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I have two zones in my house, upstairs & downstairs. Baseboard heat/ boiler/ propane. I noticed that regardless of the thermostat reading (nonprogrammable circle honeywell heat only) i can feel significant heat coming off the baseboard heaters. I have the thermostat set as low as 50, but still it gets up to 70 degrees up there. I can hear an audible "click" if I dial the thermostat above the current temperature, but I'm wondering if the thermostat is the issue.

I've inspected the zone valve on the boiler to see if it was manually set to "open", but its still set to auto for both zones.

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  • If you set the upstairs valve to "close" does it actually shut off flow to the upstairs? It's possible that the valve is stuck. It's also possible that the valve works to stop water flow, but that the "auto" setting no longer works to close the valve on demand. Have you confirmed that the wiring from the upstairs thermostat to the valve is good and all connections are still secure?
    – FreeMan
    Jan 28, 2022 at 13:25
  • I haven't checked the wiring yet. I'm guessing I could check continuity with a multimeter? I just figured the wiring was ok from hearing the thermostat click. The honeywell zone valve only has an auto or manual open setting, so no luck manually closing Jan 28, 2022 at 13:56
  • I'm no expert on water based heating, those were just the obvious things I thought of. A continuity test does seem like a reasonable thing to do to be sure the wiring is up to snuff. A simple tightness test to ensure the wires are still screwed down firmly to their contacts might be a simple first step.
    – FreeMan
    Jan 28, 2022 at 14:00
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    Try manually setting the valve to the open position. That's how I noticed mine was stuck just the other day - it was very hard to move to open manually. If it's stuck in full open, you would then also notice that it sounds different when the lever returns to closed, as compared to your other zone valve. In my case, it was the electric valve actuator that had seized, the actual fluid valve part was still operational, so it was a quick and easy fix. Jan 28, 2022 at 14:41

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You probably have thermo-siphoning causing heat delivery without the pump running. Warm water rises into the loop and cold water falls from it, causing unintended heat delivery. If the pump is not running when the the thermostat is off, that's probably it.

There are various approaches to stop that - "heat trap" pipe loops and check valves that permit pumped flow but prevent thermo-siphoning are the most common.

If the pump is running when the thermostat is off, that's a different problem.

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