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Troubleshooting hot water switching relay

Paul_85 Member Posts: 3
Trying to troubleshoot a "no hot water" problem. I think I have it mostly understood, just trying to figure out next steps. Hot water is fed from an indirect water heater connected to the priority zone of an oil boiler, using an Argo ARM-4P zone relay. Here's where I'm at so far:
  • The hot water heater was calling for heat and firing the boiler (xx and ZC/ZR relays were lit), and boiler was firing.
  • No power was being provided to the zone circulator - no light on the relay, and no voltage measured at the circulator.
  • The circulator is fine - I switched the wiring to feed the circulator off of the ZC/ZR relay power and everything works as expected - circulator runs, hot water is back.
  • It's not a persistent problem. Sometimes the zone lights up, and sometimes it doesn't.
  • The relays themselves are fine, or at least appear fine. While the hot water heater was calling for heat and the relay light was on, I switched in all of the relays to the hot water heater zone. All of them lit up.
My assumption from all this is that it's likely some loose connection or intermittent failure in the zone relay itself. So, my questions - (1) is that a reasonable assumption / is there anything I'm missing? (2) if that's right, is there anything I can / should do about it, or is this a replace the whole relay controller type of thing?

I have time to figure it out - the only zone that will call for heat for the next couple of months will be the hot water heater, so keeping it on the ZC/ZR seems like it'll work for now.


  • Jamie Hall
    Jamie Hall Member Posts: 23,280
    The most likely culprit is a loose connection … somewhere. If it's plugs, try unplugging and looking at all the pins and sockets and check for corrosion or overheating, then plug it back in. Otherwise -- make sure all connections are clean and tight. Make sure all wires are looking good.

    If that doesn't work, are the relays plug in? If so, try swapping them.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    edited May 2020
    If you jump T-T on the priority zone and are not getting 120v out of Zone 1 L & N, the relay is bad. You can order a replacement or switch it out from an unused zone.
    If it does check out, then it’s the wiring.
  • Paul_85
    Paul_85 Member Posts: 3
    Thanks very much to both of you, seems like something must be intermittently loose somewhere - the relays all work when I switch them into other zones and force them to call for heat. Appreciate the help...
  • Alan (California Radiant) Forbes
    As a last resort, measure voltage at the "L" and "N" terminals for the indirect pump at the Argo control. If you have no power there, replace the control.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,833
    edited June 2020
    This can be a pain in the A$$. Sometimes I remove the actual printed circuit board from the control case. Be careful if the control uses plastic standoffs, they can break and you will have a problem with reassembly. Observe the back of the PC board, look for burnt spots or areas where the solder may have been poorly applied. Over time the poor connection can overheat and melt the solder away from that connection. If you can carefully solder the bad spot, you can continue to use the repaired control.

    This can be fixed with a small soldering iron and a drop of solder.

    Trash this one

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics