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Taco Zone Valve ZVC404-EXP pump wiring question

(there's a typo in the title I don't know how to correct.  It reads 404-EXP and should be 504-EXP)

Have a new system with a Taco 504-EXP with two zones connected.  Need to wire things in such a way that we can manually set the circulating pumps to be runnning continuously, regardless of the boilers function, to prevent baseboard heaters from freezing when it's sub-zero outside.

It appears I can take the hot wire from each zone at the board and run each to  independent three-way switches connected so either line current or current from the board will go to the associated pump. 

Will this damage or affect anything, and is there a better way of doing it?


  • lchmb
    lchmb Member Posts: 2,997

    Unless the zones are exposed to the outside you shouldnt have to worry about them freezing. If they are exposed, antifreeze the system and maintain it properly... You can purchase a pump to run, but once the zone valve close's there is no water moving through it...
  • 04090
    04090 Member Posts: 142

    Part of the joys of an 1800's house is unexpected frozen baseboard heaters.   We're well insulated, but with balloon framing that just seems to happen.

    The 504 switching relay control sends a signal to a circulator which apparently doubles as a zone valve.   My thought is to power the circulators continuously when it's below zero, and tapping the wire from the control will do that. 

    I don't know if the control watches amperage draw to be sure the circulator is on etc.  If it does, my idea is meaningless....

    But if it simply sends 120 volts and then tells the boiler to start up, I'm good to go that route - I think.
  • lchmb
    lchmb Member Posts: 2,997

    You had started with the 404 which is a zone control. Now mentioning the 504 changes things, yes it does work to control each zone. With that said, you could look into using constant circulation with outdoor and indoor sensors. That way your water flow is constant...and you'll run your system only to the temp needed to heat the house...
  • 04090
    04090 Member Posts: 142

    Like with a SR-501-2?  Would need an outdoor sensor and maybe some other things as well, and no idea how to combine the control wiring.  Tried googling some key words and that's all that came up.  What would you suggest using? 

    A simple walll switch worked for us many years with the old system, and we can continue to do that... just not sure if it's compatable with the new-fangled electronics.
  • Eric_32
    Eric_32 Member Posts: 267
    I am not a big fan

    of wiring it the way you are mentioning. The Taco box is designed to close the contacts and power the circ pump and burner when a zone calls for heat. The additional switch somewhere else has too much human error in it. You could set it up for constant circulation with a mixing  valve and outdoor sensor but...

     if power is lost for an extended time while freezing temps are outside, you are still up the creek with frozen heat lines.

    The simplest and best way to fix your issue in my opinion is to add glycol to the system, maintain it thru the years and don't worry about freezing pipes.


  • meplumber
    meplumber Member Posts: 678
    Concur with Eric.

    A properly maintained Glycol mix for the climate in your area. Assuming you are in Southern Maine per you nickname, a 30% mix is sufficient.

    I am in Downeast Maine and run a 30% mix in similar situations and have been doing it for years. This allows the system to run efficiently and normally with no special adaptations for freezing.

    As Eric mentioned, the glycol must be tested and maintained. At your annual service, your technician will take a small sample and test it for concentration and pH.

    Much better solution that your prior suggestion.
  • Ironman
    Ironman Member Posts: 7,225
    Pump Exercise Module

    I agree with Eric and MEP that glycol is the best approach, but Taco does have a card (PC610) that plugs into the expansion slot in the SR504 that will exercise the pumps to prevent freezing. It's timing is adjustable from a few seconds up to 30 days. But, as already stated, you'll have no protection during a power failure.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Pump Exercise Module

    My Ultra 3 U-control has both circulator exercising and freeze protect built in. The exercize part operates the selected circulators once every 48 hours of inactivity for 10 seconds. This may be useful for the heating circulators during the summer when they would otherwise never run.

    The freeze protect will fire the boiler at low fire and run the selected circulators if the heat exchanger gets below 40F and continue until it gets up to 45F. I have it run the boiler circulator and the radiant slab it this happens. I suspect that this is pretty much useless. It would matter only if the batteries went dead in the thermostats, or if someone turned them off.

    But where it  really matters is when the power is out, and then none of this does any good.
This discussion has been closed.