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Taco zone valves with minds of their own

jchandler22 Member Posts: 1
edited December 2017 in Thermostats and Controls
Hi All,

I have a forced hot water system with an oil furnace. 3 zones, each with a Taco zone valve and a Nest thermostat.

The odd behavior is that when a zone gets turned off, the valve closes, but then for a period of 1-2 minutes the dial on the zone valve cycles open and closed seemingly with a mind of its own. Sometimes halfway, sometimes all the way resulting in the furnace to kick back on for a fraction of a second. Once it finally decides to settle, it often stops halfway open/closed.

This only seems to happen when a zone is getting turned off, as opposed to when a zone is called on.

Anyone have an idea of what's causing this? Does it sound like an issue with the thermostat(s), the furnace, or the valves themselves?

Here's a video that shows what's going on (disregard the noises of baby & wife playing in the background).

Thanks for any thoughts.


  • NY_Rob
    NY_Rob Member Posts: 1,370
    Every time you see the green LED illuminate... power is being sent to the valve motor, that's why it's opening.

    What controls your zone valves- a zone controller or direct from t-stats?
    HVACNUT Member Posts: 5,890
    edited December 2017
    Do you have a common wire connected to C on the Nest?
    If not, it's considered a power stealing thermostat and will try to draw power though the ZV motors. If you have an extra wire to the thermostat, connect it to C, then take the same wire at the boiler and wire it to common on the transformer that operates the zone valves.
    When the valve closes, the lever will rest in the middle, but its closed.