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Heating issues (thermostat and zone valve changed)

A two zone (2 zone valve - Honeywell with a Taco SR501 switching relay and a single circulation pump) Hydrotherm HC-125C hot water boiler.
Recently, I am having intermittent heating results.
When the thermostat calls for heat, i see the lights on Taco unit - Power (red) and Zone 1 (green), and the boiler fires up and all is good. But often times I hear a buzzing sound after all the lights on Taco are lit and no heat is generated. I have changed the thermostat and zone valve. It worked in the beginning, but later on we are again at the same position, intermittent heating.
The second zone works fine.
Has anyone dealt with this before? Any solutions?



  • Jamie Hall
    Jamie Hall Member Posts: 22,934
    Check all your connections. You may be pushing the limit on your transformer, and any resistance in the circuit may be giving you a low voltage problem, and the relay(s) will buzz but not pull in.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EBEBRATT-Ed Member Posts: 15,335
    Buzzing is usually a relay that has dirt on the coil armature if it has any open type relays. Or you could have a loose connection somewhere.