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Boiler voltage issue.

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Dviper12
Dviper12 Member Posts: 2
I'm working on a customers Weil Mclain boiler model CG-6-PIDN series 12 BTU 175,000 Honeywell thermostats #T87F. There are two zones for this split level home, they have two air handlers, one for the 1st floor and one for the 2nd floor which I have killed the power to at this point to isolate my issue. If you have one stat calling for heat and the other off I read 50 volts at the stats red and white wires, when you turn on the second stat so both zones are calling for heat you have 24 volts, this is the same if I take the reading at either stat. There are two zones each zone has its own Honeywell RA89A 1074 switching relay, I attached a diagram of the wiring that I traced out. I disconnected all the wires to verify voltage for both relays and the boiler transformer and each one is 24 volts on there own. I cant seem to figure out why I'm getting 50 volts in this situation and I don't understand why the system is wired the way it is with the two relays that have 24 volts transformers to energize the coil to pull in the relays that turn on the 120 volts to start the circulating pumps when they also are in the loop with the boilers 24 volt transformer. The R 24 volt red wire coming from the boilers transformer splits off and goes to the thermostats RH terminals, the G white wire coming from the boilers transformer splits up and goes to the two switching relays T terminals which also would have there own 24 volts and the W white wires from each thermostat goes back to the switching relays other T terminals which is the line side of the 24 volts. There are no zone valves in this set up just ball valves to isolate the zones for repairs. Can anyone help me on this to correct the issue the customer wants to have me install two Nest thermostats but I told him the 50 volt issue would need to be corrected first.

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  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,519
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    To my way of thinking it's all wrong. You have internal transformers in both the RA89As + the boiler transformer banging each other makes no sense.

    Yes you can phase the transformers and do some funky stuff but why complicate it?

    Each t stat should go to T & T on it's respective relay and that's it.

    First Zone Relay 1
    one stat wires to TT on the RA89A. The contacts on the RA89A go to the thermostat connections on the boiler control as shown on the boiler wiring diagram. The pump for this zone gets wired as shown on the boiler wiring diagram.

    Second zone Relay 2
    Wire the stat for the second zone to TT on this relay. This relay must have 2 sets of independent NO contacts.

    Wire 1set of contacts "in parallel" with the two wires from relay 1 above that go to the boiler control.

    The second set of contacts run the pump for zone 2. Find a hot wire to one side of the contacts. The other side goes to the pump

    or buy a zone panel
    SuperTechTinmanLouisFournier
  • SuperTech
    SuperTech Member Posts: 2,159
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    Sounds wrong to me. The best solution is to but a zone controller. This will also give you the ability to add a common wire to the thermostats, as long as it's not a Nest. They are a horrible choice for hydronic heating systems and you will probably get nuisance service calls related to them. Use them for target practice and sell your customer a Honeywell WiFi thermostat.
  • Jamie Hall
    Jamie Hall Member Posts: 23,282
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    The 50 volts you were reading is because -- as the above comments mentioned -- you have two transformers which, got wired in series -- and fortunately for you and the homeowner, in phase . Sheer luck. Fifty fifty chance. Out of phase and you'd have had zero volts -- and two burned out transformers.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    SuperTech
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
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    Wow! That's creative.

    Each thermostat to the TT on each 1074 no where else!

    Really the 1074's dont have an isolated end switch to send the call to the boiler so it isn't the right relay for a cold start boiler.

    As has been said get a switching really and be done with it. Then you'll even have a "C" terminal for the 3 wire wi-fi thermostats.

    Or you can do it the cheap way with a doorbell transformer and DPDT 24vac relays. I dont recommend this, its just what I do with all the stuff I have laying around :)
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • SuperTech
    SuperTech Member Posts: 2,159
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    > @Solid_Fuel_Man said:
    > Wow! That's creative.
    >
    > Each thermostat to the TT on each 1074 no where else!
    >
    > Really the 1074's dont have an isolated end switch to send the call to the boiler so it isn't the right relay for a cold start boiler.
    >
    > As has been said get a switching really and be done with it. Then you'll even have a "C" terminal for the 3 wire wi-fi thermostats.
    >
    > Or you can do it the cheap way with a doorbell transformer and DPDT 24vac relays. I dont recommend this, its just what I do with all the stuff I have laying around :)
    >

    What's the deal with those wire connectors? Did you run out of wire nuts?
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,519
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    My first post was wrong .You need a zone panel or two relays . Each relay must have 2 sets of isolated contacts. 1 set of contacts starts the boiler and the second set starts the respective pump. The contacts from each realy that starts the boiler are wired in parallel.

    @Jamie Hall your correct the transformers are somehow in series....50 volts
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,519
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    @SuperTech
    I haven't tried those yet supposed to be the new rage "wago" wire nuts or "lever" wire nuts I think they call them.

    I could see a use for them maybe in a box with the wires cut short.

    Don't know, they look too weird to use LOL
    SuperTech
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
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    Wago is who makes them. I use them almost exclusively for control work. I was resistant at first, but their ability with #14 stranded wire is far superior to wire nuts.

    Dont get me wrong I'm not going to wire a house with them, or any high current device. That box isn't my best work! It was for a friend in need, all stuff I had and much cheaper than an SR50x. Also notice it has a "C" wire for a wi-fi thermostat.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
    SuperTech
  • Dviper12
    Dviper12 Member Posts: 2
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    Thank you for all the feedback, I now understand what I need to do to correct this issue, This is a nice forum and I'm looking to be part of it from here on out. Once again thank you all for your take on this issue.
    Kind regards
    Dennis
    SuperTechCeacelSolid_Fuel_ManErin Holohan Haskell