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Thread: Right controller???

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    Default Right controller???

    I recently added a second floor addition. For the radiant floor system my plumber installed a Rinnai C85 tank less heater with 3 circulatory pumps. The entire floor is considered one zone even though there are several loop circuits to heat the floor evenly.
    My question is how to hook up the TACO SO 503 controller (that he told me to purchase) to a thermostat that triggers all three pumps to come on at the same time? So far I have only been able to get it to turn one at a time. My plumber is a considerable distance away (for him) and has been less than forthcoming with info or when he's likely to show. I'm trying to get this done so I can move upstairs to so I can finish the downstairs.
    I appreciate any advice and I will check back this evening. Thank you.
    -Michael

  2. #2
    In the Trades Bob NH's Avatar
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    You might be able to hook the one thermostat to each of the three inputs, BUT YOU MUST CHECK OUT THE CIRCUIT TO BE SURE YOU AREN'T CAUSING A PROBLEM.

    By understanding the thermostat circuits I believe it should be possible to connect one thermostat so it causes the controller to actuate all three circulators.

    If you have a meter you can probably check to see if one of the terminals on each of the thermostat inputs is common to all thermostat inputs. If it is, then you can connect THE OTHER thermostat wire to the other not-common returns so it looks to the controller like there is a thermostat on all of them.

    The output relays for the circulators are rated to only 5 Amps so they are probably not large enough to start all of the circulators at the same time.

    IF YOU ARE CONFIDENT WITH ELECTRICAL THINGS you can get a 2-pole relay with at least 5-amp rating, with 120 Volt coil, and connect the coil across the circulator terminals that are actuated by the thermostat. Then supply the poles of the relay with 120 Volts and connect the other two circulators to the outputs of the relay. You will also need to connect the other wire of the added circulators to the neutral.

    If I were doing it myself I would figure out what I had to do to cause the other two output relays to be actuated when the first circulator comes on, without having to add another relay. However, without being able to look at the wiring I have no way to tell you what to do.

    Postscript: I couldn't find the SO503 controller. I found an SR503 controller. http://www.sdsmarket.com/detail.php?id=16328
    Last edited by Bob NH; 03-27-2008 at 02:34 PM.

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    Thank you Bob for answering so quick. There is basically 6 terminals in line for the 3 circuits. One is labeled a "Priority Circuit" and the others zone 2 and 3. I wired a basic thermostat to the priority circuit and wired in parallel (hope that the right term, not "in series" as I try to remember high school electronics class) the other two circuits and lo an' behold it seems to work!
    Now the other question I have is what type of programmable thermostat should I install. I have read somewhere that with the radiant floor system shouldn't have more than 4-6 degrees of separation (Kevin Bacon??!!). I took a tester and there is no voltage across the any of the thermostat terminals if the batteries were to die in any of these new thermostat what does the system do? Do they still use a vial with mercury in it to determine the ambient temperature?
    I bet your sorry now that you volunteered your opinions, but these are the questions that wake me in the middle of the night. Thanks again.
    -Michael

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    DIY Member enosez's Avatar
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    FWIW, The priority zone is usually used for DHW.

    Since all three pumps are coming off one thermostat why waste the money on a 503?

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    In the Trades Bob NH's Avatar
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    Most thermostats operate by closing a contact (a switch or relay) when it calls for heat. The mercury thermostats are just a switch where the mercury-containing part is mounted on a bi-metal coil that tilts it to make contact when the temperature drops. The mercury thermostats have been largely replaced with units that have standard electrical contacts.

    Programmable thermostats contain electronics and usually use thermistors or other temperature sensors together with digital logic. Because most boiler systems rely on contact-closure to turn on the heat, many of the programmable thermostats contain a small mechanical relay to make the closure.

    The boiler control usually provides 24 Volts AC to the thermostat. If a thermostat has batteries it is probably for backing up the memory.

    Some of the new thermostats may require more than a pair of wires. If you get a programmable thermostat you must be sure it will work with your system and you may not want to run new wires through your walls.

    On your 503 thermostat you should turn the priority switch to OFF. Otherwise it will operate only the "Priority" circulator because it will think that is your water heater demanding heat.

    The thermostat doesn't control the temperature difference. That difference is the difference between inlet and outlet temperature of the water in your floor pipes. That is controlled by the circulation and length of the pipes, which is why you have 3 loops in the floor.

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    Quote Originally Posted by enosez View Post
    FWIW, The priority zone is usually used for DHW.

    Since all three pumps are coming off one thermostat why waste the money on a 503?
    I asked myself that same question after I installed it. That's what my plumber recommended to get. Silly me I was the diligent homeowner and did what I was told. I'm testing the system with an old mercury based thermostat. It ran last night set at 65deg. Temp up stairs is at 68 deg. measured with a thermometer at 5' above floor. So far quite pleased with the result.
    I will double check my readings on the controller board maybe my meter was not positioned right because it seems to me there has to be [I]some[I] voltage in order for the thermostat to work. Thanks again for your interest. Ikeep you posted as to anything else I discover.
    -Michael

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