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tech tip for honeywell 8124 and taco sr504

jon_6 Member Posts: 26
and came across a touchy situation. was replacing 2 old relays with a taco sr504 ( to used with tankless coil) the relays had their own power source and so did the burner which is an interburner. Wanted to use zc and zr to kick out the circulators. wired all up to instructions and all was fine untill the temp of the water went below the low limit set point wich was 170 deg. at this time the burner circit breaker had tripped, resulting in a loss of power to the burner side of the breaker. The taco circulator zones where kicked off. at this point the burner was still running out of control neither the low limit or high limit was shutting down the burner. what was happening was the taco was back feeding into the 8124 threw the zc/zr teminals. finally tested electrical flow with digital meter and found out. The tip is to have only one power source when using taco controls and zr/zc terminals.


  • Very good advice

    We run into this situation sometimes , where someone picked up power to a relay from another source , not the boiler curcuit . I wonder if its a code to have all the heating appliances on one dedicated circuit breaker ? Thanks for the heads up Jonathan .
  • Dave Flood
    Dave Flood Member Posts: 14

    Hi Fella's,
    The 1996 International Mechanical Code book states that a heating system will be on a deticated circuit breaker. I'm not familiar with the taco zone control you soek of, but I will get one and check out the wiring. If its anything like the wiring of a system with a Honeywell 8124, connected to the Honewell 845's for additional zone's, be careful with the wiring. Many techs wire the zc and zr terminals wrong. When we do, we draw to much current through the 8124 eventually burning out the control. It sounds like possibly this may be where yor proble is, but without seeing the schematic, I'm not sure. The Honeywell 8124 zc terminal should only power up terminal number 1 of the 845. By doing so we only suppy power to the transformer of the 845.

    Dave Flood
    Dir of Tech Ed
    ICPA Tech Trng Ctr
    Wallingford, Ct
  • jon_6
    jon_6 Member Posts: 26
    tech tip

    after i removed the second power source to the taco sr504 we tested the zc/zr terminals on the honeywell 8124 and found out wich one controlled the relays from kicking out. i think the zc had power to the zc on the taco, which kept the the circulators on and the zr was not energized. they say in the instructions to maintain polarity between both lines. thank. all the signals are off of the 8124 circuit i got very lucky that the circuit breakers had tripped or it would have been a long night.i hooked the taco on the same circuit as the burner and it works just like it was intended to.
  • Alan R. Mercurio
    Alan R. Mercurio Member Posts: 588
    Here's how I wire them.

    Jonathan, Thanks for the tip. for what it's worth I thought I would share how I wire them.

    Let’s start with the R845A the terminals and their purpose. We have L1, L2, T T, 3,4,5 and 6.

    Now L1 (hot) simply provides power to the transformer in the R845A.

    L2 serves as our neutral for the transformer in the R845A and the circulator we will be wiring into the R845A.

    The T T terminals are for the thermostat in the corresponding Zone.

    Terminal 3 provides power to terminal 4.

    Terminal 5 provides power to terminal 6.

    With me so far? Good let’s keep going.

    Now we are going to look at that the Aquastat. To keep this simple (and that’s how I like it) We will just look at the terminals we need to run to and from the R845A.

    L1 (hot) Terminal ) The line voltage at the aquastat. This will provide power to Terminals 3 and 5 in the R845A switching relay.

    L2 (white) Terminal ) The neutral line at the aquastat. This will provide a neutral source to the L2 terminal of the R845A switching relay.

    ZC Terminal (Zone Control) this provides power from the aquastats low limit side to the L1 terminal of the R845A switching relay.

    ZR Terminal (Zone Return) This receives power from terminal 4 of the R845A switching relay.

    Are you starting to see how easy this can be? Now if you’ll allow me to ramble on a bit here I’ll explain what goes on with these controls. You notice we supply power to the R845A VIA the ZC terminal of the aquastat. Why? Because we do not want the additional zone to operate unless the boiler is at or above the desired low limit setting! This is no different then what takes place with the aquastat operating a single zone from terminals C1 and C2. If we allowed it run below the low limit we would just be circulating cold water this will cause the boiler to run a lot longer then necessary, possibly never catching up with the demand. Thus leaving our customer uncomfortable and costing them more energy dollars then necessary.

