by relay contacts, another of these might be installed so only two that I can see for now at most.

    Other than the thing is set for C instead of F it is working from the unit itself and the hub it is connected to can control it remotely, so it is working the way I had hoped it would.

    Thanks everyone for the suggestions, much appreciated
    SteveSanEdTheHeaterMan