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Boiler not firing/extremely delayed when hot water calls for heat.

jcarley
jcarley Member Posts: 4
in Domestic Hot Water

First time posting, thanks in advance for any and all help in this matter and the help and information I've already received from reading the forums.

Moved into a new house in Maine about a month ago, was still cold out and was running hydronic heat. Now that it's warming up I've noticed my hot water will not last for more than one or two showers. I'm certainly not expert in this matter but feel like I'm genuinely stumped and not just completely clueless.

I'll start with equipment;

Biasi SG3 boiler , riello 40 burner on natural gas, weil-mclain gp30 indirect water heater, taco zvc 404.

I have 3 zones; lower level, upper level and hot water heater. When either thermostat for heat is turned on the system seems to work perfectly. When domestic hot water is depleted, it will call for heat, valve will open, but boiler will not fire (it does seem that if you wait overnight the water will be hot again). Experimenting with system, I swapped wires for tank to a different zone, same behavior. If I turn thermostat on upper or lower level on, I will get hot water as the valve is open which is why I didn't notice this when it was colder and was running heat.

It would seem as though boiler, controller, circulator, and thermostat is all working correctly....except it isn't.

Any help or advice on direction of next diag step is greatly appreciated.

Comments

  • mattmia2
    mattmia2 Member Posts: 12,848

    Can you take a picture of the zone valve for the indirect and the wires connected to it? I suspect that it is wired so that the end switch in the zone valve calls for the boiler to fire and the end switch is bad(or the valve is sticking and not opening all the way) but the boiler could be controlled by the zone control instead. A picture of how the zone control is wired would be good too.

  • jcarley
    jcarley Member Posts: 4
    https://forum.heatinghelp.com/discussion/comment/1854922#Comment_1854922

    Thanks for your reply. I've attached photos that hopefully will help. The valve is wired the same as the two others that work without issue and it appears that they are all wired to one end switch. When the zone calls for heat, the valve does open and I've been experimenting and if I turn on the thermostat for another zone the boiler will fire and the domestic hot will heat up and it also seems like when I shut off the thermostat for another zone that the boiler will continue to heat the domestic hot until it reaches temp.

    The last two photos are the thermostat and valve LEDs lit up and valve in open position but boiler not firing and water not circulating.

    IMG_20250507_190424709.jpg IMG_20250507_190214805_HDR.jpg IMG_20250507_190156554.jpg 17466594395388414739070805271017.jpg 17466595092244853118351504707424.jpg 17466595514631211310833410706875.jpg
  • mattmia2
    mattmia2 Member Posts: 12,848

    Trace where the end switch wires from the zone valves and from the zone control go.

    My bet is if you jumper the end switch terminals on the indirect zone while there is a call for the indirect the boiler will start. It won't hurt anything because they should be shorted when the valve is open anyhow.

    jcarley
  • mattmia2
    mattmia2 Member Posts: 12,848

    The end switch wires from the zone valve go in to the zone control terminals 3 and 4? if that is the case the end switch in the zone valve is almost certainly bad.

    jcarleyjringel
  • jcarley
    jcarley Member Posts: 4
    https://forum.heatinghelp.com/discussion/comment/1854928#Comment_1854928

    Well my friend I owe you a debt of gratitude and I still don't know the issue but you've given me direction. The end switch is wired directly to a Honeywell L7224U aquastat/controller. I don't understand why two zones were working but this one was not but sure enough I jumped the two terminals and the boiler fired immediately. All the wires in the Honeywell controller appear to be installed correctly and lugs are tight but there does appear to have been some overheating of wiring inside the controller.

  • mattmia2
    mattmia2 Member Posts: 12,848

    swap one of the working and non working zone valve powerheads and see if it follows the powerhead.

    i'm pretty sure the end switch terminals from the zone valve land on terminals 3 and 4 of the zone valve controller and the zvc passes that signal to the end switch connection to the boiler.

    EdTheHeaterMan
  • jcarley
    jcarley Member Posts: 4
    https://forum.heatinghelp.com/discussion/comment/1854934#Comment_1854934

    Bingo! Swapped powerheads and behavior followed powerhead. I owe you lunch sir!

    HeatingHelp.commattmia2

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