    The ZR terminal. Now here’s one that had me confused for years (not a hard thing to do). Remember this terminal receives power from the R845A. In my mind what’s happening here is this, When there is a call for heat and the relay in the R845A is closed we now have power from terminal 4 in the R845A going to ZR in the aquastat. You see this is how the R845A communicates with the Aquastat! You’ll notice ZR is tied into the Blue wire leading to the high limit side of the aquastat. When ZR is powered it is letting the burner know there is a need for it to come on and maintain our water temperature. If the High limit is met then the burner will not come on and this will prevent it from overheating the water in the boiler. You see, again this is no different then operating an aquastat without an additional zone.

    Is this starting to make sense now? Of course it is!

    Terminals 3 and 5 always have power ready to go to work for you. What’s up with that?

    Here’s the deal, in the R845A switching relay terminals 3 and 5 are on the Normally Open (NO -/ /-) side of the control. When there is a call for heat the 24volt relay pulls the contactor in the R845A closed, and the circuit between terminals 3 & 4 and terminals 5 & 6 now become Normally Closed (NC -//-). The power from terminal 4 goes to the ZR terminal we just talked about above and the power from terminal 6 goes to the line voltage L1 side of the circulator for that zone. Keep in mind the power supplied to terminals 3 and 5 do not have to be from the aquastat. If it is more convenient you can run power from your main fuse panel to these terminals.

    Note: When wiring an R845A that is operating with a programmable thermostat it is recommended the thermostat have, a battery back up. Remember when ZC is not energizing the L1 terminal of the R845A the programmable thermostat will not have power and may lose its memory! Boy I wish I could add a battery back up for my memory.

    Now you see how easy it really is? Here is my secret to never forgetting this and a lot of other technical information I have obtained over the years, I could never keep all the information that we must know and learn neither could or would Albert Einstein! So I take anything I learn and write it down. I collect all the technical information I can get my hands on. and I keep all this in a file I like to call my ‘Tech Tips’. You see it’s not about knowing everything there is to know. It’s knowing, where to find the information when you need it and understanding how to apply it! So I respectfully suggest you start your own tech file if you haven’t already? And if you find the information above useful I welcome you to add it to your files and share it with as many people as you like. Remember the knowledge we share today, will build a better industry tomorrow.

    Your friend in the industry,
    Alan R. Mercurio

    Industry Consultant

    Oil Tech Talk

    [email protected]
  • Have a wiring diagram available for

    this situation if you are interested.
  • Or you could attend

    Alans or my training classes on hydronic controls. There is more to this hydronic business than the piping and plumbing and water flow. Everyone needs to understand the controls that make it happen.
  • Alan R. Mercurio
    Alan R. Mercurio Member Posts: 588
    If a choice needed to be made

    I would go to Tim's class. I hear he knows some things about this business :)

    Of course I would always be happy to see any of you.

    Thanks for all you do Tim.

    Your friend in the industry,

    Alan R. Mercurio
  • mell
    mell Member Posts: 2

    during hurricane sandy i wired an extension cord to the line side of my taco sr504 without considering polarity . my boiler fired up and the circulator allowed   it to make hot water. i repeated this many times over 5 days using an unpolarized cord. it worked every time.does it matter how it is wired?
  • mell
    mell Member Posts: 2

    during hurricane sandy i wired an extension cord to the line side of my taco sr504 without considering polarity . my boiler fired up and the circulator allowed   it to make hot water. i repeated this many times over 5 days using an unpolarized cord. it worked every time.does it matter how it is wired?
  • SWEI
    SWEI Member Posts: 7,356
    should work either way

    As long as nothing bad happens.  The risk from incorrect polarity is either shock (from a lifted wire) or fire (from a grounded wire.)
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