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Thread: How do I wire a SR503 to a L4081B Aquastat?

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    DIY Junior Member paulfromny's Avatar
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    Default How do I wire a SR503 to a L4081B Aquastat?

    Hello. Im in the process of replacing my 57 year old oil boiler. I just purchased a used Weil Mclain Gold WTGO-3 Boiler with a Riello 40 burner for $500. The old boiler is on its way out and I need to replace this thing before the winter. The used WM is about 6 years old and in excellent shape. The original owner switched to gas. It came with two 007 Taco Circulators installed on the feed, a L4081B Aquastat, a DHW coil, and a safeguard 170SV low water cut-off installed on the feed.

    I asked the origianl owner if he was running relays for low voltage thermorstats or just direct line voltage, but he didnt know, as he was not to familiar with burners at all. All the wires, including the circulators, come to a junction box with a service switch. All the neutrals come together in this box. There are 4 wires coming out of the junction box. 2 Line wires,( 1 each for the circulators) 1 Line wire for the service switch, (which leads to the water cut off H terminal), and 1 red wire, ( which leads to the W terminal (LOW SIDE) of the aquastat).

    The other wires going through the junction box are as follows. 1 Black wire coming from the burner going to the B terminal (HIGH SIDE) of the aquastat. 1 green ground wire coming from the burner, grounded at the junction box. Last, 1 red wire coming from the water cutoff (terminal P2), going to the R terminal at the aquastat. Again, all the neutrals are tied together in the junction box.

    If im not mistken, its kind of simple how its wired. Line voltage is intorduced to the service switch, in turn, going to the low water cut-off. As long as theres water in the feed, the low water cut-off supplys power to the P2 terminal going to the R terminal (HIGHT SIDE) at the aquastat. (low water-cutoff acting like a simple switch). From there, the aquastat has 120v introduced, firing the B terminal (HIGH SIDE), A nomaly closed switch, in turn firing the burner, up until its set temp (180F +/- Diff), then the switch opens, shutting the burner.

    On the low side of the aquastat has got me stumped. Again I have a red wire coming from the W terminal from the aquastat, coming out of the junction box. Not sure where this went. The aquastat has 2 terminals up top. 1 B (spade Terminal) on the HIGH SIDE. 1 W (push in terminal) on the LOW SIDE. On the bottom of the aquastat there are 2 R terminals. 1 on the HIGH side and 1 on the LOW side. They also have a jumper installed, jumping the two R terminals.

    Im adding an additional zone to the unit (total of 3) with low voltage thermostats. I know to move all the ciruclator wires to the SR-503 Box, and to bring in Line Voltage to the SR-503 from the low water cut-off/service switch) to power the board. My question is how do I wire a Taco SR503 to this aquastat?

    The aquastat has NO T-T or ZR ZC connections. Im guessing it gets wired to the low side of the aquastat, but do I remove the jumper at the R-R terminals? Im not too sure which is which on the SR-503. Does the ZR send 120V or senses 120v on the SR-503? or vice versa with ZC? Do I keep the burner black wire on the B terminal and the 120v red wire (from the water cut-off) on the R terminal (HIGH SIDE). Also, the burner will provide DHW with the built in coil, so it will need to fire for how water, even when theres no call from a thermostat. If I wire the SR-503, will it still fire at the LOW setting (160F +/- DIFF) if the jumper has to be removed at the R-R terminals?

    I searched all over the internet for an answer and also contacted TACO. The answer I received from taco is to connect the SR-503 to the thermostat I was using originaly. That didn't really help. Im still stumped. The rest of the install is very simple for me, but this has got me stumped and I just dont want to cross wire anything. A simple solution would be to change the aquastat, but If i dont have to right now, I rather not. Thank you all for any solution.

