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replacement for Electrozone relay

Soundart
Soundart Member Posts: 8
in Thermostats and Controls
Hello - I have a very old but working Hydrotherm gas/hot water boiler (HC 125). The relay is acting irregular and I am looking to replace it. The relay is electrozone RB-4A and is no longer available. I believe the output to the thermostat is 20 V. DC.

At this point, the boiler is 1 zone, 1 thermostat (the zone valves went bad a while back and I removed the internal switch cylinder). The house is fairly small and 1 zone heating works fine.

Can someone recommend a relay that would replace the Electrozone and provide 1 zone heating? The wiring on the current relay looks fairly straight forward.

Thanks!

Comments

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,269
    What controls the gas valve? Is it an end switch off of the Electrozone relay? If yes it is easy.

    If you are only using one thermostat, you just need to bypass the end switch and wire directly to the limit devices. basically connect the thermostat to the wires you remove from the end switch.

    Send a photo of the inside wiring connections of the Electrozone relay. Also send a photo for the boiler from far enough back to see that other controls. Then I can verify the vest step forward

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • Soundart
    Soundart Member Posts: 8




    I'll send a photo of the whole shebang later. Thanks.
  • Soundart
    Soundart Member Posts: 8


  • HVACNUT
    HVACNUT Member Posts: 6,282
    I don't know of any D.C. controlled switching relay that isn't a lot more than you need. Is there a Radio Shack around?
    I'm sure it would be easier to convert to 24 VAC controls. 
    Let's see the zone valve. I see a piece. 
  • pecmsg
    pecmsg Member Posts: 5,271
    HVACNUT said:
    Is there a Radio Shack around?

    Not for at least 10 years!
    PC7060
  • Soundart
    Soundart Member Posts: 8
    The zone valves are no longer functional and are permanently in the open position I am a novice and may be mistaken, but I think I need a relay that responds to the thermostat and will turn on the circulating motor and activate the burner until it reaches temperature. Since the zone valves are deactivated, is the 20 V DC output of any significance? Again, thanks for help!
  • HVACNUT
    HVACNUT Member Posts: 6,282
    If the zone valves are constantly open and the thermostats can handle AC switching, then a Taco SR501 or equivalent will work. TT on boiler is X1,X2.
    SteveSan
  • Soundart
    Soundart Member Posts: 8
    my current thermostat is Honeywell T822A. Will that be compatible?
  • HVACNUT
    HVACNUT Member Posts: 6,282
    Soundart said:
    my current thermostat is Honeywell T822A. Will that be compatible?
    Post a pic. I believe they are a mercury thermostat that mounts vertically in a Gem box. Should be ok.
  • MikeAmann
    MikeAmann Member Posts: 1,067
    Even if you did have to change the thermostat, they're cheap.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,269
    edited February 27
    The T822A thermostat is fine for the 24 VAC control.
    I placed the Electrozone numbers on the diagram in Blue

    Notice how terminal H and 3 on the Taco SR501 are equal to terminal 1 on the Electrozone. because there is a Jumper between H an 3 on the Taco

    This is the part you want to order
    https://www.supplyhouse.com/Taco-SR501-4-1-Zone-Switching-Relay

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    PC7060
  • Soundart
    Soundart Member Posts: 8
    Thanks so much to you all. I am hoping I can nurse the current relay until spring and then change over to the Taco. Seems very clear and not too difficult.
    EdTheHeaterMan
  • Soundart
    Soundart Member Posts: 8

    Thanks again to everyone who commented. Just replaced the electronzone with the Taco and it worked on the first try. Which, for me, is mind-blowing.

    John

    EdTheHeaterManMikeAmann
  • ratio
    ratio Member Posts: 3,777

    Looking at that control, it looks like a selenium rectifier on it (the green thing). That stuff is fairly not-very-good for you, & it should probably go to a hazardous waste drop-off point.

  • Dave Carpentier
    Dave Carpentier Member Posts: 620

    Never heard of it. Wiki says

    During catastrophic failure they produce significant quantities of malodorous and highly toxic hydrogen selenide.

    Smells that make you go hmmm

    30+ yrs in telecom outside plant.
    Currently in building maintenance.
  • Soundart
    Soundart Member Posts: 8

    I will do that. Thanks.

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