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Switching Relay making error sound with blue light

Rep292
Rep292 Member Posts: 5
Hi all, I'd be grateful for any insight on an issue I'm experiencing with my hydronic heating system.
I have a Taco SR503 switching relay that enables my gas boiler to heat three zones (two radiator zonesand one in-slab hydronic zone.) Recently the relay started emitting this horrible sound (kind of like a grinding error noise) When I took the cover off, I noticed there is also a blue light that accompanies the sound coming from the Zone 1 box.

The whole system is heating fine, all zones are cozy and correspond with thermostat settings. The problem sound seems to come on in the evening, beep 3-6 times, sometimes it also hums in between beeping.

The boiler is a Burnham (US Boiler Company) model FCM070NH
Max Input: 70,000 BTU
Max Output, 63,000 BTU
Max Gas Supply Pressure 14.0 in w.c.
Gas valve outlet Pressure -0.015 in w.c.


Here is a video I took that documents the problem:

Please let me know if you have ideas!
I was not able to find a description of anything like this on this forum or elsewhere.
Thanks,
rep292

Comments

  • JUGHNE
    JUGHNE Member Posts: 8,924
    Relay chatter is the sound, are they plug in replaceable?
    Someone here will know if they are interchangeable within the control.

    But the blue light is electric arcing from the relay, not good.
    kcopp
  • Rep292
    Rep292 Member Posts: 5
    Thanks for the response! Yes, I think I just found the replacement relays on SupplyHouse for this model.
    https://www.supplyhouse.com/Taco-SR120-001RP-120-Volt-Replacement-Relay-11394000-p

    I also did some reading on "chatter" and it seems to be pretty common. Is the problem caused by a defective part? Or is there something wrong with my system that is causing the chatter and arcing?

    I am tempted to simply order the replacement relay, but would like to better understand the problem. Are there any good explanations or trouble shooting resources anyone can recommend?

    Thanks so much,
    rep292
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 10,213
    Could be a loose connection to the relay coil connections. Could be an overloaded relay.

    Replace it and see what happens and get a spare
    kcopp
  • Rep292
    Rep292 Member Posts: 5
    edited December 2020
    Upon closer inspection, it looks like all three relays are doing it at different times :( Could the problem be due to the fact that I have smart thermostats hooked up without the C-wire? I have read that this can cause electrical problems.

    In a different forum, one user says "with a volt meter in series you should be able to determine if stray voltage is coming back and causing a relay to buzz from a low voltage condition"

    (full discussion here: https://forum.heatinghelp.com/discussion/154520/nest-thermostats-taco-sr-504-switching-relay)

    I'm considering installing the diffusers (edit: I meant to write resistors) to see if that helps.
  • Jamie Hall
    Jamie Hall Member Posts: 17,009
    The most common problem -- by far -- causing a relay to chatter when energized, or for contact bounce when energizing -- is inadequate voltage. This is particularly true if the relay is relatively "young" in terms of cycles, and is even more true if the chatter is particularly bad as it is pulling in.

    Relays -- and solenoids in other applications, which are similar -- are designed to pull in at a particular current, or -- within reason -- more. They need more current during the pull in sequence than they do once closed. The current through a relay is a function, in turn, of the voltage applied to the coil and the impedance of the coil, which is almost (but not quite) constant -- so it is voltage we must look at.

    Therefore... if there is any other resistance in the circuit powering the relay -- bad wire connections, a current draw in series (such as a current stealing thermostat!!! -- more on that later) you can have problems with chatter or delayed or erratic operation, all of which can damage the load contacts.

    Now the opposite problem occurs with a situation where some current is allowed to pass through the relay coil even when the controlling circuit contacts are open. Once a relay is pulled in, the current it takes to keep it that way is much less, depending on the relay design. If there is a situation where a current is permitted to flow across the coil, or where there is a current draw with the controlling contacts open, the relay may appear stuck at times, or chatter as it is opening. This is the case with current stealing thermostats: in them the circuit is not opened completely when the thermostat contacts or circuit open; rather a small current is allowed to continue to charge the battery or capacitor in the thermostat. Depending on the specific combination of relay coil and relay adjustment and the effective resistance of the charging device, this can -- and does -- cause erratic operation of the relay on opening.

    Frankly, from the electronics standpoint, using a two wire power stealing arrangement is an exceedingly poor and trouble prone design and should never be used.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Rep292
  • ratio
    ratio Member Posts: 2,918
    A relay chattering like that is unlikely to be a relay failure (although operation like that will shortly result in failure). Look for abnormally low voltage, paying particular attention to connections.
  • Rep292
    Rep292 Member Posts: 5
    edited December 2020
    OK, so it sounds like I should run C-wire to my thermostats. I wish my electrician had thought to do so! :'(

    Should I try adding the resistors first or is that not applicable to my problem?

    Thanks everyone for your expert advice.
  • Jamie Hall
    Jamie Hall Member Posts: 17,009
    The resistors will make the problem worse, not better.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • JUGHNE
    JUGHNE Member Posts: 8,924
    If you are able, remove the Nest and jumper the 2 wires at the wall. If that zone still chatters then you have some other problem.
  • SteveSan
    SteveSan Member Posts: 101
    How many Nest t-stats do you currently have? The sr503 only has a 15va transformer so if you have more than two Nest you would need to wire in an external transformer. Make sure the Nest have been pre-charged and please call into Taco Tech Support anytime between 8am-5pm EST Mon-Fri.
  • Rep292
    Rep292 Member Posts: 5
    Thanks, everyone, for helping me clarify that the problem is not with my Taco relays, but rather with the incompatable thermostats that were installed. Since I am just a humble homeowner and have no experience snaking wire, I've decided to simply replace the smart thermostats with programmable ones.

    Here's what I decided to get after several hours of research: https://www.supplyhouse.com/sh/control/product/~product_id=TH140-28-01-B
    It was really hard to find a heat-only programmable model!

    This experience has also shown me that I need to find a more knowledgable contractor for servicing my hydronic heating system. I checked out the Find-a-Contractor feature of this site but nothing came up for the mid-Hudson Valley. Anyone out there work or know someone who works in the area of Kingston, NY?