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Wiring question, combining multiple zones in a 504EXP

Cliffy Member Posts: 24
Have a Taco SR504EXP zone relay and a Burnham ESC4 hot water boiler.

The house has two zones (two zones are unused in the 504), and I experimented combining the zones by jumping the thermostat cables within the Taco box and using one thermostat.  I found the boiler cycled less, and longer per cycle, with no adverse effect in the house. 

I'd like to try connecting the yellow wire, which is capped in the boiler junction box since the Taco box supersedes it's use, to the black wires powering the circulators coming out of the Taco box.  That would allow the circulators to run a bit when the heating cycle is terminated.  

Can I simply run the yellow wire to the Taco box and jump it to the black wire connections leading to the circulator?  Or disconnect the black wires going to the circulators in the Taco box and feed the yellow wire to the black wires going to the circulators?

There's no schematic for the Taco control, and I don't know if I'd be adversely back feeding power to the board.  Or if I'd blow something even trying this.

Is it worthwhile experimenting?  I could eliminate the 504, but aren't ready to go that far yet as the two unused zones in the Taco control will be used in the future.


  • Zman
    Zman Member Posts: 6,792

    It sounds like you are trying to connect the boiler circ and a zone circ to the boilers post purge relay?

    There is no reason to have both the taco and the boiler in control.

    You need to check the capacity of the boiler relay.

    It sounds like it will work, and be a good idea to switch control to the boiler.

    I would be more comfortable if you posted a picture or drawing of the piping.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Cliffy
    Cliffy Member Posts: 24
    edited January 2014
    Glad to

    Glad to post some pics. 

    Would ideally like to disconnect the two black wires from the board that supply power to the circulators and connect them with a single wire nut to the yellow wire that's in the boilers junction box.

    This is to tweak the remaining heat within the boiler before it cools down between cycles.  The yellow wire allows for "post purge" after a cycle completes whereby the circulators will run for a determined number of minutes.

    I just don't want to frazzle anything doing this, and since a schematic doesn't seem to be available for the board, am asking here for advice. 

    The first photo shows the lines leading to the circulators; the black wires are the ones I want to disconnect and tie to the yellow line from the boiler.  The second shows my jumpered thermostat connection which allowed us to turn off one thermostat and, as stated earlier, with a single zone it's running well.  The third photo is the control overall.


  • Cliffy
    Cliffy Member Posts: 24
    One more

    Here's the schematic on the back of the control cover.  It doesn't show the circuitry, but makes the connections clear - for whoever it might help.

    I also noticed this sheet has a 2005 date on it, and discovered looking at the photo of the board it's stamped 2007... it was three years old when installed!

  • Steamhead
    Steamhead Member Posts: 14,769
    I wouldn't do it that way

    those thermostat circuits are meant to remain separate. Crossing them like that may or may not shorten the unit's life, but why take chances?

    Also, trying to run two circs off a single lead won't work either. You want to control both the amount of heat generated AND where it goes. Whichever circ(s) you connect to the yellow lead will run whenever there is a call for heat to the boiler.

    The proper way would be to add outdoor reset, via the add-in card on the boiler. This would stop the burner when the water temp was high enough to heat the house at whatever the outdoor temp was at that moment, but keep the circs going as long as there was a call for heat.

    The only thing this setup won't do is circulator post-purge, i.e. allowing the circs to run for a few minutes after the boiler shuts off at the end of a running cycle. I'm experimenting with this on my system, and it does reduce the number of firing cycles especially in milder weather. I'm not aware of any multiple-relay units like your 504 that have this feature, if anyone knows of any please post the info here.
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Cliffy
    Cliffy Member Posts: 24
    What you're looking for is a

    Taco Post Purge Timer Power Port Plug-in Card  PC600-2 but from what I understand, and I could be mistaken, it controls only the first zone on the board.

    Perhaps you misunderstood my query.  I want to experiment doing away with the existing two zones and have one zone, also allowing us to utilize the post purge ability of the boiler.  Sometime in the future we'll be adding another zone or two, but for now just want to see how well the system works with one larger rather than two small zones.

    I'd expect the yellow and white wires from the boiler would be capable of powering more than two 007 circulators, are they not?
  • SWEI
    SWEI Member Posts: 7,356
    Single zone

    would remove the need for the SR504 completely.
  • Paul48
    Paul48 Member Posts: 4,470

    In the future, you know what to do. For the present, turn the control back over to the boiler.The manual gives a maximum amperage combined for boiler and circs.