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Taco power head terminal 3 as trigger.

grtpumpkin
grtpumpkin Member Posts: 12
Have had a nagging powerhead (555-050rp) failure on a zone valve that I'm using the #3 terminal as a trigger for a relay to turn on a fan for a heater once the end switch is engaged. This failure occurs every couple of years. Is it wrong to use the end switch as a turn on for a relay's coil? The relay's coil has a rating of 55 milliamps, which I considered a very miniscule draw to not hurt the powerhead's coil, but I could be wrong. The coil is definitely on it's way out as I can smell the electrical burn at the powerhead on a call for heat. The valve does turn on but immediately shuts off when the relay engages the fan. This has been working for a number of years this way but the powerheads keep failing every couple of years.
What's your thoughts?
Rich.

Comments

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,602
    edited January 2021
    How many transformers are involved? One for the thermostat and another for the fan relay? What is failing on the actuator, the end switch or the heater that expands the hydraulic piston?
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • Jamie Hall
    Jamie Hall Member Posts: 22,949
    Do I presume that you have a separate 24 VAC transformer and circuit wired through terminals 2 and 3 for that relay? That's what you should have...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    HomerJSmith
  • grtpumpkin
    grtpumpkin Member Posts: 12
    It's wired to a Taco ZVC405. Both transformers of the ZVC405 are wired in parallel.
    Rich.
  • grtpumpkin
    grtpumpkin Member Posts: 12
    edited January 2021
    The relay is wired to terminal 1 & 3 at the powerhead. This is where I feel the error may be. Was planning to try wiring the relay coil directly to the ZVC 405 at the same terminals. I think this way the relay's coil won't be pulling extra current through the powerhead's coil.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,602
    edited January 2021
    That is your problem. Can’t do that. Is the fan relay using one of the transformers from the ZVC?
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • grtpumpkin
    grtpumpkin Member Posts: 12
    No sir Mr. Young. The Fan relay is supplied with line voltage upstream from the ZVC 405, albeit on the same circuit.
  • grtpumpkin
    grtpumpkin Member Posts: 12
    Was also thinking activating the relay's coil with a temperature switch attached to the copper line and have it turn on once the valve is open and pipe gets hot.
    Any thoughts on that?
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,602

    No sir Mr. Young. The Fan relay is supplied with line voltage upstream from the ZVC 405, albeit on the same circuit.

    Ok. The relay has 120 volts going through the switches contacts. What is the relay coil using for power from #3 terminal of the zone valve? Not the 120V for the fan. That can’t happen.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,602

    Was also thinking activating the relay's coil with a temperature switch attached to the copper line and have it turn on once the valve is open and pipe gets hot.
    Any thoughts on that?


    That is the way I would do it
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • grtpumpkin
    grtpumpkin Member Posts: 12
    The relay coil pulls 55 milliamps. Thought it was low enough to trigger through the powerhead's coil. But apparently not.
    Rich.
  • mattmia2
    mattmia2 Member Posts: 9,469
    55 ma at 24v would be fine.
  • HomerJSmith
    HomerJSmith Member Posts: 2,408
    edited January 2021
    If you have two 24V transformer secondaries wired in parallel, they could be wired up out of polarity which could cause problems. There is a way to wire up two trans to work with each other.

    Jamie Hall's right.

    The thermostat transformer is in the ZVC 405 which is connected to the 1&2 screws of the ZV. One Fan relay coil lead should be connected to the #2 screw and the other lead of the coil connected to the 24V independent auxiliary trans and the other lead of the trans connected to the #3 screw. Walla, simple. The boiler control relay in the diagram is the Fan relay coil leads.