  2. #2
    In the Trades Tom Sawyer's Avatar
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    All of the line voltage controls are essentially switches. Power runs through the service switches and then though the low water cutoff, the high limit aquastat and the low limit aquastat and finally, down to the oil burner primary control. A leg of the high voltage also feeds the SR relay panel as well as the low limit side of the aquastat. All of your low voltage thermostats get wired to the TT terminals on the SR relay. All of the circulators get wired to the circulator terminals on the SR relay ( right below the TT terminals to keep wiring straight ) The TT terminals on the SR relay get wired to TT on the oil burner primary control. You can find all of the diagrams here.

    www.taco-hvac.com
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    DIY Junior Member paulfromny's Avatar
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    Thanks for the response. There is no T-T terminals at the burner primary control. Its a Riello 40 burner. I understand how to wire the circualtors and thermostats at the SR-503, but how do I tie the SR503 to the boiler with no T-T or ZC ZR connections on my aquastat. The following picture shows a wiring diagram of a circulator being used with this aquastat, and the SR503 should be used with the ZR ZC connection if used with a tankless DHW heater, as shown in the wiring diagram below. Again my burner is NOT a cold start unit as it provides domestic hot water.


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    Taco has a frequently asked question section and found this explanation of the ZC ZR connections, but im still a little confused. Does the SR503 Board need to be tied to the aquastat at all, or can it be used as a stand alone unit. If I need to wire the SR-503 to the Aquastat. Which wire goes where? Can someone please help. Thank You so much!!!!


    (FROM TACO's WEBSITE, THIS MAY HELP YOU TO HELP ME UNDERSTAND ... PLEASE)


    Q. What are the ZC and ZR terminals on the SR506 and how are they used?

    ZC/ZR terminals on the SR board go to ZC/ZR terminals on the triple aquastat with ZC/ZR terminals, using minimum 14 gauge wires. These terminals will prioritize domestic water coil. When there is a demand for heat from the thermostat, ZR becomes hot, sending 120 volts to the triple aquastat. When the boiler temperature rises above the minimum temperature setting (typically 140), ZC becomes hot, sending 120 volts to the SR board and powering the relay for the circulators. To recap, the circulators cannot run until the boiler is keeping up with demand.


    Q. I need technical details on how the ZR and ZC terminals interface with the aquastat on a boiler. I wire many boilers and all directions specify cold start or hot start, black box type instructions. I do not fully understand the inner workings, or what happens electrically with either application.

    In our Control Instructions, we give two examples: a cold start boiler or a tankless coil boiler. For the cold start, the X, X goes to the TT terminals in the boiler control. For the tankless, the ZC and ZR go to the ZC, ZR terminals of the boiler. Boiler controls that don't have ZC and ZR terminals can be hooked like the cold start. These hook ups are conditional, in that you move the circulator that was originally wired to C1 and C2 over to the Taco Control.
    If you plan to leave the circulator on the boiler aquastat, and a thermostat connected to the TT terminals of the aquastat, you will need to get into the firing circuit of the aquastat. This would be the ZR connection. Run a wire from the ZR of the aquastat to the ZR of the Taco control. If there is no ZR, run a black wire from the ZR of the Taco control to the B terminal of the aquastat.
    When an aquastat has the ZC and ZR terminals, the ZC is connected to the low temperature switch of the aquastat and to the ZC terminal of the Taco control. The ZR is connected to the ZR. These will be 120 Volt wiring. When the boiler water temp is too low, the low limit switch connected to ZC opens and drops the voltage to the ZC of the Taco board, killing all the pumps until the boiler catches up. The ZR is a 120 Volt supply to the burner circuit to fire the boiler, but this goes through the high limit switch to control the boiler water temperature.

  4. #4
    In the Trades Tom Sawyer's Avatar
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    You will need another relay such as a honeywel RA845 or 89a TT from the relay to X1 + X2 on the SR and then line voltage to the riello's primary
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    DIY Junior Member paulfromny's Avatar
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    OK, but how would I wire the RA89A relay to the aquastat?

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