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Taco SR504-EXP-4 to Honeywell L8184 Aquastat Help!

I am looking to upgrade 3 Honeywell RA832a relays that control the hydronic circulator pumps on my boiler.
Pic 1.= Honeywell relays

The problem with the current setup is the need for a common wire to power my smart thermostats. The current setup is power robbing from one another and so I purchased a Taco SR504-EXP-4 which has a three wire setup for a common wire.
I have a Burnham Low pressure Gas Boiler with a honeywell L8141e aqua stat that calls for the temp to always be 200 degrees.
The current setup has 2 thermostats(zones) with an indirect domestic hot water heater with aqua stat for a total of 3 zones.

I am also confused about this 24v relay that is wired with 24v wiring from the 3 Honeywell RA832a and also the hot water heater aqua stat and then into the "TT" inside boiler aqua stat.
My guess is this relay sets priority to DHW circulator.
Pic 2= 24v wiring relay from the 3 Ra832a's

Does the Taco Board replace this relay?

The boiler has L1 and L2 wires that are currently run to one of the Honeywell relays
and the "TT" is wired from the 24v relay.

How are L1 and L2 wired if the 120 volts is being used by the new taco switch?
What output on SR504 provides the aqua stat with 120v?

I do not see Zc and Zr on this aqua stat. (Honeywell L8184)
The Taco board does not discuss anything regarding L1 an L2 also...
Pic 3= Taco SR504 Board

Pic 4= Honeywell Aqua stat

Can anyone help?


  • Zman
    Zman Member Posts: 7,606
    The thermostats are self explanatory. The aquastat on the indirect is just a thermostat, wire it the same way.
    L1 and L2 are just power to the boiler. Its sounds like they connected it though one of your relays. You just need to provide power to the boiler.
    I agree that the relay is probably for DHW priority. You won't need it anymore, just wire TT on the Taco to TT on the boiler and set DHW priority on the Taco (the dhw needs to be connected to zone 4).
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • DoubleD629
    DoubleD629 Member Posts: 3
    edited February 2020
    Yes, L1 and L2 are definitely wired through one of the relays.
    Should I split off of the current 120v junction box power to get another source of 120v?
    One for the Input to Taco Relay and another for the boilers aqua stat on L1 and L2?
    The 120 needs to come from the same box that has the emergency shut off, correct?

    HVACNUT Member Posts: 5,888
    The relay, as well as anything else for the boiler must be all on one dedicated circuit.
    Just wire the zone board direct, after the emergency switch.

    I agree that GP relay is for DHW priority and is no longer needed.

    Like @Zman wrote, power the zone board, wire the thermostats to their corresponding circulators using zone 4 for DHW priority if needed.
    The connection between the zone board and the aquastat will be 24v thermostat wire from X X on the zone board to TV-T on the aquastat.
  • Joe Mattiello
    Joe Mattiello Member Posts: 707
    Did you add an indirect heater too?
    I’m sorry if I missed that. If you did add indirect, you should use zone four for DHW. And XX in st504 to boiler Tt terminals using low voltage to fire the boiler that can be used as cold start as opposed to tankless maintaining what you Qualified as 200 degrees maintained. Lots of wasted energy
    If you’re still using tankless, you can lower boiler min temperature ti140 degrees to save some energy, and fire to high limit on demand through sr504 XX to TT interface.
    Hopefully this simplified it. If you have additional questions, Taco tech Support is a valuable resourse. 401-942-8000, ask for tech support. You can always reach out to me, the commercial guy!
    Thanks for your loyalty to Taco.
    Joe Mattiello
    N. E. Regional Manger, Commercial Products
    Taco Comfort Solutions
    Erin Holohan Haskell