  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,602
    edited January 2021

    If you have two 24V transformer secondaries wired in parallel, they could be wired up out of polarity which could cause problems. There is a way to wire up two trans to work with each other.
    (Less diagram... See above post)

    This is automatically resolved when it is connected to a ZVC control. BUT adding a second function to the end switch, namely the Relay Coil Load for the fan relay is a problem not addressed by this diagram or the ZVC

    By looking at all the replies from @grtpumpkin i’m Wondering if there are 3 transformers are involved. He did not answer my query regarding the how the fan relay coil is powered satisfactory

    I want to know how the fan relay is powered by the #3 terminal. The entire circuit from power source to relay coil of the fan relay to the #3 terminal through the end switch to the common #2 terminal and the return trip back to the power source.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • HomerJSmith
    HomerJSmith Member Posts: 2,408
    edited January 2021
    Ed, he basically said that the Fan relay coil is wired between screw #1 and #3. That would probably activate the Fan relay, but it isn't the correct way to wire up a Fan relay coil to the ZV.

    My diagram is the correct way to wire it up. The #2 and #3 screws are the end switch connection that turns the boiler aquastat on, which turns on the the gas valve and boiler circulator. If you want the end switch function, you would use a 2 pole N/O relay with one pole turning on the 110V fan and the other pole turning on the aquastat 24V TT connections.

    By connecting the Fan relay coil to screw #1 and #3, you are commingling two circuits, I think.

    You know that the aquastat transformer is connected thru the aquastat relay to the #2 and #3 screws from the TT boiler connection. However....
  • HomerJSmith
    HomerJSmith Member Posts: 2,408
    If you are going to wire it up thru the ZVC 405, then it is a bit more complicated if it can be done. Is zone 5 being used? What zone is the Fan hooked up to?

  • Jamie Hall
    Jamie Hall Member Posts: 22,949
    Bottom line here, folks: the number 2 terminal is common. 1 is the power head. 3 is the end switch. A circuit must be 1 and 2, or 2 and 3. 1 and 3 is wrong, whatever the circuit might be.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • HomerJSmith
    HomerJSmith Member Posts: 2,408
    edited January 2021
    The ZVC 405 has two relays on that board. One, I think, is a 2 pole single throw relay in which one pole operated the TT aquastat contacts(24V) and the other pole operates the pump end switch XX contacts (120V). That relay can't be used in this application for the very reason that when any thermostat call for heat that relay will activate.

    The other relay is a single pole double throw relay ( Zone 5 Pump end switch, N/O-C-N/C) that is connected thru zone 5, the switched priority zone. That might work in this application if that zone is not connected to an indirect W/H. If it's available that relay maybe can turn on the Fan using the C-N/O connection(120V) in the no priority position when that thermostat calls for heat. Just a thought.

    Otherwise an independent transformer and relay must be used connected to the #2 and #3 connection on the ZV. This connection can be made to the #2 and #3 screws on the ZVC 405 for that thermostat and ZV. If the connection is done this way a single pole N/O relay would work because the ZVC 405 would control the TT to the aquastat eliminating one pole in the relay.

    Pics always helps especially in this regard. I don't know what boiler it is, I'm assuming it is a conventional boiler with an aquastat. I don't know where the Fan relay coil is connected to, the ZVC or the ZV.

    I failed my class in clairvoyance, so that's the limit in my predictive ability.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,602
    The original question is: why is the zone valve actuator failing every few years. 
    The answer is: the unconventional wiring of the fan relay

    The fix is to power the fan by way of an aquastat and let the end switch operate the burner and circulator as designed 
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • HomerJSmith
    HomerJSmith Member Posts: 2,408
    edited January 2021
    Good thinking Ed, yup, one could simplify by putting a Grundfos aquastat on the heat exchanger in the fan unit that just supplies 120V to the fan and forget all the wiring of the ZV and ZVC.

    The fan would just turn on when the HX reached 115 deg. Below are the type of thermodiscs that I had in mind.

    https://www.supplyhouse.com/Grundfos-595443-1-2-Clip-On-Aquastat-Kit-for-UP-Series-Circulators-5-8-OD-Piping-85F-105F

    https://www.supplyhouse.com/Grundfos-00595657-3-4-Clip-On-Aquastat-105F-115F