Zone Valve/Relay Wiring Help Needed

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by mattm, Jan 15, 2007.

  1. mattm

    mattm New Member

    Messages:
    3
    Hello-

    I am in need of some wiring advice. My heating system is a hybrid system - gas fired boiler. I have 5 zones of under-floor radiant heat (PEX), and 2 zones of conventional hot water baseboard. The baseboard zone valves are 24V Taco 571 valves, three wire, and the under-floor radiant are 4 wire (with end switch) 24V valves. There are two circulator pumps, one for the baseboard and another for the under-floor radiant. There are also two pump control relay boxes, one for each system. The boiler control is a Honeywell Aquastat Relay L8148E.

    My problem is that when the under-floor radiant zone calls for heat, it's own pump kicks on as it should, but I also need to tell the boiler to turn it's circulator pump on and fire to heat the water. As of now, I have the end switches from the under-floor radiant wired to the "thermostat" terminals on the boiler relay control box. This works fine and operates the boiler when a under-floor zone calls for heat. The problem is that when a baseboard zone calls for heat, it now also turns the circulator on for the under-floor radiant, whether it calls for heat or not.

    Do I need some kind of additional relay or do I have the wiring wrong?

    Any help would be appreciated.

    Thanks,

    Matt
    NJ
  2. Rancher

    Rancher Guest

    Can you give us a wiring diagram of what you have?

    Rancher
  3. mattm

    mattm New Member

    Messages:
    3
    Hi-

    Thanks for the reply. Here's some more info.

    Photos and schematics can be found at:

    http://www.mattmccool.com/heat

    My original system was a 4-zone hot water baseboard system. I am in the middle of a major remodel on half the house (which contained 2 of the 4 zones). Since that part of the house was gutted, I decided to run a PEX system under the floors, and while I was at it - I put separate loops under those 5 rooms for maximum temperature control, hence the 5 radiant zones.

    The original 4 zone baseboard system had one large circulator pump, 4 zone valves (obviously) all controlled by the Honeywell Aquastat L8148E.

    So...I removed the baseboard in that part of the house and the two respective zone valves - only. I ran the PEX and installed a manifold with mixing valve, etc. The control box is simple, just a large 24V transformer and a relay to turn on the circulator pump. There are 5 separate zone valves, with end switches that control the PEX zones.

    My problem is that when any of the 5 PEX radiant zones call for heat, I need the boiler to fire and the original circulator pump to go on, as no water seems to flow through the boiler if that pump is not running. All the end switches are wired together (for the PEX zones) and I have them wired to terminals TV and T on the L8148E (see photo). (This is also where the ES wires for the baseboard Taco 571 valves are wired). When a PEX zone calls for heat - everything works great - both circulator pumps trigger, the auto-damper opens and the boiler fires. BUT when NO PEX zone calls for heat but a baseboard zone calls for heat, not only does the original baseboard circulator pump run, but the PEX pump runs too. That's what I am trying to avoid - I don't want the PEX pump to run if it does not have to.

    Photos and schematics can be found at:

    http://www.mattmccool.com/heat

    Hope this helps!


    Thanks again,


    Matt
  4. Rancher

    Rancher Guest

    Sounds like you have the pumps, or the relay/control for the pumps on both the pex system and the boiler system wired in parallel, you need to use another relay to isolate the pex pump from the boiler pump, i.e. have the same signal that the pex system uses to tell the boiler pump to come on to trigger the relay to tell the pex pump to come on. Then when the old boiler system tells it's pump to come on the pex pump will be isolated.

    Rancher
  5. mattm

    mattm New Member

    Messages:
    3
    Another relay makes sense - is there one you might recommend? How would this new relay be wired?

    Thanks for the help,

    Matt
  6. Rancher

    Rancher Guest

    What turns on your relay for the pex pump?

    What's an end switch, I'm not a hydronic HVAC guy and this is new term to me.

    I'm thinking on your Aquastat control that the TV and T terminal want to see just a contact closure?

    On that on-line auction place there are always cheap normally new relays for sale.

    Rancher
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