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Strange (but probably okay) wiring between aquastat and burner control

netw3rkernetw3rker Member Posts: 3

I'm in the process of getting an inventory of all of my burner components for a much larger project I plan on undertaking. So step one is to figure out what components have what wires, and figure out where they go. In doing so, I noticed an odd configuration where I have an on/off switch labeled "boiler service" and it has 3 lines coming out of it. One is clearly the power in, then one goes to the Carlin 60200-02 boiler control, and the other to the Honewell L8124A,C Aquastat.

I thought that was odd since the Aquastat is supposed to power (or at least signal) the Boiler Control through the B1 & B2 connections, but there's no clear connection between the two devices, just this on-off switch. I opened the switch/box to take a look, and what appears to have been wired is the Red for the L1 of the Aquastat, and the Red for the Boiler Control have been spliced together at one end of the switch, and the other end has the red from power in (I get that that's clearly to shut power to the boiler off if need be). then the white wires for L2 on the Aquastat, the white wire to the Boiler Control, and the other Power in are all spliced together. Finally, the black wire runs from the Aquastat's B1 position to the Boiler Control.

I read through the schematics and installation manual for the Acquastat and I cannot find any reference to this kind of configuration, which makes me even more curious what's going on, but from the schematics it appears that those are roughly equivalent, and it of course seems to be working fine. So my real question is: Why would the original installer wire it this way instead of connecting (BC)Red to (Aquastat)B1, and (BC)White to (Acquastat)B2?



  • STEVEusaPASTEVEusaPA Member Posts: 4,308
    edited December 2019
    That primary requires constant power for post purge, and onboard diagnostics. Usually power passes thru the aquastat to the primary control on L1, B1 on aquastat goes to limit on primary control.
    What’s the other project you are undertaking?
  • netw3rkernetw3rker Member Posts: 3
    Gotcha, so B1 & B2 on the Aquastat are used when the primary doesn't require constant power? Interesting. Out of curiosity, if that's the case and according to the diagram on page 7 here: aren't B2 and L2 effectively the same? so really just wiring L1 direct to the main would be enough right? Or is it just this way because its clearer to electricians what's happening when L1 & L2 are run together?

    The larger project is adding in a Taco Zone Control system. We have 4 zones and a single circulator (though there is one on the small water tank), but are constantly losing hot water when all zones are active (and it's not even cold outside yet). I'm pretty sure this is largely because of the lack of dedicated switching when hot water is requested (My understanding is, this is native functionality in Tacos)

    On top of that, we got a great deal on 4 Ecobees. Our in-wall wiring has 3 wires, but the Aquastat only provides contacts for 2 of them - so they don't work yet, but at least the in-wall can handle it once it's available. An added benefit to installing the Taco is that each of their Thermostat zones offers the necessary C wire contact, So I'd be killing two birds with one stone.

    My plan is to drop the Aquastat's thermostat and circulator handling, and move the valve, thermostat, and circulator pump handling to a Taco (haven't decided on a model, but I might go with the 6 zone, 2circ option so I have room for expansion)

    I'm assuming that this Aquastat doesn't actually care about the Thermostats and can work as a standalone boiler water temperature monitor that will active the BC when the temperature drops, regardless of what the zone thermostats say right?

    PS: Nearly every HVAC person has looked at me crosseyed about this, mainly because the wiring on the boiler is such a disaster, but I also suspect it requires a special kind of electrician for this, and they haven't been that. But also, the time, equipment and rewiring costs for them to do it really don't justify this "just for ecobees". So I'm content to just do the bulk of the work myself if it's possible.
  • STEVEusaPASTEVEusaPA Member Posts: 4,308
    You should look at the wiring schematic for the primary control. Your aquastat is older generation and the wiring schematic probably predates modern primary controls.
    Yes B2 and L2 are the same, but I think you have a typo (or I don't understand the comment "...when L1 & L2 are run together. Connected together would not be correct as you would have a direct short. But generally people like to see hot's and neutrals running in the same direction. One way, from the aquastat should be a 3 wire to the primary, with B1 (black or red, I like red) going to 'Limit' on primary, Black on 3 wire either coming from L1 on aquastat or better, wire nutted to L1 on aquastat and going to L1 on primary, and white hitting B2 or wire nutted to L2 on aquastat, and L2 on primary.

    Without re-piping (or seeing a schematic) the Taco Zone control will have a priority setting for the indirect zone.

    Yes. Any zone calling will close the X-X terminal on the zone control and complete the T-T circuit on the aquastat to fire the burner if you are not at/above the high limit setting.
    Honestly if you're going to redo all of this, get a modern aquastat like the 3250+. More features, and change the well and get LWCO.

    As far as wiring, just get a competent oil company tech to come over and wire it. Electricians may not be good/familiar with controls. And people who only do gas, aren't always familiar with the concept of oil and line voltage controls.
  • netw3rkernetw3rker Member Posts: 3
    " But generally people like to see hot's and neutrals running in the same direction."

    That's a correct rephrasing of what I was saying about L1 & L2.

    As a layperson, I envision the BC as a component that connects to the Aquastat, so I would expect Hot, Neutral, and Limit to come from the Aquastat. For me, it's weird to see Hot and Neutral come direct from the main, and Limit come from the Aquastat but I can see why to a pro it would make more sense this way.

    Looking at the 3250+ it looks like a pretty straight forward wiring swap based on this:
    I think I'll run into the same "no C wire problem" though; unless there's an undocumented connection spot in the pdf in the link above right?

    If I keep the current Aquastat and add the Taco, I'd assume I'll have to have it signal the acquastat via the TT lines so that it can kick everything into gear right?
  • EdTheHeaterManEdTheHeaterMan Member Posts: 719
    Some assumptions are made that may not be accurate. L8124a is for a tankless coil water heater. @STEVEusaPA mentioned an indirect water heater having priority. @netw3rker mentioned insufficient DHW when a zone calls for heat *** this is another clue for tankless coil DHW. There may be some circulators operating without the benefit of ZC from the L8124 to maintain minimum boiler temp.

    Hay!@netw3rker... Where are you getting hot water from?
  • EdTheHeaterManEdTheHeaterMan Member Posts: 719
    edited December 2019
    If the zoning is being done with circulators use this diagram to give the tankless coil DHW priority
    The ZC and ZR are both connected to the Taco and the Honeywell. This makes all the circulators on the Taco zone control operate the same as the circulator on the Honeywell L8124. This means if the boiler temperature drops below the minimum to maintain DHW all circulators will STOP and wait until the boiler temp rises to a differential setpoint when the circulators can come back on.

  • EdTheHeaterManEdTheHeaterMan Member Posts: 719
    edited December 2019
    @netw3rker said: If I keep the current Aquastat and add the Taco, I'd assume I'll have to have it signal the aquastat via the TT lines so that it can kick everything into gear right?
    The answer is YES, if you are using zone valves and a zone valve control.
    NO if you are using Circulators for zoning. See above
    Need to know about your hot water. Where does it come from?
  • STEVEusaPASTEVEusaPA Member Posts: 4,308
    “...We have 4 zones and a single circulator (though there is one on the small water tank)...”

    I took that as an indirect with its own circulator.
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